Patent Publication Number: US-8976979-B2

Title: Audio signal dynamic equalization processing control

Description:
RELATED APPLICATIONS 
     The present application is a continuation filed under 35 U.S.C. 111(a) of International Patent Application No. PCT/US2010/034559 having International Filing Date 12 May 2010 titled AUDIO SIGNAL DYNAMIC EQUALIZATION PROCESSING CONTROL, the contents of which are incorporated herein by reference. International Patent Application No. PCT/US2010/034559 claims priority of U.S. Provisional Patent Application No. 61/181,206 filed 26 May 2009 and titled AUDIO SIGNAL DYNAMIC EQUALIZATION PROCESSING CONTROL, the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates generally to signal processing of media data, such as signal processing of signal data for quality enhancement. 
     BACKGROUND 
     Equalization processing of an audio signal is commonly used to alter the frequency response of an audio signal to be within a user specified range and is typically achieved by using an equalization filter whose frequency response can be adjusted by a user for one or more reasons, such as the resulting audio signal having improved fidelity, emphasizes certain frequencies or ranges of frequencies, has undesired frequency components such as noise removed, and/or matches perceived timbre of multiple audio signal pieces, such as songs on a CD or multiple compressed MP3 audio signal files. Audio signal equalization is also commonly used in film and television production to improve the quality of the sound, modify and/or match the timbre of audio signal in different scenes or to match individual audio signal streams which comprise a film or television soundtrack. Audio signal equalization can also be used to modify specific frequencies and to make audio signal perceptually louder, as well as to compensate for frequency dependent deficiencies in an audio signal reproduction system. 
     Many types of equalizations are known. Such equalizations, however, do not take into account the time varying nature of the audio signal itself. 
     Recently, perceptual domain processing has been invented that takes into account the variation in the perception of audio depending on the reproduction level of the audio signal. See, for example, International Application PCT/US2004/016964, published as WO 2004111994. Such processing includes determining and adjusting the perceived loudness of an audio signal in an improved manner. A psychoacoustic model is used to calculate a measure of the loudness of an audio signal in perceptual units. Such perceptual domain loudness measure is referred to as specific loudness, and is a measure of perceptual loudness as a function of frequency and time. When applied to equalization, true dynamic equalization is carried out in a perceptual domain to transform the time-varying perceived spectrum of the audio signal to be closer to a desired time-invariant perceived spectrum. This form of equalization matches a desired target perceived spectrum while preserving the perceived dynamic range. This takes into account the dynamic range and perceived loudness of the audio signal. 
     While it is known how to achieve such perceptual domain dynamic equalization processing, it would be advantageous to provide mechanisms for controlling one or more properties of the equalization. Example of such control include in the case of a single preset target perceived spectrum, how much equalization to achieve. In the case of more than one preset target perceived spectra, controlling how much the ultimate target perceived spectrum includes each of the preset spectra. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a set of filters spaced uniformly on the Equivalent Rectangular Bandwidth (ERB) scale and used to determine frequency bands for perceptual domain processing according to embodiments of the present invention. 
         FIG. 2A  shows a simplified block diagram of a feed-forward embodiment of perceptual domain dynamic equalization signal processing apparatus in which pre-processing separates an input audio signal into frequency bands. 
         FIG. 2B  shows a simplified block diagram of a feed-forward embodiment of a dynamic equalization signal processing apparatus. 
         FIG. 3  shows a simplified block diagram of an apparatus embodiment for processing audio by perceptual domain or not necessarily perceptual domain dynamic equalization as specified in accordance to one or more features of the present invention. 
         FIG. 4A  shows a basic slider control interface for dynamic equalization on a media device according to some embodiments of the present invention. 
         FIG. 4B  shows a basic knob control interface for dynamic equalization on a media device according to some embodiments of the present invention. 
         FIG. 5A  shows a basic slider control interface for dynamic equalization on a media device for application of two dynamic equalization preset spectral profiles according to some embodiments of the present invention. 
         FIG. 5B  shows a basic knob control interface for dynamic equalization on a media device for application of two dynamic equalization preset spectral profiles according to some embodiments of the present invention. 
         FIGS. 6A and 6B  show a slider control interface and a knob control interface, respectively, each providing a user control of the application of three different dynamic equalization preset spectral profiles on a media device according to some embodiments of the present invention. 
         FIG. 7  shows a control interface with a two dimensional user control element of a control interface for control of the application of four dynamic equalization preset spectral profiles according to some embodiments of the present invention. 
         FIG. 8  shows the two-dimensional control element of  FIG. 7  with overlaid coordinate axes that are used to translate the user input position to parameters that are used to compute the equalization spectral profile for dynamic equalization according to some embodiments of the present invention. 
         FIG. 9  shows a two-dimensional control element of a control interface for user control of the application of nine dynamic equalization preset spectral profiles according to some embodiments of the present invention. 
         FIG. 10A  shows an example control interface with an input control mechanism that includes a rotary bass control and a rotary treble control according to some embodiments of the present invention.  FIG. 10B  shows the overall desired spectral shape for dynamic equalization using the control of  FIG. 10A , and  FIG. 10C  shows how the frequency ranges that the bass and treble input control mechanisms vary in this example. 
         FIG. 11A  show an example control interface with an input control mechanism that includes slider controls for multiple frequency bands analogous to a multi-band equalizer according to some embodiments of the present invention.  FIG. 11B  shows the overall desired spectral shape for dynamic equalization using multiple input controls of  FIG. 11A , and  FIG. 11C  shows how the overall frequency range is divided into ranges that the respective slider controls of  FIG. 11A  vary in this example. 
         FIGS. 12A and 12B  show two alternate embodiments of a control interface for integrated dynamic equalization control including selecting a dynamic equalization preset profile and varying the amount of dynamic equalization applied, according to some embodiments of the present invention. 
         FIG. 13  shows a simplified flow chart of an embodiment of controlling an audio signal processing apparatus using control interface for integrated dynamic equalization control such as shown in  FIG. 12A  or  12 B to vary the amount of dynamic equalization to apply, to select one of a set of pre-defined dynamic equalization preset spectral profiles, and to define and save a dynamic equalization preset spectral profile, in accordance to some embodiments of the present invention. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Overview 
     Described herein are apparatuses for and methods of carrying out dynamic equalization processing of an audio signal, such as perceptual domain dynamic equalization and other types of dynamic equalization, and apparatuses for and methods of controlling such equalization processing of the audio signal to dynamically adjust the time-varying spectrum of an audio signal to more closely match a user specified target time-invariant audio signal spectrum. Also described herein are computer readable media that include instructions that when executed by one or more processors of an audio signal processing apparatus carry out the methods. 
     Also presented herein are improved approaches for users of media devices—in general, audio signal processing apparatuses—to create, modify and apply the target time-invariant audio signal spectra used in dynamic equalization processing. 
     One embodiment includes a method of operating an audio signal processing apparatus to process an audio signal. The method includes accepting from a control interface a user-defined dynamic equalization (DEQ) spectral profile based on a blending of one or more selected DEQ preset spectral profiles. The blending is based on a set of one or more blending parameters. The control interface provides a mechanism for a user to set the one or more blending parameters. The blending parameter for the case of a single DEQ preset spectral profile is a parameter indicative of the amount of DEQ to apply according to the single DEQ preset spectral profile. The method further includes processing an audio signal according to the user-defined PDEQ spectral profile to generate a processed audio signal. The processing including determining a spectral measure that is modified to dynamically adjust the time-varying spectrum of the audio signal to match a time invariant spectral profile according to the user-defined DEQ spectral profile. In the case of perceptual domain dynamic equalization (PDEQ), the processing including determining a perceptual domain spectral measure that is modified to dynamically adjust the time-varying perceived spectrum of the audio signal to match the time invariant spectral profile according to the user-defined DEQ spectral profile. 
     In some embodiments of the method, the control interface including one or more control elements configured to accept a user input, and the method includes presenting the control interface to the user so that the user can apply an input mechanism to control the control element(s). 
     In some embodiments of the method, the control interface further includes at least one control element for selecting the one or more DEQ preset spectral profiles from a set of DEQ preset spectral profiles. 
     Different embodiments include different types of control elements, such as virtual or actual slider control elements, and/or virtual or actual rotary control elements. Some embodiments include a two-dimensional control element configured to accept a user indication of a location on an area defining the two-dimensional control element. 
     One embodiment includes a computer-readable medium configured with instructions that when executed by one or more processors of a media processing apparatus cause carrying out a method. The method is as described in the above four paragraphs. 
     One embodiment includes a media processing apparatus that includes one or more processors configured to determine a user-defined dynamic equalization (DEQ) spectral profile by blending one or more selected DEQ preset spectral profiles based on a set of one or more blending parameters. In the case of a single selected DEQ preset spectral profile, there is a single blending parameter indicative of the amount of DEQ to apply according to the single DEQ preset spectral profile. The one or more processors are further configured to process an audio signal according to the user-defined DEQ spectral profile to generate a processed audio signal, the processing including determining a spectral measure that is modified to dynamically adjust the time-varying spectrum of the audio signal to match a time invariant spectral profile according to the user-defined DEQ spectral profile. In the case of perceptual domain dynamic equalization (PDEQ), the processing including determining a perceptual domain spectral measure that is modified to dynamically adjust the time-varying perceived spectrum of the audio signal to match the time invariant spectral profile according to the user-defined DEQ spectral profile. The media processing apparatus further includes a storage subsystem, and a control interface including one or more control elements configured to accept a user input including values for at least some of the set of one or more blending parameters for defining the user-defined DEQ spectral profile. In some versions, the storage subsystem is configured with instructions that when executed by one or more of the processors, cause the determining of the user-defined DEQ spectral profile and the process of the audio signal. 
     Particular embodiments may provide all, some, or none of these aspects, features, or advantages. Particular embodiments may provide one or more other aspects, features, or advantages, one or more of which may be readily apparent to a person skilled in the art from the figures, descriptions, and claims herein. 
     Background Art: Traditional Equalization 
     Many kinds of traditional equalization filters are known, and each has a different behavior in regards to the frequencies that they attenuate or boost. With traditional equalization, filtering is applied to an audio signal in order to change its spectrum. A peak equalizer raises or lowers a range of frequencies around a central point in a bell shape. A peaking equalizer with controls to adjust the level (gain), bandwidth (denoted by Q) and center frequency is called a parametric equalizer, with the parameters the gain, bandwidth, and center frequency. A similar peaking equalizer but with no control of the bandwidth, e.g., a bandwidth fixed by the filter designer, is sometimes called a quasi-parametric equalizer or a semi-parametric equalizer. 
     A pass filter equalizer attenuates either high or low frequencies while allowing other frequencies to pass unfiltered. Such filters include a low pass filter, a high pass filter, and a band pass filter, which combines the properties of a high pass and low pass filter. 
     Shelving-type equalizers increase or attenuate the level of a wide range of frequencies by a fixed amount. A low shelf will affect low frequencies up to a certain point and then above that point will have little effect. A high shelf affects the level of high frequencies, while below a certain point, the low frequencies are unaffected. 
     In many equalization hardware and software implementations, it is not uncommon for all three types of equalizer filters, peak, pass and shelving to be part of the signal processing path to modify an audio signal. 
     Another common type of equalizer is a graphic equalizer, which includes controllers such as a bank of sliders or other controllers for boosting and cutting different bands (frequency ranges) of an audio signal. Normally, these bands are tight enough to give at least 3 dB or 6 dB maximum effect for neighboring bands, and cover the range from around 20 Hz to 20 kHz. 
     An example of a simple graphic equalizer is a 4-band equalizer that might have bands at 20 Hz, 200 Hz, 2 kHz and 20 kHz. A typical graphic equalizer for live sound reinforcement might have as many as 24 or 31 bands. 
     Spectral matching equalization is known in which it is desired to match the frequency response of a target audio signal to that of a reference audio signal. An audio engineer listens to the reference audio and manually creates an equalization setting that will make the target sound like the reference. Such manual spectral matching equalization can be very time consuming and often still yield unsatisfactory results, e.g., because of the time varying nature of the target. 
     In recent years several automatic spectral matching equalization methods have become available. These methods are often provided in the form of a software plug-in for a digital audio signal workstation. Examples of commercially available solutions include Match EQ™, part of the LogicPro7™ Plug-in by Apple Computer, Inc., of Cupertino, Calif., Freefilter by Steinberg Media Technologies GmbH, of Hamburg, Germany, and CurveEQ™ by Aleksey Vaneev (“Voxengo”) of Syktyvkar, Komi Republic, Russia. Such methods typically operate as follows: first a reference audio signal is analyzed to generate an averaged static reference spectrum. A target audio signal is also analyzed to generate a second averaged static reference spectrum. The two spectra are compared to create static equalizer that attempts to match the spectral characteristics of the target audio signal to those of the reference audio signal. Because the resulting equalizer does not take into account the time varying spectrum of the target audio signal, the results are often unsatisfactory. Automatic spectral matching equalization is also highly dependent on the user selected audio signal for the first two analysis steps, particularly the analysis of the target audio signal. 
     Recently there have been attempts to carry out equalization that combined dynamic range compression with multi-band equalization. Examples include Dynamic EQ™ by T.C. Electronic A/S of Risskov, Denmark, and Multi-Band Dynamics™, part of the XFX2™ suite of plug-ins by Sony Creative Software Inc., of Madison, Wis. Four definable bands can be configured to work in either static or dynamic modes, or a mixture of both. Each band can be configured as a parametric equalizer or as a high or low shelving filter. Each band also includes compression, using compression parameters such as threshold, attack time, release time and gain. The compression does take into account the underlying time-varying nature of the audio signal being processed, but does so in a rather coarse manner. 
     Perceptual Domain Dynamic Equalization (PDEQ) 
     A more satisfying true dynamic equalization method is carried out in a perceptual domain to transform the perceived spectrum of the audio signal from a time-varying perceived spectrum to be closer to a substantially time-invariant perceived spectrum. This form of equalization matches a desired target perceived spectrum while preserving the perceived dynamic range. This takes into account the dynamic range and perceived loudness of the audio signal. The process is called Perceptual Domain Dynamic EQ or PDEQ herein, and refers to an audio signal equalization method that includes intentional transformation of an audio signal&#39;s time-varying spectrum to match more closely a target time-invariant spectrum while still preserving the original dynamic range of the audio signal. 
     With traditional static equalization, a simple fixed filtering is applied to the audio signal in order to change its spectrum. For example, one might apply a fixed bass or treble boost with simple shelving EQs. However, such processing does not take into account the spectrum of the audio signal being processed and may therefore be inappropriate for some signals. As one example, audio signals that already contain a relatively large amount of bass or treble may become unacceptable to a listener following additional frequency boosting. With PDEQ, the time-varying spectrum of the signal is measured and the signal is then dynamically modified in order to transform the measured spectrum to more closely match a desired static shape. If the spectrum of the audio signal is already close to that of the desired shape, then little modification is made to the audio signal. If the spectrum is significantly different from the desired shape, then the resulting modifications may be large. These modifications adapt over time as the spectrum of the processed audio signal changes relative to the spectrum of the desired shape. 
     Seefeldt recently described PDEQ in International Patent Application No. PCT/US2005/038579 published as WO 2006047600 titled CALCULATING AND ADJUSTING THE PERCEIVED LOUDNESS AND/OR THE PERCEIVED SPECTRAL BALANCE OF AN AUDIO SIGNAL and International Patent Application No. PCT/US20075/007946 published as WO 2007120453 titled CALCULATING AND ADJUSTING THE PERCEIVED LOUDNESS AND/OR THE PERCEIVED SPECTRAL BALANCE OF AN AUDIO SIGNAL. Each of these applications designates the United States. The contents of each of such patent applications published as WO 2006047600 and WO 2007120453 are incorporated herein by reference. See also Alan Seefeldt: “Loudness Domain Signal Processing,” paper 7180 , Proceedings,  123 rd Convention of the Audio engineering Society , New York, N.Y., USA, 5-8 Oct. 2007. 
     The above-mentioned Seefeldt publications described audio signal quality enhancement signal processing methods that occur in what is called the perceptual domain. PDEQ processing methods include determining modification parameters from calculations carried out in a perceptual domain, and modifying audio signal data according to the modification parameters. By determining the modification parameters in the perceptual domain, greater control over perceptual loudness and perceived spectral balance may be achieved than if such modification parameters were derived in the electrical signal domain. In some embodiments, a basilar-membrane simulating psychoacoustic filterbank or its equivalent is used for performing loudness domain calculations. This can provide a more detailed control of the perceived spectrum than in arrangements that derive modification parameters in the electrical signal domain. 
     Processing in a Perceptual Domain 
     Often, an audio signal is expected to be reproduced at a specified reference level. However, many times, the media data is played back at reduced levels. It is known that there is variation in the perception of audio depending on the reproduction level. Such variation is related to psychoacoustics and the equal loudness contours and the threshold of hearing in quiet. Altered playback levels can result in dramatic differences in timbre and spatial perception of the audio when compared to the same media data played back at reference level. The perceptual domain dynamic equalization as described in embodiments of the present invention includes determining and adjusting the perceived loudness of an audio signal in an improved manner. A psychoacoustic model is used to calculate a measure of the loudness of an audio signal in perceptual units. Such perceptual domain loudness measure is referred to as specific loudness, and is a measure of perceptual loudness as a function of frequency and time. As one example, a dynamic equalization process includes determining parameters in a perceptual domain includes using a signal processing method to compute frequency and time-varying multiplicative gains, which, when applied to the audio, results in the spectral properties of the gain-modified audio being closer to a preset or user defined equalization or spectral balance profile. The gain adjusting methods also include signal processing methods that analyze and modify the audio depending on playback level restoring it to the way it would be perceived at the reference playback level having the preset or user defined equalization. 
     Because specific loudness is a measure of perceptual loudness of an audio signal as a function of frequency and time, in order to process a signal so that its spectral properties become closer to a substantially time invariant shape, the spectrum of the to-be-modified audio signal is generated by smoothing the specific loudness of the signal over time. 
     To reduce the difference between the specific loudness of the audio signal and the target specific loudness, the modifying typically modifies the audio signal as a function of both time and frequency. In the case of a time- and frequency-varying scale factor, the specific loudness may be scaled by the ratio of a measure of a desired spectral shape to the measure of a spectral shape of the audio signal. Such a scaling may be used to transform the perceived spectrum of the audio signal from a time-varying perceived spectrum to be closer to a substantially time-invariant perceived spectrum. When the specific loudness is scaled by the ratio of a measure of a desired spectral shape to the measure of a spectral shape of the audio signal, such a scaling may be usable as a perceptual domain dynamic equalizer. 
     One version of PDEQ includes processing each of a plurality of frequency bands by time varying gain factors that are determined from characteristics in the perceptual loudness domain. As discussed in WO 2006047600 and WO 2007120453, and for aspects of the present invention, a time sampled audio signal denoted x[n], where n is an integer sample index is pre-processed to generate a time-varying spectrum denoted by a function L[b,t], indicating a signal level denoted L within a plurality of frequency bands (critical bands), e.g., 40 bands, each denoted by a band number denoted by integer b varying over time blocks each time block denoted by an integer t. The function L[b,t] of the audio signal may be generated in a number of ways, but advantageously the bands b are spaced to simulate the frequency resolution of human hearing. The goal of PDEQ processing is to modify x[n] so that the modified audio more closely matches a desired time-invariant perceptual domain spectral shape that is specified across bands b by a quantity denoted EQ[b]. 
     In the perceptual domain, starting with the audio signal samples x[n], a quantity called an excitation signal denoted E[b,t] is computed that approximates the distribution of energy along the basilar membrane of the inner ear of a human at a critical frequency band b during a time block t. While other transforms, such as the modified discrete cosine transform (MDCT) also may be used, the perceptual domain excitation may be achieved efficiently by computing the running Short-Time Discrete Fourier Transform (STDFT) of the audio signal denoted x[n], n=0, . . . , N−1, the STDFT denoted by X[k,t], k=0, 1, . . . N−1, and is computed with half overlap and window denoted w[n] according to: 
     
       
         
           
             
               
                 
                   
                     
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     The excitation in some embodiments is computed according to: 
                     E   ⁡     [     b   ,   t     ]       =       ∑     k   =   0       N   -   1       ⁢              T   ⁡     [   k   ]            2     ⁢              C   b     ⁡     [   k   ]            2     ⁢            X   ⁡     [     k   ,   t     ]            2                 (   2   )               
where T[k] represents the frequency response of a filter simulating the transmission of audio through the outer and inner ear of a human, and C b  [k] are a selected set of bandpass filters. In one embodiment, the set of bandpass frequency responses C b  [k] be advantageously chosen to mimic the critical band filtering observed along the basilar membrane in the human ear at critical frequency b. As discussed in WO 2006047600 and WO 2007120453, these filters exhibit an approximately rounded exponential shape and are spaced uniformly on the Equivalent Rectangular Bandwidth (ERB) scale. Example embodiments of the present invention use set of filters with a spacing of 1 ERB, resulting in a total of 40 bands.  FIG. 1  depicts a suitable set of filters with a spacing of 1 ERB, resulting in a total of 40 bands.
 
     The specific loudness denoted N[b,t] is a spectral representation meant to simulate the manner in which a human perceives audio as a function of frequency and time. As described in WO 2006047600 and WO 2007120453, the specific loudness in general as a transformation denoted by Ψ{ }, such that
 
 N[b,t]=Ψ{E[b,t]}.   (3)
 
PDEQ Processing
 
     A PDEQ process computes a measured spectrum in the perceptual domain and modifies the signal such that a desired shape spectral denoted by Eq[b] is achieved. A multi-band perceptual-domain loudness is denoted by L p [b,t], and is a function of the input audio signals specific loudness N[b,t]. While one simple embodiment sets L p [b,t] to be the specific loudness N[b,t], in some embodiments, in order to avoid instability of the processing over time segments t, the specific loudness N[b,t] is first smoothed over time, e.g., uses a single smoothing coefficient λ to provide the smoothed specific loudness denoted  N [b,t] as:
 
   N [b,t]= 2 N[b,t− 1]+(1−λ) N[b,t].   (4)
 
     Note that, as described in WO 2006047600 and WO 2007120453, alternate embodiments might include smoothing the excitation rather than the specific loudness, in which case, the smoother excitation denoted Ē[b,t] is given by:
 
 Ē[b,t]=λE[b,t− 1]+(1−λ) E[b,t],   (5)
 
     and Eqn. 3 for the specific loudness becomes:
 
 N[b,t]=Ψ{Ē[b,t]}   (6)
 
     Other embodiments can use different smoothing methods, for example, including a recursive relation involving more than just the most previous time&#39;s smoothed specific loudness  N [b,t−1] in the case of smoothing the specific loudness, or previous time&#39;s smoothed excitation Ē[b,t−1] in the case of smoothing the excitation. Furthermore, the multi-band loudness (the spectrum), L p  [b,t] may be calculated by smoothing the specific loudness N[b,t] across bands so that there is not a drastic change from one band to the next. In the case of using the smoothed specific loudness, the result is a band-smoothed loudness denoted  L   p [b,t] with a smoothing filter is applied: 
     
       
         
           
             
               
                 
                   
                     
                       
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     where Q(b) is a band smoothing filter. 
     To preserve the original dynamic range of the audio signal, the desired spectral shape EQ[b] may be normalized to have the same overall level as the smoothed signal loudness denoted  L   p [b,t] to generate a normalized spectral shape denoted EQ NORM [b,t] as: 
     
       
         
           
             
               
                 
                   
                     
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     The processing is to modify the specific loudness N[b,t] to achieve a target specific loudness denoted {circumflex over (N)}[b,t] such that the resulting spectral shape is closer to the desired shape EQ[b]. Again, letting the function Ψ{·} denote the non-linear transformation from excitation to specific loudness, i.e., N[b,t]=Ψ{E[b,t]}, where the excitation may be the smoothed excitation, one embodiment determines a set of time varying multi-band gains G p  [b,t] forming a time varying filter according to the relationship.
 
 {circumflex over (N)}[b,t]=Ψ{G   p   2   [b,t]E[b,t]},   (9)
 
     where E[b,t] is in one embodiment the smoothed excitation. 
     The gains G p [b,t] are applied in the frequency domain to a delayed version of X[k,t] that is obtained by the STDFT (or MDCT), where the delay is to account for the time needed to compute the gains. The resulting gain multiplied signal:
 
 {circumflex over (X)}[k,t]=G   p   [k,t]X[k,t−d] 
 
     where d denotes the delay time, is then applied to a set of synthesis filters, denoted S b [k] for frequency band b to generate a signal denoted {circumflex over (X)}[k,t] where 
     
       
         
           
             
               
                 
                   
                     
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     Solving for the gains can take on many forms. If the inverse Ψ −1 {·} of the transformation Ψ{·} exists, then 
     
       
         
           
             
               
                 
                   
                     
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                           ] 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
     where the excitation may be the smoothed excitation. If a closed form of Ψ −1 {·} does not exist, then the gains may be solved for by an iterative method, or by pre-computing Ψ{·} and using table look-up. 
     As described in WO 2006047600 and WO 2007120453, for perceptual domain dynamic equalization, the target specific loudness is related to the specific loudness by: 
     
       
         
           
             
               
                 
                   
                     
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                       ⁡ 
                       
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                           , 
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                         ] 
                       
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     where β is a user-specified parameter ranging from zero to one, indicating the degree of PDEQ processing that is to be applied to the audio signal. Note that 
     
       
         
           
             
               
                 
                   
                     Ψ 
                     ⁢ 
                     
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                               ] 
                             
                           
                           
                             
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                           NORM 
                         
                         ⁡ 
                         
                           [ 
                           
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                             b 
                             , 
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                           ] 
                         
                       
                       } 
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
     from which the gains G p [b,t] may be determined. 
     From Eqn. 12, one notes that when β=0,{circumflex over (N)}[b,t]=N[b,t] for all bands b and therefore the original signal is unmodified. When β=1, the scaling of the desired to actual specific loudness is equal to the ratio of the normalized desired specific loudness shape to the smoothed signal specific loudness spectrum, thereby transforming the smoothed spectral shape of the original audio signal completely to that of the desired shape EQ[b], expressed in the perceptual domain. In such a case, 
     
       
         
           
             
               Ψ 
               ⁢ 
               
                 { 
                 
                   
                     
                       G 
                       p 
                       2 
                     
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                     ⁡ 
                     
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                         b 
                         , 
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                 } 
               
             
             = 
             
               
                 
                   
                     EQ 
                     NORM 
                   
                   ⁡ 
                   
                     [ 
                     
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                     ] 
                   
                 
                 
                   
                     
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                       _ 
                     
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                     ] 
                   
                 
               
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               ⁢ 
               
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                     ] 
                   
                 
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     from which the gains G p [b,t] may be determined. 
     A PDEQ Processing Example 
       FIG. 2A  shows a simplified block diagram of a feed-forward embodiment of a PDEQ apparatus in which pre-processing separates an input audio signal into frequency bands. In practical embodiments, the processing of the audio is carried out in the digital domain, so that sampling and digitizing of analog signals is carried out. Such details are left out of this description, and would be clear to those skilled in the art. 
     The apparatus of  FIG. 2A  may be included, for example, in a media device or some other audio device for playing back audio. An apparatus that processes audio signals, such as a media device, is called an audio signal processing apparatus herein. 
     The arrangement shown in  FIG. 2A  is used to carry out PDEQ as described above, e.g., in Eqns. 1 through 13, with the addition of a control interface including a control interface with one or more control elements configured to accept a user input for specifying the equalization, as described in more detail herein below. 
     The term “control interface” is used herein for describing the combination of the visual or tactile presentation to a user of one or more control elements configured to accept a user input via one or more input mechanism. The control elements thus can be manipulated via respective input mechanisms. The term “input mechanism” of course should not be taken to only suggest only physical mechanical control, but also to include any agency or means by which input is provided by a user. Thus, the control element may include “virtual” controls such as virtual knobs, sliders, touch pads, and so forth, that include a display and some manner of accepting user input (the input mechanism) to manipulate the virtual control(s). Thus, in some embodiments, the control interface includes a user interface of one or more control elements displayed on a display device, and a user input method or device or subsystem for accepting user input of one or more of the displayed control elements. In other embodiments, the control interface includes physical control elements that can be manipulated by the user to provide the user input, e.g., one or more knobs, one or more slide controls, and/or one or more two dimensional controls such as a touch pad configured to accept a user indication of a location on the touch pad. 
     The Audio  201  first passes through an analysis filterbank function or device  203 , which splits the audio signal into a plurality of frequency bands denoted by frequency index b. Thick lines in  FIG. 2A  indicate multiple signals, so that there are multiple outputs, each a frequency band b from analysis filterbank  203 . Each of these frequency bands undergoes the processing steps shown in  FIG. 2A , up to a synthesis filterbank  223 , which sums the bands to a combined wideband signal to generate the modified audio signal  225 . 
     The response of the filter associated with each frequency band in the analysis filterbank  203  is designed to simulate the response at a particular location of the basilar membrane in the inner ear of a human. In some embodiments, analysis filterbank  203  includes a set of linear filters whose bandwidth and spacing are constant on the equivalent rectangular bandwidth (ERB) frequency scale. See  FIG. 1 . 
     Analysis filterbank  203  may be implemented efficiently through use of the forward and/or inverse short-time discrete Fourier transform (short-time DFT, STDFT) or the forward and/or inverse modified discrete cosine transform (modified DCT, MDCT). The forward and/or inverse STDFT or MDCT may be used similarly to implement synthesis filterbank  223 . 
     The output of each filter in the analysis filterbank  203  next passes into a transmission filter function or device  205  that is designed to simulate the filtering effect of the transmission of audio through the outer and middle ear of a human. 
     In order to compute the loudness of the input audio signal, a measure of the audio signals&#39; short-time energy in each filter of the analysis filterbank  203  after application of the transmission filter  205  is obtained. This time and frequency varying measure is referred to as the excitation, denoted E[b,t], where b denotes the frequency band, and t is an index denoting blocks of time. To obtain the excitation, the outputs of transmission filter  205  are accepted by an excitation function or device  207 , the outputs of which are designed to simulate the distribution of energy along the basilar membrane of a human ear. Depending on the desired effects, the excitation energy values may be smoothed across time by a smoothing function or device  209  that are configured to have time constants set in accordance with the requirements of the desired effects of the processing. The output of excitation function  207  is a frequency domain representation of energy denoted E in respective ERB bands denoted b per time denoted t. 
     A specific loudness function or device  211  converts the smoothed excitation signals into specific loudness (SL). Specific loudness may be represented, e.g., in units of sone per unit frequency, e.g., sone per ERB. Note that from the specific loudness, the overall or total loudness is the sum of the specific loudness across all bands b. Designing the specific loudness function  211  includes determining gains for narrowband and wideband estimated values chosen to match experimental data on the growth of loudness for tones and noise. Furthermore, the specific loudness function  211  is designed such that the specific loudness is some small value instead of zero when the excitation is at the threshold of hearing, and such that the specific loudness decreases monotonically to zero as the excitation decreases to zero. 
     The specific loudness components associated with the frequency bands are passed into a dynamic equalization specific loudness modification function or device  213  that generates a target specific loudness. In the case of perceptual domain dynamic equalization (PDEQ), a target specific loudness may be calculated using a relationship that takes into account the current spectrum of the audio, in particular, the spectrum of the signal is measured and the signal is then dynamically modified in order to transform the measured spectrum closer to an essentially static desired shape, specified across bands b and referred to as EQ[b]. The spectral shape of the audio signal is denoted by L[b,t], and in one embodiment, is determined as a smoothing of the specific loudness, denoted N[b,t] across time. One may not want the PDEQ modification to vary drastically from one band to the next, and therefore a band-smoothing function may be applied to generate a band-smoothed spectrum. In order to preserve the original dynamic range of the audio, the desired spectrum EQ[b] may be normalized to have the same overall loudness as the measured spectral shape given by L[b,t]. 
     In embodiments described herein a target EQ specification function or device  217  is used to provide a control interface to a user in order for the user to specify one or more parameters for the dynamic equalization using one or more respective control elements. The target EQ specifier  217  may include a capture function by which the specific loudness of some audio that has desired properties is captured, e.g., from the specific loudness block  211  while the input  201  is audio with desired characteristics. This provides the desired characteristics EQ[b], which may be stored. In the case there is one EQ[b], the user specified parameter is denoted as β in Eqn. 12 and is a parameter that varies from 0 to 1 that expresses the amount of PDEQ that is to be applied, with a value 0 indicating no PDEQ. 
     Taking as its inputs the smoothed excitation frequency band components from smoother  209  and the target specific loudness from the SL modification  213 , a gain solver function or device  215  is configured to determine the gains that needs to be applied to each band b in order to transform the determined specific loudness N[b,t] into the target specific loudness {circumflex over (N)}[b,t]. The gains determined are in general frequency- and time-varying gains, which, when applied to the original excitation, result in a specific loudness that, ideally, is equal to the desired target specific loudness, and in practice results in modifying the audio signal in order to reduce the difference between its specific loudness and the target specific loudness. The gain solver  215  may be implemented in various ways. If a closed form calculations is possible, it is applied. If a table lookup is possible, such a method also may be used. In one embodiment, the gain solver may include an iterative process in which, for each iteration, a specific loudness is evaluated using a current estimate of the gains. Other methods for computing the modification parameters through either explicit or implicit computation of the specific loudness and target specific loudness may be devised, and this invention is intended to cover all such methods. 
     The gains per band generated by the gain solver  215  may be smoothed further over time by optional smoothing function or device  219  in order to minimize perceptual artifacts. It may alternately be advantageous that temporal smoothing be applied elsewhere in the overall process or device. 
     Finally, the gains determined by gain solver  215  are applied to respective bands through a respective multiplicative combining function or combiner  221  that applies the gains to the outputs from the analysis filterbank delayed by a suitable delay function or device  204  configured to compensate for any latency associated with the gain computation. 
     The modified audio  225  is synthesized from the gain-modified bands in a synthesis filterbank function or device  223 . As described above, analysis filterbank  203  may be implemented efficiently through use of the short-time DFT or the modified DCT, and the STDFT or MDCT may be used similarly to implement synthesis filterbank  223 . The synthesis filters for the bands are determined from the filters used in analysis filterbank  203  and the delay of delay  204 . 
     Note that alternatively, instead of calculating gains for use in applying gain modifications in frequency bands, the gain solvers  215  may calculate filter coefficients that control a time-varying filter, such as a multi-tapped FIR filter or a multi-pole IIR filter. For simplicity in exposition, aspects of the invention are mainly described as employing gain factors applied to frequency bands, it being understood that filter coefficients and time-varying filters may also be used in practical embodiments. 
     Approximately Perceptual Dynamic Equalization 
     While some embodiments of the invention are for perceptual domain dynamic equalization (PDEQ), as described above, aspects of the invention are applicable also to what we call approximate perceptual dynamic equalization, or simply dynamic equalization (DEQ) herein, in which a spectral loudness measure denoted L[b,t] as a function of frequency band and time is an approximation to the specific loudness L p [b,t]. 
     For this approximation, the measure of loudness, also called the signal spectrum, is taken to be 
     
       
         
           
             
               
                 
                   
                     
                       L 
                       ⁡ 
                       
                         [ 
                         
                           b 
                           , 
                           t 
                         
                         ] 
                       
                     
                     = 
                     
                       
                         ∑ 
                         
                           k 
                           = 
                           0 
                         
                         
                           N 
                           - 
                           1 
                         
                       
                       ⁢ 
                       
                         
                           
                              
                             
                               
                                 C 
                                 b 
                               
                               ⁡ 
                               
                                 [ 
                                 k 
                                 ] 
                               
                             
                              
                           
                           2 
                         
                         ⁢ 
                         
                           
                              
                             
                               X 
                               ⁡ 
                               
                                 [ 
                                 
                                   k 
                                   , 
                                   t 
                                 
                                 ] 
                               
                             
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                           2 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
           
         
       
     
     where again C b [k] are a selected set of bandpass filters that in one embodiment, are chosen to mimic the critical band filtering observed along the basilar membrane in the human ear at critical frequency b, and where X[k,t], k=0, 1, . . . N−1, are a set of STDFT (or MDCT) coefficients determined with an overlap window, as is known to those skilled in the art. 
     Comparing Eqn. 14 to Eqns. 2 and 3, the loudness measure L[b,t] is an approximation of the excitation E[b,t], the approximation being that the filter T[k] representing the frequency response of a filter simulating the transmission of audio through the outer and inner ear of a human has constant magnitude for all k. Furthermore, the loudness spectral measure L[b,t] an be considered an approximation to the specific loudness with the function Ψ{·} being the identity function such that Ψ{L[b,t]}=L[b,t]. Hence performing DEQ with such a loudness measure can be considered approximately perceptual DEQ. 
     For approximately perceptual DEQ, a set of time varying multi-band gains G[b,t] forming a time varying filter according to the relationship is applied according to the relationship:
 
 {circumflex over (L)}[b,t]=G   2   [b,t]L[b,t].   (15)
 
     is applied to the original signal spectrum L[b,t], resulting in a transformed spectral loudness measure denoted {circumflex over (L)}[b,t] whose spectral shape is closer to the desired shape denoted, as before, by EQ[b]. Eqn. 15 is analogous to Eqn. 9, the latter being for PDEQ. 
     In some embodiments, for DEQ, the filter gains G[b,t] are computed by comparing the spectral shape of the original signal L[b,t] to the desired shape EQ[b]. To prevent the filter G[b,t] from varying too fast over time and causing artifacts in the processed audio, the signal spectrum, i.e., the approximate loudness measure L[b,t] may first be smoothed across time in each band b using a smoothing coefficient denoted λ:
 
   L [b,t]=λ  L [b,t− 1]+(1−λ) L[b,t].   (16)
 
     In alternate embodiments, different smoothing methods may be used. 
     As in the case, of PDEQ, for DEQ, to preserve the original dynamic range of the audio signal, the desired spectral shape EQ[b] may be normalized to have the same overall level as the smoothed signal spectrum  L [b,t]: 
     
       
         
           
             
               
                 
                   
                     
                       EQ 
                       NORM 
                     
                     ⁡ 
                     
                       [ 
                       
                         b 
                         , 
                         t 
                       
                       ] 
                     
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             ∑ 
                             c 
                           
                           ⁢ 
                           
                             
                               L 
                               _ 
                             
                             ⁡ 
                             
                               [ 
                               
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                                 , 
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                               ] 
                             
                           
                         
                         
                           
                             ∑ 
                             c 
                           
                           ⁢ 
                           
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                             ⁡ 
                             
                               [ 
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                               ] 
                             
                           
                         
                       
                       ) 
                     
                     ⁢ 
                     
                       EQ 
                       ⁡ 
                       
                         [ 
                         b 
                         ] 
                       
                     
                   
                 
               
               
                 
                   ( 
                   17 
                   ) 
                 
               
             
           
         
       
     
     The filter G 2  [b,t] is computed from the ratio of the normalized spectral shape EQ NORM [b,t] and the smoothed signal spectrum  L [b,t]: 
                         G   2     ⁡     [     b   ,   t     ]       =         (         L   _     ⁡     [     b   ,   t     ]           EQ   NORM     ⁡     [     b   ,   t     ]         )       1   -   β       ⁢         EQ   NORM     ⁡     [     b   ,   t     ]           L   _     ⁡     [     b   ,   t     ]             ,           (   18   )               
where β is a user-specified parameter ranging from zero to one, indicating the degree of DEQ processing that is to be applied to the audio. Analyzing Eqn. 18, one notes that when β=0, the filter G[b,t] equals one for all bands b and therefore the original signal is unmodified. When β=1, the filter is equal to the ratio of the normalized desired shape to the smoothed signal spectrum, thereby transforming the smoothed spectral shape of the original audio completely to that of the desired shape EQ[b].
 
       FIG. 2B  shows a simplified block diagram of a feed-forward embodiment of a DEQ apparatus in which pre-processing separates an input audio signal into frequency bands. In practical embodiments, the processing of the audio is carried out in the digital domain, so that sampling and digitizing of analog signals is carried out. Such details are left out of this description, and would be clear to those skilled in the art. 
     As in the case of  FIG. 2A , the apparatus of  FIG. 2B  may be included, for example, in a media device or some other audio device for playing back audio. An apparatus that processes audio signals, such as a media device, is called an audio signal processing apparatus herein. 
     The arrangement shown in  FIG. 2B  is used to carry out DEQ as described above, e.g., in Eqns. 14 through 18, with the addition of a control interface including a control interface with one or more control elements configured to accept a user input for specifying the equalization, as described in more detail herein below. 
     The Audio  201  first passes through an analysis filterbank function or device  203 , which splits the audio signal into a plurality of frequency bands denoted by frequency index b. Thick lines in  FIG. 2B  indicate multiple signals, so that there are multiple outputs, each a frequency band b from analysis filterbank  203 . Each of these frequency bands undergoes the processing steps shown in  FIG. 2B , up to a synthesis filterbank  223 , which sums the bands to a combined wideband signal to generate the modified audio signal  225 . Analysis filterbank  203  and synthesis filterbank  223  in  FIG. 2B  can be substantially as in  FIG. 2A . 
     The output of each filter in the analysis filterbank  203  is used to determine in spectral measure determiner  231  the spectral measure of loudness, denoted L[b,t], where b denotes the frequency band, and t is an index denoting blocks of time. The spectral measure determiner  231  is in one embodiment substantially the same as element  207  of  FIG. 2A . Depending on the desired effects, the spectral measure L[b,t] energy values may be smoothed across time by a smoothing function or device  233  that is configured to have time constants set in accordance with the requirements of the desired effects of the processing. 
     The smoother loudness measure from smoothing device  233  and an essentially static desired spectral shape, specified across bands b and referred to as EQ[b] and used to generate a set of gains by a gain solver  237  as described in above in Eqns. (17) and (18). 
     In embodiments described herein a target EQ specification function or device  235  is used to provide a control interface to a user in order for the user to specify one or more parameters for the dynamic equalization using one or more respective control elements. The target EQ specifier  235  may include a capture function by which the spectral content L of some audio that has desired properties is captured, e.g., from the spectral measure block  231  or smoothing block  233  while the input  201  is audio with desired characteristics. This provides the desired characteristics EQ[b], which may be stored. In the case there is one EQ[b], the user specified parameter is denoted β as in Eqn. 18 and is a parameter that varies from 0 to 1 that expresses the amount of DEQ that is to be applied, with a value 0 indicating no DEQ. 
     The gains determined are in general frequency- and time-varying gains, which, when applied to the spectral measure, result in a spectral measure that, ideally, is equal to the desired target spectral measure EQ[b], and in practice results in modifying the audio signal in order to reduce the difference between the spectral measure of the signal and the target spectral measure EQ[b]. The gain solver  237  may be implemented in various ways. 
     The gains per band generated by the gain solver  237  may be smoothed further over time by optional smoothing function or device  239  in order to minimize perceptual artifacts. It may alternately be advantageous that temporal smoothing be applied elsewhere in the overall process or device. 
     Finally, the gains determined by gain solver  237  are applied to respective bands through a respective multiplicative combining function or combiner  221  that applies the gains to the outputs from the analysis filterbank delayed by a suitable delay function or device  204  configured to compensate for any latency associated with the gain computation. 
     The modified audio  225  is synthesized from the gain-modified bands in a synthesis filterbank function or device  223 . The synthesis filters for the bands are determined from the filters used in analysis filterbank  203  and the delay of delay  204 , and otherwise are as described with reference to  FIG. 2A . 
     Note that alternatively, instead of calculating gains for use in applying gain modifications in frequency bands, the gain solvers  237  may calculate filter coefficients that control a time-varying filter, such as a multi-tapped FIR filter or a multi-pole IIR filter. For simplicity in exposition, aspects of the invention are mainly described as employing gain factors applied to frequency bands, it being understood that filter coefficients and time-varying filters may also be used in practical embodiments. 
     An Apparatus with a Processing System 
       FIG. 3  shows a simplified block diagram of one apparatus embodiment for processing audio  201  to generate audio output  325  that has been modified by DEQ or PDEQ as specified in accordance to one or more features of the present invention. The apparatus, for example, can implement PDEQ processing such as described by Eqns. 1 to 134, or DEQ processing such as described by Eqns. 14 to 18. Such an apparatus may be included, for example, in a media device for playback of audio media. The audio input  201  and the audio output  325  are assumed to be in the form of sampled data. In the case of analog input, a digitizer including an analog to digital converter and quantizer would be present. For audio playback, a de-quantizer and a digital-to-analog converter would be present. Such and other elements that might be included in a complete audio processing system, e.g., media device are left out, and how to include such elements would be clear to one skilled in the art. The embodiment shown in  FIG. 3  includes a processing system  303  that is configured in operation to carry out the PDEQ or DEQ methods described herein, including specifying the desired equalization via one or more of the control interface embodiments described herein. The processing system  303  includes at least one processing units (processors)  305 , which can be the processing units of a digital signal processing device, or a CPU of a more general purpose processing device. The processing system  303  also includes a storage subsystem  307  typically including one or more memory elements. In one embodiment, the processing system  303  further includes a control interface that includes a user interface display  315  for displaying a user interface to a user, and at least one control element  317  configured to accept a user input and coupled to the user interface display. The elements of the processing system are coupled, e.g., by a bus subsystem or some other interconnection mechanism not shown in  FIG. 3 . Some of the elements of processing system  303  may be integrated into a single circuit, using techniques common skilled in the art. 
     The storage subsystem  307  includes instructions  311  that when executed by the processing unit or units  305 , cause carrying out of the methods described herein. 
     In some embodiments, the storage subsystem  307  is configured to store one or more target spectral characteristics  313  used, in conjunction with the control elements, to accept user input to specify the DEQ or PDEQ processing carried out by the processing system  303 . 
     The system shown in  FIG. 3  can be incorporated in a specialized device such as a portable media player. The system also can be part of a general purpose computer, e.g., a personal computer configured to process audio signals. 
     Interacting with a DEQ Processing System or Device 
     In the remainder of this description, by dynamic equalization is meant either perceptual domain dynamic equalization (PDEQ), or the broader not necessarily perceptual domain perceptual dynamic equalization (DEQ) in which the time varying spectrum of an input signal is modified to more closely resemble a time invariant spectral profile, called a “DEQ preset spectral profile” and denoted EQ[b] herein, for both the cases of perceptual DEQ processing and other DEQ processing. In general, the term DEQ processing will be understood to mean either perceptual DEQ, e.g., per Eqns. 1 to 13, or DEQ which is not necessarily purely perceptual, e.g., per Eqns. 14 to 18. 
     A Single Selected DEQ Preset Spectral Profile 
     One feature of embodiments of the present invention includes a method and apparatus for a user to interact with a DEQ processing system or device. Such interactions including presenting a control interface to a user, and accepting settings by the user of control elements in the control interface. For example, the system shown in  FIG. 3  includes a graphical user interface  315  for presenting controls, and at least one control element configured to accept a user input. Alternate embodiments for the control interface can include traditional components such as knobs, sliders, and so forth. 
     In one set of embodiments, the existence of a DEQ preset spectral profile EQ[b] and the variable degree of DEQ processing β provides a simple parameter that allows a user of a media device such as implemented in  FIG. 3  unprecedented control over the perceived spectrum of an audio signal.  FIGS. 4A and 4B  each shows a control interface—a slider in  FIG. 4A , and a rotary knob in FIG.  4 B—for controlling the amount of DEQ processing according to a DEQ preset spectral profile EQ[b]. The DEQ preset spectral profile EQ[b] stored, e.g., as one of a set of stored DEQ preset spectral profiles. The user selected a particular DEQ preset spectral profile EQ[b] and selects the amount of DEQ to apply according to the position of the DEQ controller. The slider or knob position is accepted and, in some embodiments, perceptual DEQ processing is applied to an audio signal according to Eqns. 8, 12, and 13, or in other embodiments, DEQ processing according to Eqns. 17 and 18. That is, for the case of perceptual DEQ, the preset specific loudness and the gains are determined according to Eqns. 8, 12 and 13. The audio is processed according to the determined multi-band gains. 
     In  FIG. 4A  the DEQ controller is a standard slider which controls the amount of DEQ applied, where DEQ=0% corresponds to β=0 and DEQ=100% corresponds to β=1. Similarly, the same user control could be provided through the use of a standard rotary controller (knob) as shown in  FIG. 4B . In the application shown in  FIGS. 4A and 4B , when DEQ is set to 0%, no processing of the audio signal takes place and as the amount of DEQ applied is increased to 100%, the full spectral processing is applied to the input audio signal. 
     Note than when implemented on a processing system such as shown in  FIG. 3 , the DEQ control interface of FIGS.  4 A, 4 B include a virtual slider ( FIG. 4A ) or a virtual knob ( FIG. 4B ) rendered on a graphical user interface display  315 . Thus, the control elements include one or more virtual or actual slider controls or one or more virtual or actual rotary controls. 
     Multiple Preset Spectral Profiles 
     As described above, some embodiments of the DEQ processing system include the ability to store a plurality of preset spectral profiles. Each of these may be recalled by a user. These DEQ preset spectral profiles may be preconfigured, e.g., by a manufacturer. Some embodiments also include the ability for a spectral profile to be captured by a user using a DEQ equalization profile capture function in the target EQ specifier  217  (see, e.g.,  FIG. 2 ). Such capture includes capturing the output of specific loudness block  211  when the input  201  is audio that has desired properties. 
     Thus, in some embodiments, the control interface includes at least one control element for selecting one or more DEQ preset spectral profiles from a set of DEQ preset spectral profiles. 
     The existence of multiple DEQ preset spectral profiles stored in a system allows additional manipulation and control of the perceived spectrum of an audio signal. A relatively unsophisticated user can achieve relatively sophisticated equalization. 
     Control Between a Pair of Preset Spectral Profiles 
       FIGS. 5A and 5B  each shows a control interface—a simple slider control in  FIG. 5A  and a simple knob control in FIG.  5 B—that is manipulated by a user to select DEQ between two DEQ preset spectral profiles denoted EQ 1 [b] and EQ 2  [b]. In some embodiments, the control interface includes at least one control element for selecting two preset spectral profiles, and a control element (the slider or knob) for setting a parameter we call the preset morphing parameter (also called the preset blending parameter) in order to determine a blending of the two DEQ preset spectral profiles for the audio output. The selecting of the two DEQ preset spectral profiles is from a set of DEQ preset spectral profiles, e.g., stored, pre-defined DEQ preset spectral profiles that were selected in the factory by the manufacturer, or DEQ preset spectral profiles that were obtained by capture, or otherwise. The two DEQ preset spectral profiles EQ 1 [b] and EQ 2 [b] are used as the limits on either end of the DEQ controller. The slider or knob sets the preset morphing parameter, denoted α, 0≦α≦1, such that the EQ[b] applied in some perceptual DEQ processing embodiments according to Eqns. 8, 12, and 13, or in other DEQ processing embodiments, according to Eqns. 17 and 18, is a linear combination of the two DEQ preset spectral profiles determined by the parameter α.
 
EQ[b]=α·EQ 2   [b ]+(1−α)·EQ 1   [b]   (19)
 
     In one embodiment, the parameter β in Eqn. 12 or Eqn. 18 is set to a fixed value of 1. In an alternate embodiment, an additional control interface, e.g., an additional slider or knob is provided to the user to select the parameter β. 
     As shown in  FIGS. 5A and 5B , when the slider is set to the bottom position, or α=0 then the audio signal is fully processed using DEQ preset spectral profile EQ 1  [b]. As the slider is moved and the value of α increased, the applied DEQ preset spectral profile applied is a combination of the two DEQ preset spectral profiles EQ 1 [b] and EQ 2  [b] until the value of α is increased to its full value of 1 when the DEQ preset spectral profile applied is fully EQ 2 [b]. 
     One embodiment includes selecting the preset spectral profiles such that EQ 1 [b] is designed to boost bass frequencies and EQ 2  [b] is designed to boost treble frequencies. With such an embodiment, the control interface provides a content aware version of what is commonly called a tone control. Another embodiment includes selecting EQ 1 [b] designed to reduce the response to bass and treble frequencies, i.e., to provide a bass and treble cut, and selecting EQ 2  [b] to increase the response to bass and treble frequencies, i.e., to provide a bass and treble boost such that the control interface provides what is commonly called a loudness control in traditional audio systems, but carried out in a audio signal content aware manner. Of course, in some embodiments, two controls are included, one providing content aware tone control, and the other providing content aware loudness control. 
     While Eqn. 19 shows linear morphing between two DEQ preset spectral profiles denoted according to a linear transformation, the invention is not limited to such morphing by linear transformation. Alternate embodiments include morphing according to a different, e.g., non-linear transformation such as a logarithmic transformation. In yet another embodiment, a look-up table rather than a calculation is used to determine EQ[b]. 
     In some embodiments, the control interface includes an additional control element configured to control the amount of DEQ processing to apply using the blended two DEQ preset spectral profiles of Eqn. 19. 
     Control Between More than Two Preset Spectral Profiles 
     The control interface for DEQ processing shown in  FIGS. 5A and 5B  can easily be expanded to include the control and application of more than two DEQ preset spectral profiles.  FIGS. 6A and 6B  each shows a control interface that addresses the application and control of three different DEQ preset spectral profiles—using a slider in the case of  FIG. 6A , and a knob in  FIG. 6B . 
     In this usage scenario, a user selects three or more DEQ preset spectral profiles, e.g., three DEQ preset spectral profiles denoted EQ 1 [b], EQ 2 [b], and EQ 3 [b] from a set of DEQ preset spectral profiles that may be factory defined. The control allows a user to determine a DEQ preset spectral profile that morphs between pairs of the three or more selected DEQ preset spectral profiles. The three or more selected DEQ preset spectral profiles are spatially distributed on different positions on the control elements, e.g., slider or knob of the control interface that are configured to accept user input via respective input mechanism(s). The user adjusts the control element to select a blending of a pair of DEQ preset spectral profiles according to the preset blending parameter (also called morphing parameter) denoted α, defined in the case of three selected DEQ preset spectral profiles such that the EQ[b] applied in some perceptual DEQ processing embodiments according to Eqns. 8, 12, and 13, or in other DEQ processing embodiments, according to Eqns. 17 and 18 is set equal to:
 
EQ[b]=2α·EQ 2   [b ]+(1−2α)·EQ 1   [b ] for 0≦α≦0.5  (20)
 
and
 
EQ[b]=2(α−0.5)·EQ 3   [b ]+(1−2(α−0.5))·EQ 2   [b ] for 0.5&lt;α≦1.0  (21)
 
     In some embodiments, the parameter β (as used in Eqn. 12 or Eqn. 18) is set to a fixed value of 1 for full effect. In alternate embodiments, the control interface further includes a control element for controlling the amount of the overall DEQ processing that is applied, e.g., by an additional control interface, e.g., an additional slider or knob is provided to the user to select the parameter β. Thus, the value of β does not need to be fixed at 1, or the same value all the time. The value of β could alter as the selected preset changes. The value of β could also be altered based on the genre of music being played or date of production of a music track being played. 
     It should be reiterated, that instead of a user selecting multiple individual DEQ preset spectral profiles, multiple DEQ preset spectral profiles could be grouped by an audio device manufacturer into meta-DEQ preset spectral profiles to make it easier for the user to interact with the audio device. A user could also create one or more user&#39;s own custom meta-DEQ preset spectral profiles by manually selecting multiple DEQ preset spectral profiles. 
     The order of the DEQ preset spectral profiles from α=0 to α=1 may be determined by a perceptual analysis and ordering of the DEQ preset spectral profiles. For example in  FIGS. 6A and 6B , EQ 1 [b] could be chosen to be a preset that boosts only low frequencies, EQ 2  [b] could be chosen to be a preset that boosts predominantly middle frequencies and EQ 3  [b] could be chosen to be a preset that boosts only high frequencies. In this manner, the one control element can be used to provide an input content aware tone control. 
     While Eqns. 20 and 21 show linear morphing between pairs of DEQ preset spectral profiles according to a linear transformation, the invention is not limited to such morphing by linear transformation. Alternate embodiments include morphing according to a different, e.g., non-linear transformation such as a logarithmic transformation. In yet another embodiment, a look-up table rather than a calculation is used to determine EQ[b]. 
     The use of multiple DEQ preset spectral profiles can easily be expanded to more than the three outlined in  FIGS. 6A and 6B  with their distribution on the α parameter controller being something other than equally distributed. 
     DEQ Control Interface Using a Two-Dimensional Control Element 
     Further embodiments of the invention include a control interface that includes a two dimensional control element configured to accept a user indication of a location on an area defining the two-dimensional control element. Examples of a control interface with a two dimensional control element include a touchpad used to control the cursor found on most computer laptops, a trackball in combination with a displayed two dimensional surface, and a displayed two dimensional surface in a touch sensitive screen. Such control interfaces with two dimensional control elements recently also appear in devices such as cellular telephones and portable media devices. 
     The two-dimensional surface of the two-dimensional control element is called the control surface herein. 
     A two-dimensional control element allows additional powerful control of DEQ preset spectral profiles compared to the one-dimensional control elements described above and in  FIGS. 5A  though  6 B.  FIG. 7  shows a two-dimensional control element, such as a computer touchpad or media device touch sensitive screen, that provides for a user a mechanism to control the type of DEQ applied to an audio signal. An example scenario includes a user selecting four DEQ preset spectral profiles from a set of DEQ preset spectral profiles, or the user selecting a pre-defined set that when selected defines four individual DEQ preset spectral profiles. In the case of a rectangle-shaped two-dimensional control element, the control element is configured such that each corner corresponds to one of the four individual DEQ preset spectral profiles. 
     The control interface is then used to specify the preset EQ[b] that is applied in Eqns. 12—or Eqn, 18 depending on the type of DEQ processing. In some embodiments, bilinear interpolation and the X-Y coordinates of the user specified position are used to interpolate between the four DEQ preset spectral profiles located at the four corners of the two-dimensional control element. 
       FIG. 8  shows the two-dimensional control element of  FIG. 7  with overlaid X-Y coordinate axes that are used to translate the user input position to X-Y values that are used to compute EQ[b]. 
     Denote by EQ 1 [b], EQ 2 [b], EQ 3  [b], and EQ 4 [b] the four DEQ preset spectral profiles of the corners. Then, for the example as shown in  FIG. 8 :
 
EQ[b]=0.25·EQ 1   [b]+ 0.25·EQ 2   [b]+ 0.25·EQ 3   [b]+ 0.25·EQ 4   [b ] for X,Y=0,0  (22)
 
and similarly
 
EQ[b]=EQ 1 [b] for  X,Y=− 1,−1  (23)
 
EQ[b]=EQ 2 [b] for  X,Y= 1,−1  (24)
 
     and so on. 
     The EQ[b] for other X,Y values is the combination obtained by fitting a bilinear surface through existing data points. The value of an interpolated point is a combination of the values of the four closest points EQ 1 [b], EQ 2 [b], EQ 3 [b], and EQ 4 [b]. 
     Alternate embodiments use other processes to compute EQ[b] from the user-indicated X,Y position and the four individual DEQ preset spectral profiles. One alternate embodiment using bi-triangular linear interpolation divides the rectangular area into a pair of triangles, then interpolates linearly within the corresponding triangle. Yet other embodiments use nonlinear combinations. One example of use of a nonlinear combination is to provide finer control in the canter region of the control surface. 
     A two-dimensional control element can be used for control of the application of more than four DEQ preset spectral profiles.  FIG. 9  illustrates a control interface with a two-dimensional control element that provides control between nine DEQ preset spectral profiles denoted EQ 1 [b], EQ 2 [b], EQ 3 [b], EQ 4 [b], EQ 5 [b], EQ 6 [b], EQ 7 [b], EQ 8 [b], and EQ 9 [b]. Such control can of course be expanded to a larger number of DEQ preset spectral profiles used in conjunction with the control interface. As for a one-dimensional controller, the ordering of the DEQ preset spectral profiles, in this case on the two-dimensional control element, can be determined by a perceptual analysis and ordering of the DEQ preset spectral profiles, e.g., by the manufacturer for factory provided DEQ preset spectral profiles, or by the media device to include user defined DEQ preset spectral profiles. 
     As for the case of one-dimensional control elements, for two-dimensional control elements, the parameter β in Eqn. 12—or Eqn. 18, depending on the type of DEQ processing—can be set to a fixed value of 1 for full effect or it may be controlled via an additional control interface. 
     In one embodiment, a pressure sensitive two-dimensional touch sensitive control element is used that provides a two dimensional location and a third parameter according to the pressure applied. The parameter β that determines how much of the DEQ to apply, e.g., according to Eqns. 8, 12 and 13, or Eqns. 17 and 18 depending of the type of DEQ processing, is set by a user by the pressure the user applies. 
     It should be noted that the morphing between the DEQ preset spectral profiles could also use a different, non-linear transformation such as a logarithmic transformation, than the simple ones specified in Eqns. 22 through 24. 
     Note: DEQ Control Elements Having More than Two Dimensions 
     While this disclosure provides examples of one and two-dimensional control of a DEQ system, alternate embodiments use control element having more than two dimensions, for example a virtual three-dimensional controller rendered in a computer environment or a controller that is aware of its X, Y and Z position and that can be controlled in three-dimensional space by a user. Examples of three-dimensional control elements include a gyroscopic mouse, and a gaming glove. Such and other three-dimensional control elements are known skilled in the art and may be used as the control element in different control interface embodiments of the present invention. 
     Integration of DEQ with Standard Bass and Treble Controls 
     Many media devices include standard bass and treble controls. Some embodiments of the invention have a control interface that includes control elements that control bass response and treble response analogous to standard bass and treble controls as found on many media devices, but applying a DEQ preset spectral profile EQ[b] defined by two parameters that define the amount of DEQ in a lower range and an upper range of frequency bands b. 
       FIG. 10A  show a control interface with an input control mechanism that includes a rotary bass control and a rotary treble control. Other embodiments may use slider controls. In some embodiments, these are mechanical controls included in a media device, while in other embodiments, these are virtual controls. In conventional audio equipment, such controls control the parameters of a standard bass control and treble control shelving filter. In embodiments of the present invention, the control interface is to control the amount of DEQ applied in two frequency bands—a bass band and a treble frequency band. Rather than a single DEQ control controlling in one embodiment, these are non-overlapping ranges of frequency band indices b. The bass and treble control vary two frequency dependent DEQ parameters denoted β B  and β T  that control a first lower frequency band and a second higher frequency band, the bands defined by a crossover frequency denoted B x  and a high cutoff frequency denoted B max , such that the bands for b are 0≦b&lt;B x  for the bass and B x ≦b&lt;B max  for the treble. The processing to modify the specific loudness, rather than defined by Eqns. 11 and 12 in the case of perceptual DEQ are defined by: 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     where the desired spectral shape is defined by EQ[b] as shown, for example, in  FIG. 10B , and EQ NORM [b,t] is the normalized spectral shape defined to have the same overall level as the smoothed signal loudness denoted  L   p [b,t]. 
     For the case of the DEQ processing of Eqns. 14 to 18, for the treble, processing to modify the spectral property, rather than defined by Eqns. 15 and 18 are defined by: 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     where the desired spectral shape is defined by EQ[b] as shown, for example, in  FIG. 10B , and EQ NORM [b,t] is the normalized spectral shape defined to have the same overall level as the smoothed signal spectral content denoted  L [b,t]. 
       FIG. 10A  shows the two parameters β B  and β T  annotated on the interface as percentage parameters DEQ B  and DEQ T , respectively. Thus, referring to  FIG. 10A , bass control DEQ B =0% corresponds to β B =0 and DEQ B =100% corresponds to β B =1. Similarly, treble control DEQ T =0% corresponds to β T =0 and DEQ T =100% corresponds to β T =1. 
       FIG. 10C  shows the frequency ranges for how the overall parameter β of Eqn. 18 is made up of components β B  and β T  in the bass and treble frequency band ranges that make up all frequency bands. 
     When both DEQ B  and DEQ T  are set to 0%, no alteration of the audio signal takes place. As the bass control is manipulated and the amount of DEQ B  applied is increased to 100%, spectral processing of the input audio signal according to the preset EQ[b] is carried out (only) in the lower bass frequency range for 0≦b&lt;B x . Similarly, as the treble control is manipulated and the amount of DEQ T  applied is increased to 100%, spectral processing of the input audio signal according to the preset EQ[b] is carried out (only) in the higher treble frequency range of B x ≦b&lt;B max . It should be noted that by changing the parameters DEQ B  or DEQ T  from 0% to 100%, this can introduce either a cut or boost in the audio signal depending on the characteristics of the audio signal and the desired spectral shape selected by the user. 
     Integration of DEQ with Multi-Band Equalizer Controls 
     Using frequency dependent controls to determine how a DEQ preset spectral profile is applied can be expanded beyond two frequency bands, e.g., a bass and a treble control to three separate controls. e.g., bass, mid-range and treble controls, and also to multiple frequency bands using a control interface that mimics a graphic equalizer control interface. In some embodiments, the control interface includes a plurality of control elements that each defines the amount of DEQ to apply according to a single DEQ preset spectral profile in a respective one of a corresponding plurality of contiguous frequency bands of the single DEQ preset spectral profile to provide multi-band equalizer controls. 
       FIG. 11A  shows a control interface that shows slider controls for a set of frequency bands denoted Band  1 , Band  2 , . . . , Band  5 , respectively.  FIG. 11B  shows the desired spectral shape EQ[b], while  FIG. 11C  shows how the full frequency range of b is divided into five bands defined by a set of four cross-over frequencies denoted B 1 , B 2 , B 3 , and B 4 , and a maximum frequency denoted β max . Each band control of the control interface shown in  FIG. 11A  is used to set one of a set of parameters denoted β i , i=1 . . . 5 which in the drawing are expressed as percentage quantities DEQ 1 , DEQ 2 , . . . DEQ 5 . 
     While the implementation shown in  FIGS. 11A-11C  shows multiple frequency bands Band  1 , Band  2 , . . . , Band  5  each having equal bandwidth and a consistent center frequency, in alternate embodiments, the control interface can include additional controls, such as a control for changing the respective center frequencies and bandwidths of the bands, similar to how a parametric equalizer provides such controls. 
     DEQ Processing According to Preset Device or Situation Specific Preset Spectral Profiles 
     Other aspects of the invention include applying a DEQ preset spectral profiles that are specific to a pre-defined reproduction configuration and/or reproduction environment. One feature includes selecting, e.g., automatically selecting, e.g., automatically changing the preset to a DEQ preset spectral profile according to what a device is connected. Consider for example a portable media device such as an iPod (TM of Apple Inc., Cupertino, Calif.). There can be, for example, a pre-defined DEQ preset spectral profile for when the media device is connected to (“docked to”) a home theater system, a pre-defined DEQ preset spectral profile for when the media device is connected to an automotive reproduction system, and yet another for listening to the media device output through headphones. Each reproduction situation provides a different experience and the appropriate DEQ preset spectral profile or preset profiles could be automatically selected or available for each situation. As an example, DEQ preset spectral profiles that boost very low levels of bass that are unlikely to be reproduced by smaller headphones may not be used or selected when playback is over headphones. Also a default DEQ preset spectral profile could be loaded by the system so that a consistent perceived spectral profile is provided to the user even though the reproduction method is varying. 
     An Integrated Controller for Dynamic Equalization Preset Selection and Control 
     The parameter β and a DEQ preset spectral profile EQ[b] (Eqn. 12 or Eqn. 18, depending on the type of DEQ) together provide a relatively simple manner that can be used in a media device to control the perceived spectrum of an audio signal. Furthermore, one of a plurality of pre-defined DEQ preset spectral profiles can be used, each for example applicable to a different reproduction situation or environment. One aspect of the present invention is a control interface that provides for a user a mechanism to easily select one of a set of pre-defined DEQ preset spectral profiles EQ[b] and to control the amount of DEQ being applied by controlling of the parameter β (Eqn. 12 or Eqn. 18, depending on the type of DEQ). Some versions include a mechanism to capture and store a desired spectral profile from an input audio signal. In one embodiment, the pre-defined DEQ preset spectral profiles are stored on a device. In another embodiment, universal resource locators (URLs) or pointers to the respective pre-defined DEQ preset spectral profiles are stored in the device. 
     In some embodiments, the control interface includes a display element for displaying a selection and an integrated element that provides for a control element for adjusting, e.g., adjusting the amount of DEQ to apply and a control element for indicating, e.g., for indicating a choice. As an example, in some embodiments, the control element for adjusting is a rotary control element, and the control element for indicating is by a click control element integrated with the rotary control element. 
       FIGS. 12A and 12B  show two alternate embodiments of a control interface for integrated DEQ control including selecting a DEQ preset profile and varying the amount of DEQ applied.  FIG. 12A  shows a control interface that includes an annular rotary controller  1203 , which can be an actual physical controller, or a virtual controller in the form of a display with which a user can interact. The rotary control is used as the control element for adjusting. The control interface includes a region  1205  that acts as a push button, also commonly called a click button. The click button is used as the control element for indicating. In the particular arrangement shown, the click button  1205  fills the center void region of the annular rotary controller  1203 . The control interface includes a display element  1207  configured to display actions being performed to provides a user visual feedback. 
       FIG. 12B  shows one alternative control interface in which the rotary controller and selection mechanism are combined into element  1223 : a rotary controller, e.g., a knob with integrated click control. A top view and a side view is shown in  FIG. 12B , as is the display element  1207 . 
     In some embodiments, the control interface with the integrated rotary controller and the click button ( FIG. 12A  or  FIG. 12B ) has a plurality of modes, including a selection mode in which the rotary controller is used to choose a particular pre-defined DEQ preset spectral profile of a plurality of pre-defined DEQ preset spectral profiles, and the click button is used to indicate applying the particular pre-defined DEQ preset spectral profile. 
     As one example, the modes include a control mode in which the rotary controller is used to control the amount of DEQ to apply, and the click button indicating is used to change modes. Furthermore, in some embodiments, the modes include a save mode in which the rotary controller is used to select a storage location to store a particular DEQ preset spectral profiles as one of the pre-defined spectral profiles, and the click button is used both to change modes and to save the particular DEQ preset spectral profiles as one of the pre-defined spectral profiles at the selected storage location. 
       FIG. 13  shows a simplified flow chart of how an embodiment of an integrated DEQ controller can be used for the selection, creation and storage of DEQ preset spectral profiles. 
     The flowchart in  FIG. 13  assumes that a DEQ preset spectral profile has been selected by the DEQ processing function and is actively processing the audio signal. When a preset is being applied, the user can control the amount of DEQ being applied. In the example above, it is assumed that the user control is that of the parameter β which was outlined above in  FIGS. 4A and 4B . 
     In one embodiment, the click control provides one of several actions depending on the length of depression. In an alternate embodiment, a single click and two clicks in rapid succession are used, as is common in modern computer interfaces, such as Microsoft Windows, Apple&#39;s OS X, etc. 
     While the method processes the audio signal including applying the DEQ preset spectral profile, the method continually monitors for three types of user input: a change in the rotary position, and two types of user input provided by the center click button in the embodiment of  FIG. 12A  and the rotary controller click action in the embodiment of  FIG. 12B . The two different click actions are a click action of the first kind and a click action of the second kind. 
     The monitoring is shown by blocks  1301 ,  1303 , and  1308 . While sequential monitoring is shown in  FIG. 13 , in alternate embodiments, the monitoring may be carried out by parallel monitoring, and by interrupt mechanisms, as is common skilled in the art. 
     The method includes in  1301  monitoring for change in position of the rotary controller, and in  1302 , if the position is changed, applying a new β according to the new position of the rotary controller. 
     Suppose the length of depression is used to differentiate between the click action of the first kind and the click action of the second kind, and suppose the method is configured to differentiate between a short duration click action—the click action of the first kind, and a long duration “click and hold” action—the click action of the second kind. The method includes in  1303  monitoring for a short duration click action, and in  1308  monitoring for a long duration click action. 
     In one implementation, the click action of the first kind—the short duration click action indicates the user&#39;s desire to audition and select a new DEQ preset spectral profile. This is indicated by decision block  1303  branching to Y (yes) on the right. In  1304  a DEQ preset spectral profile selection graphical user interface (GUI) is presented to the user (activated). In one embodiment, the GUI includes a multi-line display (LED or LCD) as shown in  FIGS. 12A and 12B . While the DEQ preset spectral profile selection GUI is active, the rotary controller now controls the DEQ preset spectral profile selection in the GUI instead of the parameter β of, e.g., Eqn. 12 or Eqn. 18 depending on the type of DEQ. The user selects and auditions various DEQ preset spectral profiles by rotating the rotary controller, each change causing a different DEQ preset spectral profile to be used for processing.  1305  includes detecting if there is a change in the position of the rotary controller, and if so, using the selected DEQ preset spectral profile to process the audio signal. When the listener wishes to load a currently being used profile, the user so indicated with a click action of the first kind—the short duration click action. Step  1306  monitors for the short duration click action and repeats monitoring for a change in the rotary controller until there is a short duration click action. If a short duration click action is identified by the method in  1306 , indicating the user&#39;s desire to load the currently selected preset,  1307  includes loading the selected DEQ preset spectral profile, using the loaded DEQ preset spectral profile for audio signal processing, and returning the flowchart to the start or step  1301 . 
     While the method returns to processing the audio signal, applying the DEQ preset spectral profile, the method again monitors for the three types of user input provided by the rotary controller and the click action actuator. 
     In one implementation, the click action of the second kind—the long duration click action indicates the user&#39;s desire to create a new DEQ preset spectral profile based on the spectral profile of the audio signal currently being processed and monitored. This is indicated by decision block  1308  branching to Y (yes) in the downward direction. In  1309  a DEQ preset spectral profile storage GUI is activated. In some embodiments, this takes on the simple form shown in  FIGS. 12A and 12B . In some embodiments, while the DEQ preset spectral profile storage GUI is active, the rotary controller is configured to control the DEQ preset spectral profile storage location, indicated by an index number in the GUI, instead of controlling the parameter β. In  1310  the rotary controller is monitored while the user selects a PREQ preset location. In some embodiments, while the DEQ preset spectral profile storage GUI is active, a short duration click action is used to indicate to the method the user&#39;s desire to store the DEQ spectral profile of the current audio signal being monitored in the selected DEQ preset spectral profile location.  1311  includes monitoring for a short duration click action. Such an action occurring is indicated by decision block  1311  branching to Y (yes) in the downward direction.  1312  includes storing the DEQ spectral profile of the current audio signal being monitored in the selected DEQ preset spectral profile location.  1313  includes loading and using the just stored DEQ spectral profile for audio signal processing, which then returns the process to the monitoring of processing the audio signal while monitoring for rotary or clock actions. 
     It should be noted that additional functionality is also possible, including the creation of custom preset names. This functionality may also be implemented as a virtual version of  FIGS. 4A and 4B , for example one that is rendered via touch sensitive graphical user interface such as those integrated with computers and portable media players. 
     Unless specifically stated otherwise, as apparent from the following description, it is appreciated that throughout the specification discussions utilizing terms such as “processing,” “computing,” “calculating,” “determining” or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities into other data similarly represented as physical quantities. 
     In a similar manner, the term “processor” may refer to any device or portion of a device that processes electronic data, e.g., from registers and/or memory to transform that electronic data into other electronic data that, e.g., may be stored in registers and/or memory. A “computer” or a “computing machine” or a “computing platform” may include one or more processors. 
     Note that when a method is described that includes several elements, e.g., several steps, no ordering of such elements, e.g., steps is implied, unless specifically stated. 
     In some embodiments, a computer-readable storage medium is configured with, e.g., encoded with instructions that when executed by one or more processors of a processing system such as a digital signal processing device or subsystem that includes at least one processor element and a storage subsystem, cause carrying out a method as described herein. 
     The methodologies described herein are, in some embodiments, performable by one or more processors that accept logic, instructions encoded on one or more computer-readable media. When executed by one or more of the processors, the instructions cause carrying out at least one of the methods described herein. Any processor capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken are included. Thus, one example is a typical processing system that includes one or more processors. Each processor may include one or more of a CPU or similar element, a graphics processing unit, and/or a programmable DSP unit. The processing system further may include storage subsystem that includes a memory subsystem including main RAM and/or a static RAM, and/or ROM. A bus subsystem may be included for communicating between the components. The processing system further may be a distributed processing system with processors coupled by a network, e.g., via network interface devices or wireless network interface devices. If the processing system requires a display, such a display may be included, e.g., a liquid crystal display (LCD), organic light emitting display (OLED), or a cathode ray tube (CRT) display. If manual data entry is required, the processing system also includes an input device such as one or more of an alphanumeric input unit such as a keyboard, a pointing control device such as a mouse, and so forth. The term storage device, storage subsystem, or memory unit as used herein, if clear from the context and unless explicitly stated otherwise, also encompasses a storage system such as a disk drive unit. The processing system in some configurations may include a sound output device, and a network interface device. The memory subsystem thus includes a computer-readable medium that is configured with, e.g., encoded with instructions, e.g., logic, e.g., software that when executed by one or more processors, causes carrying out one of more of the method steps described herein. The software may reside in the hard disk, or may also reside, completely or at least partially, within the RAM and/or within the processor during execution thereof by the computer system. Thus, the memory and the processor also constitute computer-readable medium on which are encoded instructions. 
     Furthermore, a computer-readable medium may form a computer program product, or be included in a computer program product. 
     In alternative embodiments, the one or more processors operate as a standalone device or may be connected, e.g., networked to other processor(s), in a networked deployment, the one or more processors may operate in the capacity of a server or a client machine in server-client network environment, or as a peer machine in a peer-to-peer or distributed network environment. The term processing system encompasses all such possibilities, unless explicitly excluded herein. The one or more processors may form a personal computer (PC), a media playback device, a tablet PC, a set-top box (STB), a Personal Digital Assistant (PDA), a cellular telephone, a Web appliance, a network router, switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. 
     Note that while some diagram(s) only show(s) a single processor and a single storage subsystem, e.g., a single memory that stores the logic including instructions, those skilled in the art will understand that many of the components described above are included, but not explicitly shown or described in order not to obscure the inventive aspect. For example, while only a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. 
     Thus, one embodiment of each of the methods described herein is in the form of a computer-readable medium configured with a set of instructions, e.g., a computer program that when executed on one or more processors, e.g., one or more processors that are part of a media device, cause carrying out of method steps. Thus, as will be appreciated by those skilled in the art, embodiments of the present invention may be embodied as a method, an apparatus such as a special purpose apparatus, an apparatus such as a data processing system, or a computer-readable storage medium, e.g., as a computer program product. The computer-readable medium is configured with a set of instructions that when executed by one or more processors cause carrying out method steps. Accordingly, aspects of the present invention may take the form of a method, an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of computer readable medium, e.g., a computer program product as a computer-readable storage medium with computer-readable program code embodied in the medium. 
     While the computer readable medium is shown in an example embodiment to be a single medium, the term “computer readable medium” should be taken to include a single medium or multiple media, e.g., a centralized storage device for a centralized database, or distributed storage for a distributed database, and/or associated caches and servers that store the one or more sets of instructions. The term “computer readable medium” shall also be taken to include any tangible storage medium that is capable of storing or encoding instructions for execution by one or more of the processors and that cause the one or more processors to perform method steps of any one or more of the methodologies of the present invention. A computer readable medium may take many forms, including but not limited to, non-volatile media and/or volatile media. Non-volatile media includes, for example, optical storage, magnetic disks, and/or magneto-optical disks. Volatile media includes dynamic memory, such as main memory. For example, the term “computer readable medium” shall accordingly be taken to be included, but not be limited to, in one set of embodiment, a tangible computer-readable medium, e.g., a solid-state memory, or a computer software product encoded in computer-readable optical or magnetic media. 
     It will be understood that the steps of methods discussed are performed in one embodiment by an appropriate processor (or processors) of a processing (i.e., computer) system executing instructions stored in storage. It will also be understood that embodiments of the present invention are not limited to any particular implementation or programming technique and that the invention may be implemented using any appropriate techniques for implementing the functionality described herein. Furthermore, embodiments are not limited to any particular programming language or operating system. 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill skilled in the art from this disclosure, in one or more embodiments. 
     Similarly it should be appreciated that in the above description of example embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the DESCRIPTION OF EXAMPLE EMBODIMENTS are hereby expressly incorporated into this DESCRIPTION OF EXAMPLE EMBODIMENTS, with each claim standing on its own as a separate embodiment of this invention. 
     Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination. 
     Furthermore, some of the embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a computer system or by other means of carrying out the function. Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus embodiment is an example of a means for carrying out the function performed by the element for the purpose of carrying out the invention. 
     In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description. 
     As used herein, unless otherwise specified, the use of the ordinal adjectives “first”, “second”, “third”, etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner. 
     All U.S. patents, U.S. patent applications, and International (PCT) patent applications designating the United States cited herein are hereby incorporated by reference. In the case the Patent Rules or Statutes do not permit incorporation by reference of material that itself incorporates information by reference, the incorporation by reference of the material herein excludes any information incorporated by reference in such incorporated by reference material, unless such information is explicitly incorporated herein by reference. 
     In the claims below and the description herein, any one of the terms comprising, comprised of or which comprises is an open term that means including at least the elements/features that follow, but not excluding others. Thus, the term comprising, when used in the claims, should not be interpreted as being limitative to the means or elements or steps listed thereafter. For example, the scope of the expression a device comprising A and B should not be limited to devices consisting of only elements A and B. Any one of the terms including or which includes or that includes as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, including is synonymous with and means comprising. 
     Similarly, it is to be noticed that the term coupled, when used in the claims, should not be interpreted as being limitative to direct connections only. The terms “coupled” and “connected,” along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression a device A coupled to a device B should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. “Coupled” may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other. 
     Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the scope of the invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.