Power mitigation for loudspeaker amplifiers

A power mitigation algorithm in a loudspeaker amplification system that includes a loudspeaker driver, an audio amplifier, and a constant output power, power supply. A power requirement for the amplifier to output an audio signal is determined. A gain adjustment signal is then determined based on a difference between the power requirement and a power budget of the amplifier. Gain of the audio signal is adjusted according to the gain adjustment signal, for output through the loudspeaker driver. As a result, a peak level of the power consumption of the amplifier while outputting the gain-adjusted audio signal becomes less than the power budget. Other embodiments are also described and claimed.

FIELD

An aspect of the disclosure relates to a digital processor performing a power mitigation algorithm upon an audio signal that is being output by a loudspeaker driver, to detect the power requirements that exceed a power budget of an audio amplifier that is driving the loudspeaker driver with the audio signal. Other aspects are also described.

BACKGROUND

A regulated power supply is an electronic component that supplies electrical energy to an electrical load. Normally, most power supplies regulate either their output voltage or output current to remain at a preset, constant level, despite variations in the load.

In the case of a typical audio amplification system, an audio amplifier uses the electrical energy from a voltage regulated DC power supply to amplify an audio signal to drive a loudspeaker driver, where the amplifier and the driver are together acting as the load. If, however, the electrical power required by the audio amplifier to amplify the audio signal exceeds the power available from the power supply, performance by the loudspeaker driver may suffer. For example, when the amplifier attempts to overdraw the power supply during a peak excursion of an audio signal, such as a large bass hit, the regulated DC voltage drops thereby causing loudspeaker performance to suffer. A local energy storage device such as a capacitor may be added to the output of the power supply, to assist with meeting such peak power demands.

SUMMARY

Systems, methods, and articles of manufacture are provided for a digital processor that performs a power mitigation algorithm upon an audio signal that is being output by a loudspeaker driver, where the processor detects the power requirements that exceed a power budget of an audio amplifier that is driving the loudspeaker driver with the audio signal.

An aspect of the disclosure is a loudspeaker amplification system that mitigates its peak power requirements during playback of audio content, to stay within a “power budget” and as a result avoids overloading its constant output power, power supply. This enables the constant output power rating to be substantially less than the peak power levels expected of its load, and the power supply circuit can therefore be made physically smaller while still being able to output content such as music that exhibits relatively high power peaks as compared to the average power level, at an acceptable quality. The power budget may be defined as the amount of power that is available for the audio amplifier to drive its loudspeaker driver to output the audio content. Specifically, the power budget may be the difference between a constant output power rating of the power supply and the total power required by all elements within the system that are part of the load except for the particular audio amplifier that is excepted to exhibit high power peaks during playback. For example, the load may include a system logic board, light emitting diodes (LEDs) or a display screen, several audio amplifiers such as tweeter amplifiers that do not exhibit the high power peaks that are of concern, in addition to at least one audio amplifier such as a woofer amplifier that is expected to have high power peak demands.

One aspect of the disclosure is a method for performing a power mitigation algorithm that avoids overdrawing power from a constant output power, power supply. This process is also referred to here as a dynamic peak power mitigation process. The method may be performed by a digital signal processor, which receives a digital audio signal that is to drive a loudspeaker transducer or driver (e.g., a woofer). The processor calculates power needed by an audio amplifier (power requirement) while driving the woofer to output the audio signal during a given time interval or window. Specifically, the determined power requirement is that which the audio amplifier is expected to draw from the power supply, in order to amplify the audio signal during the given time interval or window. This power may exceed the constant output power rating of the power supply. Accordingly, a gain adjustment signal is determined that is based on or includes a difference between the determined power requirement and a power budget of the audio amplifier. Using the gain adjustment signal, gain (magnitude or amplitude) of the audio signal is then adjusted to produce a gain-adjusted audio signal. Since the gain adjustment is based on the available power from the power supply (according to the power budget), the audio amplifier amplifies the adjusted audio signal without overdrawing the power supply. Any peaks in the audio signal that would have resulted in exceeding the power budget (also referred to here as high power peaks) are thus automatically reduced in the gain-adjusted audio signal (which is outputted through the loudspeaker driver.)

In one aspect, the gain adjustment signal is determined based on “moving” averages of instantaneous power (needed for the woofer to output the audio signal), determined over several moving or sliding time intervals or windows, of different sizes. Several average instantaneous power requirements are computed, each average being an average of the instantaneous power requirement values computed in a respective window. For each of the windows, a difference between the average in that window and the power budget is computed. The gain adjustment signal is then determined, according to the largest difference. In other words, the resulting gain adjustment that is applied to the audio signal may be in proportion to the largest difference, and not any other differences computed for other windows. The gain adjustment signal may for example be in the range of 0 dB to some maximum attenuation value that is available (e.g., a most negative dB value.) The system thus attenuates the audio signal as needed to ensure that the power drawn by the audio amplifier stays within its power budget. The above process to update the gain adjustment signal then repeats, for a new window position (the windows slide or move to another time interval of the audio signal, hence the reference here to “moving averages”.)

In one aspect, instead of having a single or fixed power budget for all of the different-sized windows, a separate power budget is determined for each window.

In another aspect, the power budget that is used to determine the gain adjustment signal for a woofer input signal may be smaller due to the power that is drawn by additional audio amplifiers (driving additional loudspeakers), from the same constant output power, power supply. The additional loudspeakers may be higher frequency loudspeakers, e.g., tweeters, as opposed to a lower frequency loudspeaker referred to here as a woofer. In this aspect, the system calculates an instantaneous power requirement (e.g., one sample) for each of several, tweeter audio signals, and combines (e.g., sums or adds) these calculated instantaneous power requirements, for all of the tweeters, into a single, total power requirement. Finally, the power budget for the woofer is computed as a difference between 1) the constant output power rating of the power supply and 2) the total power requirement for driving the tweeters.

In one aspect, the system calculates the total power requirement for the tweeter amplifiers as follows. For each window (of several samples of the tweeter signals), several instantaneous, total power requirement values (one for each sample within a given window) are computed. These instantaneous, total power requirement values are then averaged, resulting in a single, average total power requirement for each window (average power required to drive all of the additional loudspeakers to output the tweeter audio signals, in the given window.) Note that each window may be different (covers a different time interval, of the tweeter audio signals) but all of the windows may overlap each other.

Another aspect of the disclosure is a time domain-based digital signal processing technique, which calculates the instantaneous power requirement for an audio amplifier that is driving a loudspeaker driver, e.g., a woofer. A loudspeaker driver admittance filter is defined, as a digital filter, which represents the input admittance of the loudspeaker driver. The filter is applied to transform an audio driver input signal that is in voltage domain (as a discrete-time sequence of driver input voltage samples, or instantaneous voltage values) into an audio driver instantaneous current, and the latter is multiplied by the audio driver input signal (in voltage domain) to obtain instantaneous, driver input power values (pursuant to the relation power=voltage*current.)

DETAILED DESCRIPTION

Several aspects of the invention with reference to the appended drawings are now explained. Whenever the shapes, relative positions and other aspects of the parts described in the aspects are not explicitly defined, the scope of the invention is not limited only to the parts shown, which are meant merely for the purpose of illustration. Also, while numerous details are set forth, it is understood that some aspects of the invention may be practiced without these details. In other instances, well-known circuits, structures, and techniques have not been shown in detail so as not to obscure the understanding of this description.

Some conventional audio amplifier designs require that the power supply output power rating be at least as high as the peak power demands of the audio content (e.g., music) that is expected to be played through the loudspeakers. This means that the power supply is effectively “over designed”, to have a rating equal to or greater than the peak power levels that may be drawn by the load during for example music playback. Such over-designed power supply circuits tend to be quite large (e.g., because larger components, such as electrolytic capacitors are required.) Smaller and more compact loudspeaker amplification systems (e.g., consumer electronics, smart or intelligent speakers) cannot take advantage of such an easy solution, because of their limited internal space.

FIG. 1shows a loudspeaker amplification system100that includes a generally cylindrical shaped loudspeaker cabinet110that has integrated therein a loudspeaker array120with individual loudspeaker drivers125(or loudspeaker transducers) that are arranged side by side and circumferentially around a center vertical axis of the cabinet110. The cabinet110also has integrated therein a separate loudspeaker driver115that is positioned at a top of the loudspeaker cabinet110. In other aspects, however, the separate loudspeaker driver115may be positioned at other locations (e.g., at the bottom or at the side of the cabinet110.) In one aspect, as will be later described, functions, such as digital signal processing and in particular a power mitigation algorithm, may be performed by circuit components (or elements) within the loudspeaker cabinet110. In another aspect, these functions may be performed by electronic components outside the loudspeaker cabinet110, such as a separate audio receiver, not shown, that produces the loudspeaker driver input signals in digital form which are then wirelessly transmitted to the loudspeaker cabinet. The loudspeaker cabinet may communicate, via either wired or wireless means, with the audio receiver. In the example shown, however, a portion or all of the electronic hardware components, sometimes found within an audio receiver (e.g., a rendering processor), are integrated in the enclosure of the loudspeaker cabinet110. In one aspect, the loudspeaker cabinet110may be part of a home audio system or an audio system in a vehicle.

The loudspeaker drivers125,115may be electrodynamic drivers, and may include some that are specifically designed for outputting sound (or their output response is greatest at) certain, different frequency bands. For example, driver115may be designed to operate better, more efficiently, or with greatest response in a low frequency band that is lower than the operating frequency range of certain other drivers. Such low frequency drivers may be generically referred to here as woofers. There may also be drivers125included within the loudspeaker array120that are designed to operate better or more efficiently or have greatest response in a high frequency band (that is higher than the operating frequency range of certain other drivers, and higher than the low frequency band) and may be generically referred to here as tweeters. In one aspect, the drivers125may be “full-range” loudspeaker drivers that reproduce as much of the audible frequency range as possible given the physical volume (physical space) constraints on the driver, except perhaps for very low frequencies, e.g., below 100 Hz. The loudspeaker drivers125are driven with full-range audio driver signals that may also contain audio in the low frequency band that is preferred by the driver115.

FIG. 2shows a block diagram of the loudspeaker amplification system100including the loudspeaker cabinet110, an input audio source225, and an AC mains input201. The loudspeaker cabinet110in this aspect also includes a system logic board202with a rendering processor205, a power supply220, storage capacitors240, digital to analog converters (DAC)230and231, low range audio power amplifiers235and full range audio power amplifiers236. The term “low range” may refer to a frequency range that is typically preferred by a woofer. The term “full range” may refer to an audio frequency range that is wider than the low frequency range and such as one that is typically preferred by a midrange or tweeter. Note however that the concepts described here are not limited to the combination of a low range audio amplification and output path and a full range audio amplification and output path, as instead they may be applied to for example a system having a single audio amplification and output path, e.g., a single low range path, or to a system having both a low range path and high range path where the term “high range” in that case may refer to an audio frequency band that is above the low range.

As described in connection withFIG. 1, the loudspeaker cabinet in this aspect also includes the array120of additional loudspeaker drivers125, along with the separate loudspeaker driver115. In this example, the amplifier235has an output coupled to drive a signal input of loudspeaker driver115; and each of the full range audio power amplifiers236has an output coupled to drive a signal input of a respective loudspeaker driver125. Each amplifier235and236receives an analog input from a respective digital to analog converter (DAC) (e.g., amplifier235receives its analog input from DAC230, while each amplifier236receives an analog input from a respective DAC231), where each DAC230and231receives a separate, input digital audio signal through a communications link245. Although the DACs230and231and the amplifiers235and236are shown as separate blocks, in one aspect the electronic circuit components for these may be combined for one or more drivers, in order to provide for a more efficient digital to analog conversion and amplification operation of the individual driver signals, e.g., using for example class D amplifier technologies.

The system logic board202may be the loudspeaker cabinet's main circuit board that includes the rendering processor205that may perform several different computational processes, as later described. Although shown in this figure to only include the rendering processor, in one aspect, the system logic board202may also include at least some other electronic components e.g., such as the DACs230and231, audio amplifiers235,236. In another aspect, the system logic board202may also include electronic components not shown in this figure (e.g., logic circuits, memory), and/or interface with components external to the board202, e.g., light emitting diodes (LEDs) and a display screen.

The individual digital audio driver signal for each of the drivers125,115is delivered through the audio communication link245, from a rendering processor205. In this case, since the rendering processor205is implemented on the system logic board202, within the loudspeaker cabinet110, the audio communication link245is a wired connection such as any combination of on-chip and chip-to-chip or electro-optical interconnects. If however the rendering processor205is implemented within a separate enclosure from the loudspeaker cabinet110(e.g., as part of an audio receiver as previously described inFIG. 1), the audio communication link245is more likely to be a wireless digital communication link, such as a BLUETOOTH link or a wireless local area network link. In other instances however, the audio communication link245may be over a physical cable, such as a digital optical audio cable (e.g., a TOSLINK connection), or a high-definition multi-media interface (HDMI) cable.

In one aspect, the power supply220is configured to provide a constant output power to its load. For example, the power supply220may have a constant output power rating of 100 Watts. This means that the power supply220automatically regulates its output voltage V at a maximum value and with a certain current limit, but when the output current I (the load) exceeds the current limit, the output voltage droops. However, the power supply220will respond to this voltage droop by entering a power-limited mode in which it increases its current limit as it detects that its output voltage is dropping such that its output power V*I stays constant, at 100 Watts in this example. Thus, while the audio amplifiers235,236are driving their respective loudspeaker drivers to output audio content, such as music, there are instances of elevated sound pressure levels that cause the power supply220to enter into this power-limited mode. This is in contrast to a regulated output voltage DC power supply that maintains a constant output voltage, despite changes in its output current.

Storage capacitors240are energy reservoirs, designed for supplying the load with bursts of energy, for short amounts of time. These bursts of energy provide the elements that make up the power supply load with more power than can be provided by the power supply220itself. In other words, the power supply is assisted by the storage capacitors240that are at the output of the power supply220. For example, a music signal may have a crest factor of at least four (4), or a peak-to-average power ratio of at least sixteen (16). In one aspect, a “peak” in an audio signal, as the term is used here, may be defined as that portion (e.g., sample) of the audio signal that results in an amplifier power consumption level (during its playback) that is at least twice the average power amplifier level during playback of the entire audio program. During periods in which high peak power is required by the load, the storage capacitors240, which have little internal resistance can discharge their stored energy quickly, thereby providing the load (audio amplifier) with sufficient power to output the audio signal at the peak power level. For example, energy stored in a capacitor may be written as:

Energy=12⁢CV2
where C is the capacitance of the capacitor, and V is the voltage across the capacitor. The amount of energy discharged by the capacitor is thus proportional to the square of a decrease in voltage across the capacitor, or in other words,

Discharged⁢⁢Energy=12⁢C⁡(Vi2-Vf2)
where Vi is a previous voltage outputted by the power supply and Vf is a current voltage being outputted by the power supply. Thus, continuing with the previous example, during the times in which the audio amplifier235requires additional power to amplify an audio signal (e.g., because a portion of the audio signal has a large amplitude due to for example a bass drum hit), the storage capacitors240may be relied upon to provide this additional power; the power supply then responds by charging the storage capacitors back up to the previous voltage, at its constant output power level.

In one aspect, since the characteristics of the power supply220and the storage capacitors240are known, the system is capable of determining a power budget for certain electronic elements within the system during certain modes of operation, as described above. A power budget may be defined as an available amount of power that the power supply220may provide to one or more of its load elements, under operational conditions. In the case of the loudspeaker amplification system100, the power budget may be the amount of power available for the audio amplifier235to drive the loudspeaker driver115, to output an audio signal. In one aspect, this “available” power may be the difference between i) the constant output power rating of the power supply and ii) the total power required (or expected to be drawn by) all load elements within the system, other than the audio amplifier235. For example, the load elements may include the system logical board, LEDs and/or a display screen, and audio amplifiers such as full range audio power amplifiers236that do not normally exhibit high power peaks, in addition to the low range audio power amplifier235that is expected to have high peak power demands. Knowing a power budget for the audio amplifier235allows the system to adjust that element's functionality in order to ensure that the element does not draw more power than is currently available. More about power budgets is described below in connection withFIGS. 3-5.

Managing the power requirements of elements within the system100based on a power budget as described here may provide several advantages. For instance, this ensures that the power supply220and/or storage capacitors240are not being overdrawn by the system's elements. Furthermore, unlike other systems that would require a bulky, over-designed, regulated DC voltage power supply to actually produce the peak power requirements, which take up a significant amount of internal space, the loudspeaker amplification system100is able to accommodate such requirements with a more compact, constant output power rating, power supply220, in combination with the storage capacitors240. Thus, the loudspeaker amplification system100can provide enough power to satisfy the requirements of system elements, with a smaller sized power supply220(and capacitors240) that fit within the loudspeaker cabinet110, e.g., one having a diameter of less than six inches and a height of less than seven inches.

Continuing withFIG. 2, the system100has a rendering processor205that is receiving one or more input audio channels or audio signals, of a piece of sound program content from an input audio source225. The input audio source225may provide a digital input (audio signal) or an analog input (audio signal.) The input audio source225may include a programmed processor that is running a media player application program and may include a decoder that is producing digital audio for the rendering processor205, e.g., in a stereo left and right, in a 5.1-surround format, or other available format. The decoder may be capable of decoding an encoded audio signal, which has been encoded using any suitable audio codec, e.g., Advanced Audio Coding (AAC), MPEG Audio Layer II, MPEG Audio Layer III, and Free Lossless Audio Codec (FLAC). Alternatively, the input audio source may include a codec that is converting an analog or optical audio signal, from a line input, for example, into digital form for the rendering processor.

In one aspect, the rendering processor205includes an audio signal processing block210and a peak power mitigation block215. The audio signal processing block210may modify (or adjust) the digital audio signals received from the input audio source225for instance to perform spectral shaping or dynamic range control, create a downmix from multiple channels in the audio signal, adjust gain of an audio signal according to a user-set volume level, or other digital signal processing, to produce one or more loudspeaker driver signals. In one aspect, the processing block may include a beamformer that is configured to produce individual loudspeaker driver input signals for the drivers125so as to “render” the audio content of the input audio as multiple, simultaneous desired beams emitted by the drivers125, operating as a beamforming loudspeaker array.

The peak power mitigation block215is to receive a processed audio signal (loudspeaker driver input signal, also referred to as an audio driver signal, or simply audio signal) from the audio signal processing block210, and adjusts the gain of that signal as needed to mitigate the peak power requirements of the audio content within the audio signal. The gain-adjusted audio signal (gain adjusted loudspeaker driver input signal) will thus stay within the power budget (as defined above) that is associated with the audio amplifier that will be driving that signal. Any peaks in the audio signal that would result in exceeding the power budget are reduced automatically, by the peak power mitigation block215. To do so, the power mitigation block215determines a gain adjustment signal based on a difference between i) a power requirement for the audio amplifier235to amplify the audio driver signal with which it drives the loudspeaker driver115and ii) a power budget of the audio amplifier235. Once determined, the gain adjustment signal is applied to the audio driver signal to produce a gain-adjusted (e.g., attenuated) audio driver signal, such that when the audio amplifier235amplifies the gain-adjusted audio driver signal, power drawn by the audio amplifier does not exceed the power budget. More about how the peak power mitigation block215mitigates peak power requirements is described inFIGS. 3-5. In one aspect, since the operations performed by the block215relate to power, which may be non-linear, at least some of those operations are performed in the time domain, rather than in the frequency domain. In another aspect, at least some of the operations are performed in the frequency domain. In another aspect, at least some of the operations, such as linear operations, may be performed upstream of the audio signal processing block210. In another aspect, the operations performed in the block215are the last or most downstream operations that are performed upon the audio driver signals before the latter are received by the DAC230(and/or DACs231), through the communication link245.

Note that the term “difference” as used in this document may refer to a comparison that can be ascertained by computing i) a ratio between the two values (e.g., average power in a window divided by the power budget, for example in linear units), or ii) a subtraction between the two values (e.g., average power in a window minus the power budget, for example in units of dB.) Thus, in some cases, a division symbol and a subtraction symbol (such as a summing junction with one of the inputs having a negative sign in front) in the drawings are both examples of computing a difference. In other cases, a division symbol may represent multiplication by a scaling factor. Note also that a format conversion may need to be performed upon a value, before a given operation, but are not shown in the drawings, e.g., conversion between linear units and dB units.

FIG. 3shows a flow diagram of one aspect of a process300of the peak power mitigation algorithm that mitigates peak power requirements of an audio driver signal. The process300may be performed by the peak power mitigation block215. Specifically, this figure shows a low-range driver path311that mitigates peak power requirements of a low frequency range or low range driver signal301, in order to stay within a power budget (e.g., a first power budget.) Also, there is an optional, full-range driver path312that mitigates peak power requirements for amplifying several (here, seven, as an example) full frequency range or full range driver signals302, in order for the full range audio amplifiers236to stay within a different (e.g., second) power budget. In one aspect, the low-range driver signal301is a signal that has primarily low frequency band audio and not high frequency band audio, while the full-range driver signals302are signals that have primarily high frequency band audio, which is higher in frequency than the low frequency band audio of the low-range driver signal301. In other words, the use of the term “full range” or “full frequency range” in connection with the driver signals302does not mean that there is audio that fills the entire audio band.

For each path311,312, there is a window of the respective driver signal301,302that is processed as described below to result in a gain adjustment signal that may then be applied to somewhere within that window, at the multiplier block (as shown for each path.) The windows are then moved or slide forward in time (by a certain amount), and the blocks in each path are repeated upon the newly moved windows to result in an update to the gain adjustment signal, and the updated gain adjustment signal is then applied to a newly moved window (at the multiplier block for each path.)

In blocks305and310of the low-range driver path311, the mitigation block determines (e.g., calculates or estimates) the power requirement needed to supply the audio amplifier235that is driving the loudspeaker driver115to output the low-range audio driver signal301. This may encompass first determining the amount of power that is expected to be drawn (from the power supply220) by the audio amplifier235to output a portion, e.g., one sample, of the low-range audio driver signal301through the loudspeaker driver115. This is also referred to here as an instantaneous power requirement and is done for several portions (samples) in a window or time interval, and for multiple windows (block305). The multiple windows or time intervals may be said to be overlapping, or overlap each other in time, as explained below using the example inFIG. 4.

The mitigation block next determines an average of the calculated instantaneous power requirements over each window (at block310). In one aspect, the several windows may be overlapping, e.g., at least partially overlap each other in time, thereby having at least one instantaneous power requirement in common between at least two windows. Each window represents a different time interval of the audio driver signal.FIG. 4shows a graph400that illustrates an example of the determined, instantaneous power requirements405which are to be averaged over several, overlapping windows of different sizes, Tavg/2, Tavg/4, and Tavg/8, each encompassing a different amount of time but all being subsets of a largest window Tavg. The window Tavg is the longest in time of the windows and contains 31 samples; the window Tavg/2 is half as long as the window Tavg and so contains 16 samples; the window Tavg/4 is a quarter of the length of window Tavg; and the window Tavg/8 is an eighth of the length of Tavg. The mitigation block determines the average power for window Tavg/8, by averaging in this example only three instantaneous power requirement values410that are within that window. Note that these particular four windows are just examples—the actual number of windows and/or their sizes (number of samples in them) may vary.

Note that the term “average” as used in this document with reference to calculating a power requirement in a window or time interval is used generically, as referring to any suitable measure of central tendency.

Some of the operations described above that are performed in the low range driver signal path311to compute a power requirement are repeated by the mitigation block215in the full-range driver signal path312. For example, in block315, the mitigation block215determines (e.g., calculates or estimates), for at least a portion (e.g., a sample, or an audio frame) of each of the full-range audio driver signals302, the instantaneous power requirement needed to supply a respective loudspeaker driver125to output the full-range driver signal during a given time interval. This is similar to the operations described above for block305. Then, in block320, the mitigation block215determines an average of the calculated instantaneous power requirements (for the full-range driver signals302) in each of the same windows, as described in block310, and for example as shown inFIG. 4.

In one aspect, since there are several full-range driver signals302, the determination of their power requirement in block315may be different than in block305for the single, low-range driver signal301. For instance, the mitigation block215may calculate an instantaneous power requirement for each of the full-range driver signals302and, as there are several full-range driver signals302, it then combines the calculated instantaneous power requirements into a single, instantaneous total power requirement. This is repeated for several portions (samples) in a window, and for the multiple windows, before determining an average of those instantaneous total power requirements for each window (in block320.) For example, referring toFIG. 4, when determining the average power for the full-range driver signals302over the window Tavg/8, each of the spikes that are shown inFIG. 4within the window Tavg/8 is actually a power value that is a combination (e.g., sum) of the instantaneous power requirements of the several full-range audio driver signals302.

At block325the mitigation block215determines, for each window, a corresponding, first power budget that is to be used in the low range path311. In one aspect, the system determines the first power budget (for each window) as a difference between a constant output power rating of the power supply220and the amount of power expected to be drawn by the system elements (in that window) other than the low range audio power amplifier235. For example, a first power budget for window Tavg may be the difference between the constant output power rating and the determined average of the instantaneous total power requirements in the window Tavg, which each of the instantaneous total power requirements is the sum of the power requirements of all of the full-range audio driver signals302(at a given sample.) In other words, it is an amount of available power left from the power supply220after deducting the power requirements of the full range audio amplifiers236that output the full-range driver signals302. In one aspect, the first power budget may also take into account or reflect a further reduction, due to the power requirements of other elements within the system that complete the load on the power supply (e.g., the logic board202, LEDs, and/or a display screen).

Next, in block330the mitigation block215determines for each window a difference between i) the average power in the window as determined at block310and ii) the window's corresponding first power budget as determined in block325. In the example ofFIG. 4, four such differences are computed that correspond to the four windows Tavg, Tavg/2, Tavg/4 and Tavg/8, respectively.

Next, in block335, the mitigation block215determines (e.g., chooses) a first gain adjustment signal, according to the largest one of the four differences (largest determined difference.) The low-range driver signal301is then multiplied by the gain adjustment signal, producing a gain-adjusted (e.g., mitigated) driver audio signal. Specifically, the magnitude or gain in a particular time interval of the driver signal is adjusted according to the gain adjustment signal to produce the gain-adjusted audio signal, and therefore, any peaks in that particular time interval of the low range driver signal301that would have resulted in exceeding the power budget are thus automatically reduced in the gain-adjusted driver audio signal, which is then outputted through the loudspeaker driver115. In one aspect, by selecting the largest difference from amongst the four windows and applying the resulting gain adjustment signal to all of the windows, the algorithm ensures that the low range audio amplifier stays within its power budget during all of the windows.

In one aspect, the gain adjustment signal is multiplied by the low range driver signal301in the time domain. Once multiplied, the gain-adjusted driver signal is then directly outputted to the power amplifier235through the loudspeaker driver115, thus, making the mitigation algorithm and gain adjustment performed on the low range driver signal301the last digital signal processing operation prior to being output through the loudspeaker driver115. In one aspect, the gain adjustment signal is multiplied only with a portion of the low range driver signal301that corresponds to the window that resulted in the largest difference between average power and the first power budget. For example, if the window Tavg8 produced the largest difference, then only window Tavg is multiplied by the gain adjustment signal. In another aspect, the largest window of which all others are subset, e.g., Tavg in the example here, is multiplied by the gain adjustment signal.

Returning to the full-range driver path312, in blocks340,345the mitigation block may perform similar operations as those described in above for blocks330,335. For example, in block340, the mitigation block215determines for each window a difference between i) the average power needed to output all of the full-range driver signals302in that window and ii) a corresponding, second power budget available during that window. Unlike the first power budget, which takes into account the average power required to output all of the full-range driver signals302and which may vary per moving window, the second power budget may be a predetermined and fixed amount of power that is “reserved” for the full-range audio power amplifiers236. Next, in block345, the mitigation block215determines a second gain adjustment signal, according to the largest of determined differences from block340. The second gain adjustment signal may then be multiplied by a selected window of each of the full-range driver signals302, to adjust gain of each of the driver signals. Each gain-adjusted driver signal is then sent to its respective audio amplifier236to drive a respective loudspeaker driver125(seeFIG. 2.)

In one aspect, the second gain adjustment signal is applied unchanged to each full-range driver signal302, but only to the range of frequencies that are actually used to drive the respective loudspeaker driver125. In another aspect, the gain adjustment signal may be applied differently (e.g., a selected frequency range vs. or all available frequency ranges) to selected ones of the full-range driver signals302, based on the effectiveness of each driver signals' respective loudspeaker driver125.

In one aspect, the second gain adjustment signal is multiplied only by the window that resulted in the largest difference between average power and the second power budget of the full-range driver signals that corresponds to the same time period of the largest window. In one aspect, the second gain adjustment signal is multiplied only with a portion of the full range driver signals302that corresponds to the window that resulted in the largest difference between average power and the second power budget. For example, if the window Tavg8 produced the largest difference, then only window Tavg is multiplied by the second gain adjustment signal. In another aspect, the largest window of which all others are subset, e.g., Tavg in the example here, is multiplied by the second gain adjustment signal.

FIG. 5shows an example of the peak power mitigation algorithm ofFIG. 3having the low-range driver path311and the full-range driver path312. In one aspect, the low-range audio driver signal301that is received at the multiplier block505may have been decimated (or downsampled) to reduce the sampling rate of the signal, for purposes of complexity reduction. Starting with block505of the low range driver path311, each sample of the decimated signal is multiplied by a known, pre-determined gain, AmpGain, of the audio amplifier235to produce a “gain increased” magnitude of the decimated signal, which is an example of an audio driver input signal in the voltage domain, or simply an audio driver input voltage signal. In other words, the result of this multiplication operation is the (estimated) output voltage of the audio amplifier235, if it were to amplify the portion of the decimated signal for output by the loudspeaker driver115. Next, an admittance filter510receives the gain increased magnitude samples (representing voltage, V, samples) to produce current I samples (also referred to here as the audio driver instantaneous current signal, or a “current response”, representing the input current of the loudspeaker driver115.) A finite impulse response filter may be used as the admittance filter510to model the loudspeaker driver115. To more accurately model the loudspeaker driver115, the admittance filter510is configured by selecting its filter coefficients from those that have been stored in a lookup table in memory, based on a back volume temperature reading of the loudspeaker driver115(not shown.) The resulting current response also represents the current drawn from the power supply to drive the loudspeaker driver115to output the portion of the decimated signal.

At block511, the current response from the admittance filter510is then multiplied by the output voltage from block505. Since Power=Current*Voltage, the result of this multiplication is the instantaneous power requirement that is needed to drive the loudspeaker driver115to output that portion (sample) of the audio signal. This power value, however, may not be an accurate value, since it does not take into account other variables (e.g., the efficiency of the audio amplifier235.) Thus, the instantaneous power requirement is divided by a pre-defined amplifier efficiency value, AmpEff (at block515). In addition, to account for quiescent power required by the audio amplifier235to perform its operations, a power quiescent power value, Quie Pwr, is added to the efficiency-adjusted instantaneous power (at block520). The result is a more accurate estimate of the instantaneous power requirement that is needed by the audio amplifier235to drive the loudspeaker driver115to output this portion of the audio signal, as an example of the more general description given above in connection with block305ofFIG. 3.

Staying withFIG. 5, the mitigation algorithm provides several calculated instantaneous power requirements that cover the predefined windows or time intervals, e.g., the four windows Tavg, Tavg/2, Tavg/4, and Tavg/8, of the low-range audio driver signal301in several parallel processing paths, each corresponding to a respective, different sized window (e.g., Tavg, Tavg/2, Tavg/4, and Tavg/8). For each of the paths, an average of the calculated instantaneous power requirements over its respective window is determined (blocks525), as also described more generally in connection withFIG. 3andFIG. 4above. Next, at blocks530, the algorithm determines a difference between the average power over each window and a first power budget that corresponds to the window, as described in block330ofFIG. 3. More about how the first power budgets are determined from the full range path312is also described later. In this example, the determined difference is a ratio (e.g., a division) between the average power and its respective first power budget value, but could alternatively be a subtraction (e.g., in dB domain.) In one aspect, the square root of each of these differences may then be taken (not shown inFIG. 5) to return to voltage domain, since power normally changes as a square of the voltage applied on an electrical load (e.g., a loudspeaker driver.) At blocks535, the algorithm clips or limits each of the differences (after the square root operation) to be no higher than 0 dB, consistent with a power mitigation algorithm that either allows the audio signal to pass through unchanged (0 dB gain adjustment) or attenuates (a negative dB gain adjustment). In other words, the mitigation algorithm does not boost the audio signal, when the average power is less than the first power budget.

Next, in block540, the gain adjustment signal is determined, according to the largest difference, as also described above in connection with block335ofFIG. 3. Here, the least negative dB value, of the four dB values that are provided by the block535, is selected to be the gain adjustment signal. This signal is then multiplied (block545) by a selected window of the low-range driver signal301, and then sent to the audio amplifier235for driving loudspeaker driver115. Thus, the system applies the gain adjustment signal, which is being updated sequentially for each portion or window of the low range driver signal301, to that portion or window of the driver signal301, thereby ensuring that the audio amplifier235does not overdraw power from the power supply, while driving the loudspeaker driver115to output the audio signal.

In one aspect, the gain adjustment signal is multiplied only by the portion of the low-range driver signal301that corresponds with the window having the largest difference (from which the gain adjustment signal was determined.) For example, if the algorithm determines the gain adjustment signal from the difference associated with window Tavg/2 (the difference between the average power and the first power budget over window Tavg/2 was the largest of the four windows), then only the portion of the low-range driver signal301that extends over window Tavg/2 is multiplied by the gain adjustment signal.

In one aspect, the gain adjustment signal may be modified before being multiplied by the driver signal301at block545. For example, if the gain adjustment signal represents a decimated version of the low-range driver signal301as in the example ofFIG. 5, the gain adjustment signal may be upsampled back up to the sample rate of the driver signal301. In one aspect, the gain adjustment signal may also be smoothed through a lowpass filter to remove high-frequency noise, before being multiplied by the driver signal301.

Still referring toFIG. 5, the power mitigation algorithm may compute the first power budget dynamically, in that the first power budget is updated for each sequential window in which the low-range driver signal is gain-adjusted by the multiplier block545. To do so, the mitigation algorithm pay perform part of the full-range driver path312in blocks550-585to compute the average instantaneous power requirement of the full range audio amplifiers236in each window, similar to what the algorithm does for the low range audio amplifier235(in the low range driver path311as described above.) In one aspect, the following operations are performed on portions of the full-range driver signals302that correspond, in the sense of time, to the same portion (e.g., the sample) of the low-range driver signal301that is processed along the low-range driver path311, especially since the full-range driver signals302may be received or generated from the audio signal processing block210in synch with the low range driver signal301(seeFIG. 2).

Starting with block550, a portion (e.g., one sample) of each of the full-range driver signals is multiplied by a pre-determined gain, AmpGain, of its respective audio amplifier236, which drives a respective loudspeaker driver125to output the full-range driver signal, to produce a gain increased magnitude or voltage, V, signal. This voltage signal (of each full-range driver signal) is then divided by a load resistance value, Ld Resis, that corresponds to the resistance of its respective loudspeaker driver125, to produce a current, I, signal value (at block555). The current signal value is then multiplied by the voltage, V, signal pursuant to the relationship, Power=I*V, to produce the instantaneous power requirement that that is needed by the respective audio amplifier236to drive the respective loudspeaker driver125to output the full-range driver signal (at block560). These determined instantaneous power requirements for several loudspeaker drivers125are then combined (e.g., summed or added) together at block565, into a single, total instantaneous power. To improve accuracy, this total instantaneous power value is scaled, divided by a pre-defined amplifier efficiency value, AmpEff (at block570). Next, the quiescent power required by each of the audio amplifiers236, Qui Pwr, is added to the efficiency-adjusted total instantaneous power value (at block575). The result is a value that represents an accurate calculation of the total instantaneous power required by the audio amplifiers236to drive their respective loudspeaker drivers125to output one sample each of the several, full-range driver signals302, as more generally described in block315ofFIG. 3.

Operation continues with blocks580where several separate parallel processing paths are formed, each for one of several different windows, in which the total instantaneous power of the full range audio amplifiers236is computed for several sequential samples in a respective window (as described above.) In each path, a power value, Brd Budg Tav, is added that represents the power requirements of other system load elements (e.g., the system logical board202and/or other elements, such as LEDs) that draw power from or that complete the load on the power supply220. These other system load elements may be powered by the same voltage rail, here, the second voltage rail255as shown inFIG. 2, as the full range audio amplifiers236. In one aspect, the other power value that is added in each parallel path of the block580(representing for example the power consumption of the logic board and elements other than audio amplifiers) is the same regardless of the size of the respective window of that path. Alternatively, the other power values may vary based on the size of the window, to provide finer granularity or improved accuracy in the computation of the first power budget. In blocks585, an average of the resulting total instantaneous power values in each of the windows is then determined, as described more generally above in relation to block320ofFIG. 3. The outputs of the blocks585thus include the power consumption of the full range amplifiers236(and optionally here, the power consumption of the other system load elements that share the power supply voltage rail255) in the respective the windows, and are updated in sequential windows, thus enabling the determination of a dynamic, first power budget by block587of the low-range driver path311.

In each of blocks586, the output of a respective block585is subtracted from a constant output power rating of the power supply220on the voltage rail250, or power supply limit, PS V1 Lim, at a respective block587, to result in the first power budget in the respective window. These first power budget values (computed for on a per window basis) are then provided to the blocks530which as described above determine the difference between the average power and the first power budget for each window, leading eventually to block545where the gain adjustment process results in a mitigated, low-range driver signal.

Note that blocks586are optional and may be added to account for the less than 100% efficiency of a power converter, e.g., a buck converter, that is used to produce the power supply output voltage on the voltage rail255which may be different than what the low range amplifiers235use for their power supply, namely the voltage rail250. Therefore, the computed power at the output of each block585, for each window, is divided by an optional, pre-defined power converter efficiency value, BuckEff, that may vary for each window.

There is also an optional gain adjustment process that can be performed upon the full-range driver signals302, to produce the mitigated full-range driver signals inFIG. 5. These may proceed in the full-range driver path312beginning with blocks590and ending with block597where a second gain adjustment signal is applied to the full-range driver signals302. In each of the blocks590, a difference between i) the determined total power requirement for all of the full range amplifiers236(from the respective block585) and ii) a second power budget is determined. The second power budget may be represented by the power supply limit, PS V2 Lim, which may be the constant output power rating on the second voltage rail255(and that may be different for each window.) The result of each division in block590is a determined difference between the average total power requirement over a window and the second power budget in that window, as also described above in block340ofFIG. 3. The algorithm may clip or limit each of the differences in blocks595, to prevent any boost being applied to the full range driver signals302, similar to the operations performed at blocks535for the low range driver signal301. At block596, the algorithm then determines (e.g., selects) a second gain adjustment signal according to the largest difference, as described in block345ofFIG. 3. This signal is then multiplied by each of the full-range driver signals302, and then each of these gain adjusted full-range driver signals at block597, before being sent to its respective audio amplifier236for driving a loudspeaker driver125. In one aspect, this second gain adjustment signal may also be smoothed through a lowpass filter (not shown), before being multiplied by each of the full-range audio driver signals302at block597, to remove high-frequency noise.

In one aspect, since it may take time for the mitigation block215to process the two driver paths311,312, the low-range and full-range driver signals301,302may be delayed in buffers (not shown) before being multiplied by their respective gain adjustment signals at blocks545,597.

In one aspect, the determination of the first power budgets used to mitigate the low-range driver signal301(e.g., at block325, inFIG. 3) are dynamic and are based on “predicted” power requirements, or the power predicted to be needed to output the full-range audio driver signals302during the different windows. Thus, the actual power drawn by the full range amplifiers236to output the full-range driver signals302may be different than even the more accurately estimated average powers that are determined at blocks585ofFIG. 5. For further accuracy, a feedback path (not shown) may be added. For example, the power requirements determined at blocks585may be further adjusted according to the second gain adjustment signal that is multiplied by the full-range driver signals at block597, through this feedback path. In one aspect, the power requirements may be adjusted before being divided by the buck efficiency value at block586. In one aspect, to adjust the power requirements, the second gain adjustment signal is multiplied by each of the power requirements that are determined by the blocks585. There may be a conversion unit needed here to convert the second gain adjustment signal, which may be in voltage domain, into the power domain. Thus, in this scheme, the first power budget that is determined in blocks587(for each window) includes the difference between the constant output power rating of the power supply220, PS V1 Lim (in that window) and the adjusted (e.g., improved accuracy) version of the power requirement (in that window.)

It should be noted that in some aspects, variations of the processes described inFIGS. 2-5can be performed in which the specific operations are not performed in the exact order shown in the drawings or described above.

As previously explained, an aspect of the invention may be a non-transitory machine-readable medium (such as microelectronic memory) having stored thereon instructions, which program one or more data processing components (generically referred to here as a “processor”) to perform the audio signal processing operations and peak power mitigation operations described above. In other aspects, some of these operations might be performed by specific hardware components that contain hardwired logic. Those operations might alternatively be performed by any combination of programmed data processing components and fixed hardwired circuit components.