Abstract:
A speech enhancement system controls the gain of an excitation signal to prevent uncontrolled gain adjustments. The system includes a first device that converts sound waves into operational signals. An ambient noise estimator is linked to the first device and an echo canceller. The ambient noise estimator estimates how loud a background noise would be near the first device before or after an echo cancellation. The system then compares the ambient noise estimate to a current ambient noise estimate near the first device to control a gain of an excitation signal.

Description:
PRIORITY CLAIM 
       [0001]    This application is a continuation-in-part of U.S. Ser. No. 12/428,811, entitled “Robust Downlink Speech and Noise Detector,” filed Apr. 23, 2009; and is a continuation-in-part of U.S. Ser. No. 11/644,414, entitled “Robust Noise Estimation,” filed Dec. 22, 2006; and claims the benefit of priority from U.S. Ser. No. 61/055,913 entitled “Ambient Noise Compensation System Robust to High Excitation Noise,” filed May 23, 2008, all of which are incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    This disclosure relates to ambient noise compensation, and more particularly to an ambient noise compensation system that prevents uncontrolled gain adjustments. 
         [0004]    2. Related Art 
         [0005]    Some ambient noise estimation involves a form of noise smoothing that may track slowly varying signals. If an echo canceller is not successful in removing an echo entirely, this may not affect ambient noise estimation. Echo artifacts may be of short duration. 
         [0006]    In some cases the excitation signal may be slowly varying. For example, when a call is made and received between two vehicles. One vehicle may be traveling on a concrete highway, perhaps it is a convertible. High levels of constant noise may mask or exist on portions of the excitation signal received and then played in the second car. This downlink noise may be known as an excitation noise. An echo canceller may reduce a portion of this noise, but if the true ambient noise in the enclosure is very low, then the residual noise may remain after an echo canceller processes. The signal may also dominate a microphone signal. Under these circumstances, the ambient noise may be overestimated. When this occurs, a feedback loop may be created where an increase in the gain of the excitation signal (or excitation noise) may cause an increase in the estimated ambient noise. This condition may cause a gain increase in the excitation signal (or excitation noise). 
       SUMMARY 
       [0007]    A speech enhancement system controls the gain of an excitation signal to prevent uncontrolled gain adjustments. The system includes a first device that converts sound waves into operational signals. An ambient noise estimator is linked to the first device and an echo canceller. The ambient noise estimator estimates how loud a background noise would be near the first device prior to an echo cancellation. The system then compares the ambient noise estimate to a current ambient noise estimate near the first device to control a gain of an excitation signal. 
         [0008]    Other systems, methods, features, and advantages will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the following claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]    The system may be better understood with reference to the following drawing and descriptions. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figure, like referenced numerals designate corresponding parts throughout the different views. 
           [0010]      FIG. 1  is an ambient noise compensation system. 
           [0011]      FIG. 2  is an excitation signal process. 
           [0012]      FIG. 3  is a noise compensation process. 
           [0013]      FIG. 4  illustrates contributions to noise received at an input. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    Ambient noise compensation may ensure that audio played in an environment may be heard above the ambient noise within that environment. The signal that is played may be speech, music, or some other sound such as alerts, beeps, or tones. The signal may also be known as an excitation signal. Ambient noise level may be estimated by monitoring signal levels received at a microphone that is within an enclosure into which the excitation signal may be played. A microphone may pick up an ambient noise and an excitation signal. Some systems may include an echo canceller that reduces the contribution of the excitation signal to the microphone signal. The systems may estimate the ambient noise from the residual output of the microphone. 
         [0015]    Some systems attempt to estimate a noise level near a device that converts sound waves into analog or digital signals (e.g., a microphone) prior to processing the signal through an echo canceller. The system may compare (e.g., through a comparator) this estimate to the current ambient noise estimate at the microphone, which may be measured after an echo cancellation. If the excitation noise played out or transmitted into the environment is expected to be of lower magnitude than the ambient noise (e.g.,  FIG. 4C ), then a feedback may not occur. If the excitation noise is expected to be of a higher magnitude than the ambient noise (e.g.,  FIG. 4A  and Figure &amp;  4 B:  405  vs.  415 ), then a feedback may occur. The feedback may depend on how much louder the excitation noise is and how much the excitation noise may be expected to be reduced by an echo canceller. For example, if the echo canceller may reduce a signal by 25 dB and the expected excitation noise is only 10 dB higher than the ambient noise estimate (e.g.,  405  in  FIG. 4C ), and then the system may be programmed to conclude that the noise estimated is the ambient cabin noise. The system programming may further conclude that the ambient cabin noise includes no (or little) contribution from the excitation signal. If an expected excitation noise is more than 20 dB or so than the ambient noise estimate (e.g.,  405  in  FIG. 4A ) then it is possible, even likely, for the system&#39;s programming to conclude that part or all of the noise estimated is the excitation noise and its signal level does not represent the a true ambient noise in the vehicle. 
         [0016]    When a situation like the one described above occurs, a flag is raised or a status marker may be set to indicate that the excitation noise is too high. The system may determine that further increases in gain made to the excitation signal should not occur. In addition, if any gain currently being made to the excitation signal prior to the signals transmission to an enclosure (e.g., in a vehicle) through an amplifier/attenuator then the current gain may also be reduced until the flag or status indicator is cleared. 
         [0017]    The programming may be integrated within or may be a unitary part of an ambient noise compensation system of  FIG. 1 . A signal from some source may be transmitted or played out through a speaker into an acoustic environment and a receiver such as a microphone or transducer may be used to measure noise within that environment. Processing may be done on the input signal (e.g., microphone signal  200 ) and the result may be conveyed to a sink which may comprise a local or remote device or may comprise part of a local or remote device that receives data or a signal from another device. A source and a sink in a hands free phone system may be a far-end caller transceiver, for example. 
         [0018]    In some systems, the ambient noise compensation is envisioned to lie within excitation signal processing  300  shown in  FIG. 2 . In  FIG. 2 , the excitation signal may undergo several operations before being transmitted or played out into an environment. It may be DC filtered and/or High-pass filtered and it may be analyzed for clipping and/or subject to other energy or power measurements or estimates, as at  310 . 
         [0019]    In some processes, there may be voice and noise decisions made on the signal, as in  320 . These decisions may include those made in the systems and methods described in U.S. Ser. No. 12/428,811, entitled “Robust Downlink Speech and Noise Detector” filed Apr. 23, 2009, which is incorporated by reference. Some processes know when constant noise is transmitted or being played out. This may be derived from Noise Decision  380  described in the systems and methods described in the “Robust Downlink Speech and Noise Detector” patent application. 
         [0020]    There may be other processes operating on the excitation signal, as at  330 . For example, the signal&#39;s bandwidth may be extended (BWE). Some systems extend bandwidth through the systems and methods described in Ser. No. 11/317,761, entitled “Bandwidth Extension of Narrowband Speech” filed Dec. 23, 2005, and/or Ser. No. 11/168,654, entitled “Frequency Extension of Harmonic Signals” filed Jun. 28, 2005, both of which is incorporated by reference. Some systems may compensate for frequency distortion through an equalizer (EQ). The signal&#39;s gain may then be modified in Noise Compensation  340  in relation to the ambient noise estimate from the microphone signal processing  200  of  FIG. 2 . Some systems may modify gain through the systems and methods described in U.S. Ser. No. 11/130,080, entitled “Adaptive Gain Control System” filed May 16, 2005, which is incorporated by reference. 
         [0021]    In some processes, the excitation signal&#39;s gain may be automatically or otherwise adjusted (in some applications, through the systems and methods described or to be described) and the resulting signal limited at  350 . In addition, the signal may be given as a reference to echo cancellation unit  360  which may then serve to inform the process of an expected level of the excitation noise. 
         [0022]    In the noise compensation act  340 , a gain is applied at  345  (of  FIG. 3 ) to the excitation signal that is transmitted or played out into the enclosure. To prevent a potential feedback loop, logic may determine whether the level of pseudo-constant noise on the excitation signal is significantly higher than the ambient noise in the enclosure. To accomplish this, the process may use an indicator of when noise is being played out, as in  341 . This indicator may be supplied by a voice activity detector or a noise activity detector  320 . The voice activity detector may include the systems and methods described in U.S. Ser. No. 11/953,629, entitled “Robust Voice Detector for Receive-Side Automatic Gain Control” filed Dec. 10, 2007, and/or Ser. No. 12/428,811, entitled “Robust Downlink Speech and Noise Detector” filed Apr. 23, 2009, both of which are incorporated by reference. 
         [0023]    If a current excitation signal is not noise then the excitation signal may be adjusted using the current noise compensation gain value. If a current signal is noise, then its magnitude when converted by the microphone/transducer/receiver may be estimated at  342 . The estimate may use a room coupling factor that may exist in an acoustic echo canceller  360 . This room coupling factor may comprise a measured, estimated, and/or pre-determined value that represents the ratio of excitation signal magnitude to microphone signal magnitude when only excitation signal is playing out into the enclosure. The room coupling factor may be frequency dependent, or may be simplified into a reduced set of frequency bands, or may comprise an averaged value, for example. The room coupling factor may be multiplied by the current excitation signal (through a multiplier), which has been determined or designated to be noise, and the expected magnitude of the excitation noise at the microphone may be estimated. 
         [0024]    Alternatively, the estimate may use a different coupling factor that may be resident to the acoustic echo canceller  360 . This alternative coupling factor may be an estimated, measured, or pre-determined value that represents the ratio of excitation signal magnitude to the error signal magnitude after a linear filtering device stage of the echo canceller  360 . The error coupling factor may be frequency dependent, or may be simplified into a reduced set of frequency bands, or may comprise an averaged value. The error coupling factor may be multiplied by the current excitation signal (through a multiplier), which has been determined to be noise, or by the excitation noise estimate, and the expected magnitude of the excitation noise at the microphone may be estimated. 
         [0025]    The process may then determine whether an expected level of excitation noise as measured at the microphone is too high. At  344  the expected excitation noise level at the microphone at  342  may be compared to a microphone noise estimate (such as described in the systems and methods of U.S. Ser. No. 11/644,414 entitled “Robust Noise Estimation,” which is incorporated by reference) that may be completed after the acoustic echo cancellation. If an expected excitation noise level is at or below the microphone noise level, then the process may determine that the ambient noise being measured has no contribution from the excitation signal and may be used to drive the noise compensation gain parameter applied at  345 . If however the expected excitation noise level exceeds the ambient noise level, then the process may determine that a significant portion of raw microphone signal comes is originating from the excitation signal. The outcomes of these occurrences may not occur frequently because the linear filter that may interface or may be a unitary part of the echo canceller may reduce or effectively remove the contribution of the excitation noise, leaving a truer estimate of the ambient noise. If the expected excitation noise level is higher than the ambient noise estimate by a predetermined level (e.g., an amount that exceeds the limits of the linear filter), then the ambient noise estimate may be contaminated by the excitation noise. To be conservative some systems apply a predetermined threshold, such as about 20 dB, for example. So, if the expected excitation noise level is more than the predetermined threshold (e.g., 20 dB) above the ambient noise estimate, a flag or status marker may be set at  344  to indicate that the excitation noise is too high. The contribution of the excitation to the estimated ambient noise may also be made more directly using the error coupling factor, described above. 
         [0026]    If an excitation noise level is too high then the noise compensation gain that is being applied to the excitation signal may be reduced at  343  to prevent a feedback loop. Alternatively, further increases in noise compensation gain may simply be stopped while this flag is set (e.g., or not cleared). This prevention of gain increase or actual gain reduction may be accomplished several ways, each of which may be expected to similarly prevent the feedback loop. 
         [0027]    The methods and descriptions of  FIGS. 1-3  may be encoded in a signal bearing medium, a computer readable storage medium such as a memory that may comprise unitary or separate logic, programmed within a device such as one or more integrated circuits, or processed by a controller or a computer. If the methods are performed by software, the software or logic may reside in a memory resident to or interfaced to one or more processors or controllers, a wireless communication interface, a wireless system, an entertainment and/or comfort controller of a vehicle or types of non-volatile or volatile memory remote from or resident to a speech enhancement system. The memory may retain an ordered listing of executable instructions for implementing logical functions. A logical function may be implemented through digital circuitry, through source code, through analog circuitry, or through an analog source such through an analog electrical, or audio signals. The software may be embodied in any computer-readable medium or signal-bearing medium, for use by, or in connection with an instruction executable system, apparatus, device, resident to a hands-free system or communication system or audio system and/or may be part of a vehicle. In alternative systems the computer-readable media component may include a firmware component that is implemented as a permanent memory module such as ROM. The firmware may programmed and tested like software, and may be distributed with a processor or controller. Firmware may be implemented to coordinate operations of the processor or controller and contains programming constructs used to perform such operations. Such systems may further include an input and output interface that may communicate with an automotive or wireless communication bus through any hardwired or wireless automotive communication protocol or other hardwired or wireless communication protocols. 
         [0028]    A computer-readable medium, machine-readable medium, propagated-signal medium, and/or signal-bearing medium may comprise any medium that includes, stores, communicates, propagates, or transports software for use by or in connection with an instruction executable system, apparatus, or device. The machine-readable medium may selectively be, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. A non-exhaustive list of examples of a machine-readable medium would include: an electrical or tangible connection having one or more wires, a portable magnetic or optical disk, a volatile memory such as a Random Access Memory “RAM” (electronic), a Read-Only Memory “ROM,” an Erasable Programmable Read-Only Memory (EPROM or Flash memory), or an optical fiber. A machine-readable medium may also include a tangible medium upon which software is printed, as the software may be electronically stored as an image or in another format (e.g., through an optical scan), then compiled by a controller, and/or interpreted or otherwise processed. The processed medium may then be stored in a local or remote computer and/or machine memory. 
         [0029]    Other alternate systems and methods may include combinations of some or all of the structure and functions described above or shown in one or more or each of the figures. These systems or methods are formed from any combination of structure and function described or illustrated within the figures or incorporated by reference. Some alternative systems interface or include the systems and methods described in Ser. No. 11/012,079, entitled “System for Limiting Receive Audio” filed Dec. 14, 2004 as the context dictates, which is incorporated by reference. Some alternative systems are compliant with one or more of the transceiver protocols may communicate with one or more in-vehicle displays, including touch sensitive displays. In-vehicle and out-of-vehicle wireless connectivity between the systems, the vehicle, and one or more wireless networks provide high speed connections that allow users to initiate or complete a communication or a transaction at any time within a stationary or moving vehicle. The wireless connections may provide access to, or transmit, static or dynamic content (live audio or video streams, for example). As used in the description and throughout the claims a singular reference of an element includes and encompasses plural references unless the context clearly dictates otherwise. 
         [0030]    While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.