DETECTING AND QUANTIFYING NON-LINEAR CHARACTERISTICS OF AUDIO SIGNALS
Methods, systems, and apparatuses are provided for detecting, quantifying, and compensating for non-linear characteristics of audio signals. External audio devices are detected when coupled to electronic or communication devices. Tuning operations are initiated upon detection of external audio devices to estimate non-linear parameters imparted to audio signals by the external audio devices. The non-linear components of audio signals are compensated for based upon the estimations. Compensation is performed using pre-processing filters, distortion circuits, post-processing filters. Estimation and compensation for non-linearities is performed on the basis of models dynamically generated during estimation and the use of higher-order statistics.
1 . A method in a phone terminal for performing acoustic echo cancellation for telephony systems configured to connect to external amplifiers or speakers, comprising:
detecting that an external audio amplifier has been coupled to the phone terminal;
dynamically detecting an acoustic non-linearity introduced in a first audio signal by the external audio amplifier being coupled to the phone terminal;
estimating at least one non-linear parameter associated with the acoustical non-linearity in response to the detection; and
compensating for the detected acoustic non-linearity in the first audio signal based at least upon the at least one estimated non-linear parameter to generate an echo-cancelled audio signal.
2 . The method of claim 1 , further comprising:
generating an indication to a user that a tuning operation is to be performed in response to detecting that the external audio amplifier is coupled to the phone terminal; and
initiating the tuning operation.
3 . The method of claim 1 , wherein compensating comprises at least one of:
performing a linearization of the external audio amplifier using a pre-distortion circuit, or
removing at least a portion of the acoustic non-linearity using a pre-processing echo canceller.
4 . The method of claim 1 , further comprising:
providing an audio test signal to the external audio amplifier to cause at least one loudspeaker coupled to the audio amplifier to broadcast sound;
receiving the broadcast sound by at least one microphone of the phone terminal;
generating a return signal based on the received broadcast sound; and
performing an analysis of the return signal.
5 . The method of claim 4 , wherein said performing an analysis of the return signal comprises:
performing at least one of
a third-order statistical cross-correlation analysis between the audio test signal and the return signal to generate a third-order cross-correlation,
a third-order statistical cross-bispectrum analysis between the audio test signal and the return signal to generate a third-order cross-bispectrum, or
an additional third-order statistical analysis between the audio test signal and the return signal.
6 . The method of claim 5 , wherein said providing an audio test signal to the external audio amplifier to cause at least one loudspeaker coupled to the audio amplifier to broadcast sound comprises:
providing a Gaussian signal as the test signal; and
wherein said dynamically detecting further comprises:
detecting the acoustic non-linearity by analyzing the third-order cross-correlation and the third-order cross-bispectrum.
7 . The method of claim 5 , wherein said providing an audio test signal to the external audio amplifier to cause at least one loudspeaker coupled to the audio amplifier to broadcast sound comprises:
providing a series of tones, each tone comprising at least one frequency, amplitude, or phases that is different from each other tone, as the test signal; and
wherein said estimating further comprises:
estimating the at least one non-linear parameter by analyzing the third-order cross-correlation and the third-order cross-bispectrum at a plurality of frequencies.
8 . The method of claim 4 , further comprising at least one of:
estimating a bulk delay associated with the phone terminal and the coupled external audio amplifier;
estimating an energy imbalance between a left audio channel and a right audio channel; or
adding one or more TAPs to reduce an algorithmic delay associated with one or more of said dynamically detecting, said estimating, or said compensating.
9 . The method of claim 1 , wherein at least one of said dynamically detecting, said estimating, or said compensating is performed in accordance with a memoryless non-linearity associated with one or more of at least one small loudspeaker and at least one memoryless analog device, or a memory-based non-linearity associated with one or more of at least one large loudspeaker and at least one memory-based analog device.
10 . A phone terminal, comprising:
an amplifier detector configured to detect that an external audio amplifier has been coupled to the phone terminal;
a non-linearity detector configured to dynamically detect an acoustic non-linearity introduced in a first audio signal by the external audio amplifier being coupled to the phone terminal;
a non-linearity estimator configured to estimate at least one non-linear parameter associated with the acoustical non-linearity in response to the detection; and
a non-linearity compensator configured to compensate for the detected acoustic non-linearity in the first audio signal based at least upon the at least one estimated non-linear parameter to generate an echo-cancelled audio signal.
11 . The phone terminal of claim 10 , wherein the amplifier detector is further configured to:
generate an indication to a user that a tuning operation is to be performed in response to detecting that the external audio amplifier is coupled to the phone terminal; and
wherein the phone terminal further comprises:
one or more processors configured to initiate a tuning operation.
12 . The phone terminal of claim 10 , wherein the non-linearity compensator comprises at least one of:
a pre-distortion circuit configured to perform a linearization of the external audio amplifier, or
a pre-processing echo canceller configured to remove the acoustic non-linearity.
13 . The phone terminal of claim 12 , further comprising:
an audio output device configured to provide an audio test signal to the external audio amplifier to cause at least one loudspeaker coupled to the audio amplifier to broadcast sound;
at least one microphone configured to receive the broadcast sound by at least one microphone of the phone terminal; and
one or more processors configured to generate a return signal based on the received broadcast sound;
wherein at least one of the non-linearity detector or the non-linearity estimator is configured to perform an analysis of the return signal.
14 . The phone terminal of claim 13 , wherein at least one of the non-linearity detector or the non-linearity estimator is configured to perform the analysis of the return signal by performing at least one of:
a third-order statistical cross-correlation analysis between the audio test signal and the return signal to generate a third-order cross-correlation,
a third-order statistical cross-bispectrum analysis between the audio test signal and the return signal to generate a third-order cross-bispectrum, or
an additional third-order statistical analysis between the audio test signal and the return signal.
15 . The phone terminal of claim 14 , wherein the audio output device is further configured to:
provide a Gaussian signal as the test signal; and
wherein the non-linearity detector is further configured to:
detect the acoustic non-linearity by analyzing the third-order cross-correlation and the third-order cross-bispectrum.
16 . The phone terminal of claim 14 , wherein the audio output device is further configured to:
provide a series of tones with different frequencies as the test signal; and
wherein the non-linearity estimator is further configured to:
estimate the at least one non-linear parameter by analyzing the third-order cross-correlation and the third-order cross-bispectrum at a plurality of frequencies.
17 . The phone terminal of claim 13 , wherein at least one of the one or more processors is configured to perform at least one of:
implement at least one signal filter that includes one or more TAPs to reduce an algorithmic delay;
estimate a bulk delay associated with the phone terminal and the coupled external audio amplifier, or
estimate an energy imbalance between a left audio channel and a right audio channel.
18 . The phone terminal of claim 10 , wherein at least one of the non-linearity detector, the non-linearity estimator or the non-linearity compensator is configured to operate in accordance with a memoryless non-linearity associated with one or more of at least one small loudspeaker and at least one memoryless analog device, or a memory-based non-linearity associated with one or more of at least one large loudspeaker and at least one memory-based analog device.
19 . A computer-readable storage medium having computer-executable instructions recorded thereon for causing a processing device of a phone terminal to execute a method for performing acoustic echo cancellation, the method comprising:
detecting that an external audio amplifier has been coupled to the phone terminal;
dynamically detecting an acoustic non-linearity introduced in a first audio signal by the external audio amplifier being coupled to the phone terminal;
estimating at least one non-linear parameter associated with the acoustical non-linearity in response to the detection; and
compensating for the detected acoustic non-linearity in the first audio signal based at least upon the at least one estimated non-linear parameter to generate an echo-cancelled audio signal.
20 . The computer-readable storage device of claim 19 , the method further comprising:
generating an indication to a user that a tuning operation is to be performed in response to detecting that the external audio amplifier is coupled to the phone terminal;
providing an audio test signal to the external audio amplifier to cause at least one loudspeaker coupled to the audio amplifier to broadcast sound;
receiving the broadcast sound by at least one microphone of the phone terminal;
generating a return signal based on the received broadcast sound; and
performing an analysis of the return signal, comprising at least one of:
a third-order statistical cross-correlation analysis between the audio test signal and the return signal to generate a third-order cross-correlation, or
a third-order statistical cross-bispectrum analysis between the audio test signal and the return signal to generate a third-order cross-bispectrum.