Abstract: A method for performing packet loss concealment (PLC) and/or frame erasure concealment (FEC) in a speech decoder of a voice communication system. In accordance with the method, if a segment of an encoded speech signal is determined to be bad, an excitation signal is derived by scaling a random sequence of samples, and long-term and short-term predictive parameters are derived based on parameters associated with a previously-decoded segment. The excitation signal is then filtered by a long-term synthesis filter and a short-term synthesis filter under the control of the respective long-term and short-term predictive parameters. If the number of consecutively-received bad segments exceeds a predetermined threshold, the decoded speech signal is gradually reduced.

Abstract: A method of concealing bit errors in a signal is provided. The method comprises encoding a signal parameter according to a set of constraints placed on a signal parameter quantizer. The encoded signal parameter is decoded and compared against the set of constraints. Finally, the method includes declaring the decoded signal parameter invalid when the set of constraints is violated. Training binned ranges of gain values provide a threshold for selecting data segments to examine for violation of constraints on gain differences. Further, an additional method comprises training a threshold function T(qlg(m?1), ?qlg(m?1) used in a codec bit error detecting technique. The threshold function is based upon a first training file having N signal segments. The method includes encoding the first training file and determining gain values qlg(m) of each of the N signal segments within the encoded first training file. The gain values form a range and the range is divided into bins.

Abstract: In a Noise Feedback Coding (NFC) system having a corresponding ZERO-STATE filter structure, the first ZERO-STATE filter structure including multiple filters, a method of producing a ZERO-STATE response error vector. The method includes: (a) transforming the first ZERO-STATE filter structure to a second ZERO-STATE filter structure including only an all-zero filter, the all-zero filter having a filter response substantially equivalent to a filter response of the ZERO-STATE filter structure including multiple filters; and (b) filtering a VQ codevector with the all-zero filter to produce the ZERO-STATE response error vector corresponding to the VQ codevector.

Abstract: A system and method are provided for processing audio and speech signals using a pitch and voicing dependent spectral estimation algorithm (voicing algorithm) to accurately represent voiced speech, unvoiced speech, and mixed speech in the presence of background noise, and background noise with a single model. The present invention also modifies the synthesis model based on an estimate of the current input signal to improve the perceptual quality of the speech and background noise under a variety of input conditions. The present invention also improves the voicing dependent spectral estimation algorithm robustness by introducing the use of a Multi-Layer Neural Network in the estimation process. The voicing dependent spectral estimation algorithm provides an accurate and robust estimate of the voicing probability under a variety of background noise conditions. This is essential to providing high quality intelligible speech in the presence of background noise.

Abstract: A method of attempting to determine a pitch period of an audio signal using a correlation-based signal derived from the audio signal. The correlation-based signal has known peaks each corresponding to a respective one of known time lags. The method comprises: identifying a time lag among the time lags; determining if there exists another time lag (i) within a time lag range of a respective one of one or more integer multiples of the identified time lag, and (ii) corresponding to a peak exceeding a peak threshold; and if the determination of step (a) passes, then returning the identified time lag as a time lag indicative of the pitch period.

Abstract: A method of determining a pitch period of an audio signal using a correlation-based signal derived from the audio signal. The correlation-based signal includes known peaks each corresponding to a respective one of known time lags. The known peaks includes a global maximum peak. The method comprises: (a) determining if a candidate peak among the local peaks exceeds a peak threshold; (b) determining if a candidate time lag corresponding to the candidate peak is within a predetermined range of at least one integer sub-multiple of the time lag corresponding to the global maximum peak; and (c) setting the pitch period equal to the candidate time lag when the determinations of both steps (a) and (b) are true.

Abstract: A method of searching for an interpolated peak of a Normalized Correlation Square (NCS) signal derived from an audio signal, comprises: producing quadratically interpolated correlation (QIC) signal values at interpolated time lags; squaring each of the QIC signal values to produce square QIC signal values; producing an individual interpolated energy signal value corresponding to each of the square QIC signal values, wherein ratios of the square QIC signal values to their corresponding interpolated energy values represent interpolated NCS signal values; and selecting, as the interpolated peak, a largest interpolated NCS signal value among the interpolated NCS signal values without evaluating the ratios.

Abstract: In a Noise Feedback Coding (NFC) system having a corresponding ZERO-STATE filter structure, the first ZERO-STATE filter structure including multiple filters, a method of producing a ZERO-STATE response error vector. The method includes: (a) transforming the first ZERO-STATE filter structure to a second ZERO-STATE filter structure including only an all-zero filter, the all-zero filter having a filter response substantially equivalent to a filter response of the ZERO-STATE filter structure including multiple filters; and (b) filtering a VQ codevector with the all-zero filter to produce the ZERO-STATE response error vector corresponding to the VQ codevector.

Abstract: In a Noise Feedback Coding (NFC) system operable in a ZERO-STATE condition and a ZERO-INPUT condition, the NFC system including at least one filter having a filter memory, a method of updating the filter memory. The method comprises: (a) producing a ZERO-STATE contribution to the filter memory when the NFC system is in the ZERO-STATE condition; (b) producing a ZERO-INPUT contribution to the filter memory when the NFC system is in the ZERO-INPUT condition; and (c) updating the filter memory as a function of both the ZERO-STATE contribution and the ZERO-INPUT contribution.

Abstract: A filter controller processes a decoded speech (DS) signal. The DS signal has a spectral envelope including a first plurality of formant peaks having different respective amplitudes. The controller produces, from the DS signal, a spectrally-flattened DS signal that is a time-domain signal. The spectrally-flattened time-domain DS signal has a spectral envelope including a second plurality of formant peaks. Each of the second plurality of formant peaks approximately coincides in frequency with a respective one of the first plurality of formant peaks. Also, the second plurality of formant peaks have approximately equal respective amplitudes. Next, the controller derives, from the spectrally-flattened time-domain DS signal, a set of filter coefficients representative of a filter response that is to be used to filter the DS signal.

Abstract: A method of processing a decoded speech (DS) signal including successive DS frames, each DS frame including DS samples. The method comprises: adaptively filtering the DS signal to produce a filtered signal; gain-scaling the filtered signal with an adaptive gain updated once a DS frame, thereby producing a gain-scaled signal; and performing a smoothing operation to smooth possible waveform discontinuities in the gain-scaled signal.

Abstract: A method to eliminate discontinuities in an adaptively filtered signal includes filtering a beginning portion of a current signal frame using a past set of filter coefficients, thereby producing a first filtered frame portion. The method also includes filtering the beginning portion of the current signal frame using a current set of filter coefficients, thereby producing a second filtered frame portion. The method also includes modifying the second filtered frame portion with the first filtered frame portion so as to smooth a possible filtered signal discontinuity between the second filtered frame portion and a past filtered frame produced using the past filter coefficients.

Abstract: A method of performing an excitation Vector Quantization (VQ) in a Noise Feedback Coding environment involves reorganizing a calculation of an energy of an error vector for each of a plurality of candidate excitation vectors of a codebook. The energy of the error vector is a cost function that is minimized during a search of the codebook for a best candidate excitation VQ vector. The reorganization includes expanding a Mean Squared Error (MSE) term of the error vector, excluding an energy term that is invariant to the candidate excitation vector, and pre-computing energy terms of ZERO-STATE responses of the candidate excitation vectors that are invariant to sub-vectors of a subframe. Another method searches a signed codebook. Both methods use correlation techniques.

Abstract: A method and system are provided for synthesizing a number of corrupted frames output from a decoder including one or more predictive filters. The corrupted frames are representative of one segment of a decoded signal (sq(n)) output from the decoder. The method comprises determining a first preliminary time lag (ppfe1) based upon examining a predetermined number (K) of samples of another segment of the decoded signal and determining a scaling factor (ptfe) associated with the examined number (K) of samples when the first preliminary time lag (ppfe1) is determined. The method also comprises extrapolating one or more replacement frames based upon the first preliminary time lag (ppfe1) and the scaling factor (ptfe).

Abstract: A method and system are provided for synthesizing a corrupted frame output from a decoder including one or more predictive filters. The corrupted frame is representative of one segment of a decoded signal output from the decoder. The method comprises extrapolating a replacement frame based upon another segment of the decoded signal and substituting the replacement frame for the corrupted frame. Finally, the internal states of the filters are updated based upon the substituting.

Abstract: A method and system are provided for processing an extrapolated signal including a number of consecutive replacement frames. The method comprises attenuating a portion of the extrapolated signal when the extrapolated signal reaches a predetermined duration. The attenuating produces an output signal having an attenuated portion, wherein the output signal includes the number of consecutive replacement frames. Each of the consecutive frames within the attenuated portion is attenuated by applying an attenuation window with a starting magnitude value of approximately 1 and including a unique ending magnitude. The unique ending magnitudes decrease over time.

Abstract: A method and system are provided for removing discontinuities associated with synthesizing a corrupted frame output from a decoder including one or more predictive filters. The corrupted frame is representative of one segment of a decoded signal. The method comprises copying a first number of stored samples of the decoded signal in accordance with a time lag and a scaling factor, and calculating a first number of ringing samples output from at least one of the filters.

Abstract: A method of concealing bit errors in a signal is provided. The method comprises encoding a signal parameter according to a set of constraints placed on a signal parameter quantizer. The encoded signal parameter is decoded and compared against the set of constraints. Finally, the method includes declaring the decoded signal parameter invalid when the set of constraints is violated.

Abstract: A system and method of concealing bit errors in a signal are provided. An exemplary method detects bit errors in an input signal having at least a current signal segment and a previous signal segment. The previous signal segment has a log-gain value qlg(m−1) and immediately precedes the current signal segment. The method comprises estimating a level lvl(m−1) of the input signal and determining a log-gain value qlg(m) of the current signal segment within the input signal. The method also comprises determining a difference between the gain value of the current signal segment and the previous signal segment and determining whether the difference exceeds a threshold. wherein the threshold is adaptive to the input signal level.

Abstract: A system for performing a computationally efficient method of searching through N Vector Quantization (VQ) codevectors for a preferred one of the N VQ codevectors predicts a speech signal to derive a residual signal, derives a ZERO-INPUT response error vector common to each of the N VQ codevectors, derives N ZERO-STATE response error vectors each based on a corresponding one of the N VQ codevectors, and selects the preferred one of the N VQ codevectors based on the N ZERO-STATE response error vectors and the ZERO-INPUT response error vector.