Abstract: An improved noise reduction algorithm is provided, as well as a voice activity detector, for use in a voice communication system. The voice activity detector allows for a reliable estimate of noise and enhancement of noise reduction. The noise reduction algorithm and voice activity detector can be implemented integrally in an encoder or applied independently to speech coding application. The voice activity detector employs line spectral frequencies and enhanced input speech which has undergone noise reduction to generate a voice activity flag. The noise reduction algorithm employs a smooth gain function determined from a smoothed noise spectral estimate and smoothed input noisy speech spectra. The gain function is smoothed both across frequency and time in an adaptive manner based on the estimate of the signal-to-noise ratio. The gain function is used for spectral amplitude enhancement to obtain a reduced noise speech signal.

Abstract: An parametric speech codec; such as a CELP, RELP, or VSELP codec; is integrated with an echo canceler to provide the functions of parametric speech encoding, decoding, and echo cancellation in a single unit. The echo canceler includes a convolution processor or transversal filter that is connected to receive the synthesized parametric components, or codebook basis functions, of respective send and receive signals being decoded and encoded by respective decoding and encoding processors. The convolution processor produces and estimated echo signal for subtraction from the send signal. In order to process the synthesized parametric components having distinct basis functions in the convolution processor, conversion means are provided for providing the receive-side parametric component to the processor, or for providing the estimated echo signal, in terms of the send-side parameter. Plural convolution processors are provided for processing respective parametric components of the desired coding scheme.