A synthesizer for a channel vocoder for the transmission of speech with considerable frequency band reduction in digital technology provides a reduction of circuit expense. This is accomplished, given non-recursive filters having finite impulse response, not with a weighting of the pulse-shaped excitation variable with the transmitted envelope values of the spectral channels, but with a time variance of the filters by weighting their filter coefficients with the transmitted envelope values. In addition, with proper dimensioning of the filter coefficients, an optimum speech quality of synthesized speech is obtained at the output of the synthesizer even given elimination of the transmission of a voiced/voiceless signal.

Input signals representative of speech are unreliable as inputs for speech recognition if processed conventionally by, among other processes, filtering into separate frequency bands. Further processing according to the invention takes the output from a filter bank and after operations of rectification and integration provides a process of median filtering and smoothing which significantly reduces the sampling rate of the filtered signals while retaining the important acoustic features of the input speech.

A level measuring circuit first measures a level of an input speech signal. Next, a coefficient calculating circuit determines a value for suppressing a change of the level of the input speech signal on the basis of an output of the level measuring circuit. Then an input speech signal delay circuit delays the input speech signal by a time required for processing in the level measuring circuit and the coefficient calculating circuit. Finally a multiplying circuit multiplies an output of the input speech signal delay circuit by an output of the coefficient calculating circuit to obtain an output speech signal in which changes in level of the input speech signal are suppressed.

Disclosed is a signal processor formed using digital waveguide networks. The digital waveguide networks have signal scattering junctions. A junction connects two waveguide sections together or terminates a waveguide. The junctions are constructed from conventional digital components such as multipliers, adders, and delay elements. The signal processor of the present invention is typically used for digital reverberation and for synthesis of reed, string or other instruments.

The disclosed invention takes advantage of the fact that the speech information and processing needed for successful animation lip-synching is actually much less than the information and processing which is needed for identifying individual words, as in the traditional speech recognition task, The disclosed embodiment utilizes linear prediction to obtain speech parameters which can be used to identify phonemes from a limited set corresponding to visually distinctive mouth positions. In the disclosed embodiment there is set forth an apparatus for producing lip-synching for a spoken sound track. Means are provided for storing, for each of a number of mouth positions, an unvoiced phonetic information representation associated with a mouth position. Means, responsive to samples of sound from the sound track, are provided for generating unvoiced phonetic information signals for the samples. Further means are provided for comparing the unvoiced phonetic information signals with the stored unvoiced phonetic information representations to determine which of the stored representations most closely matches the unvoiced phonetic information signals. The determined representations are then stored in time correspondence with the sound track.