Abstract: A communications system (100) includes a multi-rate source coder (MRSC) (102), a variable size/rate buffer (VSRB) (112), a speech buffer (104), and a buffer control block (106). The variable size/rate buffer (112) includes a source coder bit buffer (SCBB) (114) and an adaptive transmit frame buffer (116). The source coder bit buffer (114) receives speech frames coded at different rates from the multi-rate source coder (102), and deposits an integer or non-integer number of frames in the adaptive transmit frame buffer (ATFB) (116). A receiver includes a seamless rate transition module (SRTM) (308) and an variable buffer (310). The seamless rate transition module (308) correlates speech data previously coded at different rates, and it then truncates or alternatively appends, concatenates, and warps the speech data to remove any annoying artifacts at the rate change boundary.

Abstract: A method and apparatus (100) for pitch-epoch-synchronous source-filter speech encoding by means of error component modeling methods (310) which capture fundamental orthogonal (uncorrelated) basis elements of an excitation source waveform. A periodic waveform model (318) along with four orthogonal error waveforms, desirably including phase error (319), ensemble error (321), standard deviation error (323), and mean error (324) waveforms, are incorporated together to form a complete description of the excitation. These error waveforms (319,321, 323, 324) represent those portions of the excitation that are not represented by the purely periodic model. By thus orthogonalizing the error components, the perceptual effect of each element is isolated from the composite set, and can thus be encoded separately.

Abstract: A speech coder (100) computes scalar statistics (180), ensemble statistics (190), spectral parameters (150), and a normalized excitation waveform (270) which describe a frame of speech samples. The coder (100) encodes the statistics (220, 230), spectral parameters (155), and the normalized waveform (290) for later decoding and synthesis. A speech synthesizer (900) decodes the encoded scalar statistics (570), encoded ensemble statistics (560), encoded spectral parameters (490), and encoded normalized excitation waveform (550). The synthesizer (900) then denormalizes (670) the normalized excitation waveform using the scalar statistics and the ensemble statistics, resulting in a decoded excitation waveform. Speech is synthesized (710) from the decoded excitation waveform and the decoded spectral parameters.