Abstract: A low bit rate phase excited linear prediction type speech encoder filters a speech signal to limit its bandwidth and then fragments the filtered speech signal into speech segments. The speech segments are decomposed into a spectral envelope and an LP residual signal. The spectral envelope is represented by LP filter coefficients. The LP filter coefficients are converted into line spectral frequencies (LSF). Each speech segment is also classified as one of a voiced segment and an unvoiced segment based on a pitch of the segment. Parameters are extracted from the LP residual signal, where for an unvoiced segment the extracted parameters include pitch and gain and for a voiced segment the extracted parameters include pitch, gain and excitation level. The extracted parameters are then quantized.

Abstract: A low bit rate phase excited linear prediction type speech encoder filters a speech signal to limit its bandwidth and then fragments the filtered speech signal into speech segments. The speech segments are decomposed into a spectral envelope and an LP residual signal. The spectral envelope is represented by LP filter coefficients. The LP filter coefficients are converted into line spectral frequencies (LSF). Each speech segment is also classified as one of a voiced segment and an unvoiced segment based on a pitch of the segment. Parameters are extracted from the LP residual signal, where for an unvoiced segment the extracted parameters include pitch and gain and for a voiced segment the extracted parameters include pitch, gain and excitation level. The extracted parameters are then quantized.

Abstract: An apparatus and method of reconstructing a linear prediction synthesis filter excitation signal, by: receiving a signal representative of output from a linear prediction synthesis filter, producing therefrom a deterministic signal comprising a magnitude spectrum (50) and a phase spectrum (52); and producing (54) the reconstructed excitation signal from the deterministic signal and a noise signal.

Abstract: Data, such as digitally coded speech signals, is transmitted so that, for each of successive frame periods, bits are formatted into a frame sequence. The bits are coded using convolutional coding. Error check bits are generated using (a) bits formatted into the first 50% of the frame sequence and (b) bits formatted into the last 25% of the frame sequence.

Abstract: Data are coded with a first error correcting code to produce first coded bits. Control data are coded using a heavily redundant second error corrected code and added modulo 2 to the first coded bits. Decoding is performed by ascertaining which valid codeword of the second code (when added to the received codeword) gives the lowest error count when the resultant is decoded according to the first code.

Abstract: A codebook excited speech coder analyzes speech to produce coefficients of a synthesis filter, the parameters of a long-term prediction filter (LTP) and a codeword indication one of a set of excitations. The results are transmitted to a receiver where they can be used to resynthesize the speech. The LTP and excitation analysis involve generation of impulse response products by adding additional terms to products already formed and storing them in a store. Multiplication of these products by excitation terms is performed using a pointer table storing precalculated addresses of locations in the store. If some excitations are shifted versions of others, some addresses can be obtained by modifying other addresses. The LTP analysis may include selection between a simple delay prediction and a prediction including the sum of two differently delayed terms, to provide improved predictor delay resolution.

Abstract: Received signals are processed to generate bit confidence measure signal values. Before these are forwarded to a soft decision decoder, correction factors are applied, e.g., by a look-up table, to reduce the extent to which the signal statistics differ from a logarithmic representation of the error statistics of the received signals. Alternatively, or as well, the bit confidence measure signal values may be summed and thresholded to provide a quality-indicating signal.