Kazuyuki Iijima

Voice encoding method and apparatus using modified discrete cosine transform

A method and apparatus for encoding an input signal, such as a broad-range speech signal, in which a number of decoding operations with different bit rates are enabled for assuring a high encoding bit rate and for minimizing deterioration of the reproduced sound even with a low bit rate. The signal encoding method includes a band-splitting step for splitting an input signal into a number of bands and a step of encoding signals of the bands in a different manner depending on signal characteristics of the bands. Specifically, a low-range side signal is taken out by a low-pass filter from an input signal entering a terminal, and analyzed for Linear Predictive coding by an Linear Predictive coding analysis quantization unit. After finding the Linear Predictive coding residuals, as short-term prediction residuals by an Linear Predictive coding inverted filter, the pitch is found by a pitch analysis circuit. Then, pitch residuals are found by long-term prediction by a pitch inverted filter. The pitch residuals are processed with modified discrete cosine transform by a modified discrete cosine transform (MDCT) circuit and vector-quantized by a vector-quantization circuit. The resulting quantization indices are transmitted along with the pitch lag and the pitch gain. The linear spectral pairs linear spectral pairs are also sent as parameter representing LPC coefficients.

Method and apparatus for speech encoding and decoding by sinusoidal analysis and waveform encoding with phase reproducibility

A speech encoding method and apparatus in which an input speech signal is divided in terms of blocks or frames as encoding units and encoded in terms of the encoding units, whereby explosive and fricative consonants can be impeccably reproduced, while there is an attenuation of the occurrence of foreign sounds being generated at a transient portion between voiced (V) and unvoiced (UV) portions, so that the speech with high clarity devoid of “stuffed” feeling may be produced. The encoding apparatus includes a first encoding unit for finding residuals of linear predictive coding (LPC) of an input speech signal for performing harmonic coding and a second encoding unit for encoding the input speech signal by waveform coding. The first encoding unit and the second encoding unit are used for encoding a voiced (V) portion and an unvoiced (UV) portion of the input signal, respectively. Code excited linear prediction (CELP) encoding employing vector quantization by a closed loop search of an optimum vector using an analysis-by-synthesis method is used for the second encoding unit. A corresponding decoding method and apparatus is also provided.