| 摘要 |
An implementation of the present invention for 4800 bits per second comprises a voice encoder and decoder method and system that uses voice excitation, eliminating the voice/unvoiced pitch tracking, and the first formant up to 2400 Hertz, does not use pulse code modulation encoding, but uses the zero crossings only of the first formant, dividing by two and sampling at 2400 Hertz. The resulting combination uses half of the bit rate for excitation and the remainder for short term spectrum analysis. The spectrum is updated each 20.8 milliseconds using 50 bits per frame. The decoder extracts the excitation, multiplies it by two and uses a Hanning modified sawtooth and spectral flattening to excite the spectrum generator. This waveform produces both even and odd harmonics for both periodic (voiced) and aperiodic (unvoiced) frequencies and gives naturalness to all languages and speakers. The technique for 2400 bits per second utilizes first formant up to 1100 Hertz heterodyning down by 300 Hertz, dividing by tow and sampling at 800 Hertz. The short term power spectrum uses a difference encoding to give a frame of 36 bits which is sent at 44.4 Hertz rate. The demultiplexed excitation is then heterodyned to the original frequency, where it is then used to excite the decoded short term spectrum and the resultant is naturally sounding speech. Both 4800 BPS and 2400 BPS excitation is delayed by one frame before it is used to stimulate the short term power spectrum inverse filters.
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