Voice-excited predictive coding system for low-bit-rate transmission of speech
Bishnu Saroop Atal, V. Stover · The Journal of the Acoustical Society of America · 1975
Voice-excited speech analysis synthesis systems eliminate two of the most difficult tasks in speech analysis, namely, voiced-unvoiced decision and pitch analysis. They can therefore perform better than pitch-excited systems under practical speaking conditions. However, the transmission rates for voice-excited systems are usually much higher than for pitch-excited systems, owing to the additional bits needed for encoding the baseband. This disadvantage can be overcome by efficient encoding of the baseband. This paper presents a voice-excited predictive coding method for speech transmission at 2400 to 3600 bps. The analytic signal corresponding to a baseband of 300 to 900 Hz is square-rooted to reduce its bandwidth to 300 Hz and is encoded at 1200 bps by predictive coding. At the receiver, the wide-band excitation is derived by nonlinear distortion and inverse-filtering of the baseband. The speech signal is sampled at 6.67 kHz, and its spectral-envelope information is transmitted every 20 msec by 10 area parameters obtained by the linear prediction method. These parameters and the rms value of the speech signal are encoded at 1800 bps, yielding a transmission rate of 3000 bps for the speech signal.