Showing papers on "Code-excited linear prediction published in 1978"

Linear predictive coding of speech signals in a high ambient noise environment

Abstract: Preservation of both the spectral distribution and the periodicity of speech signals are essential in speech processing. This paper describes a method of speech coding in a high ambient noise environment and shows that the spectral envelope of speech signal is a most reliable information when the noise reduction method proposed in this paper is used. Also reported in this paper comparisons of several pitch extraction methods with extensive experimental data, based on which a pitch extraction method suited for noisy speech signals is proposed.

Research on low bit rate speech coding at the Electrical Communication Laboratory, NTT

Abstract: Since the introduction of speech analysis—synthesis based on the maximum likelihood spectrum estimation—in 1966, we have been conducting research activities on low bit rate speech coding techniques, and their aplication to audio response and low bit rate digital speech transmission. Parcor analysis‐synthesis, demonstrated in 1969, was one of the most fundamental methods, and it has formed the basis of the present development of linear predictive coding. Recently, various kinds of techniques have been proposed to improve speech quality, such as interpolation and nonlinear quantization of parameters, spectral smoothing, etc. They have been applied in the hardware realization of a 4 CH multiplexed 2400 bps Vocoder. At present, the Parcor method is being applied to a wide range of speech coding from 1200 bps variable frame‐rate coding to high quality 16 kbps adaptive, predictive coding.

Linear prediction techniques in the Walsh spectral domain for speech analysis and synthesis

Abstract: A method for LPC analysis in a transformed domain (LPCTD) has been developed theoretically and studied experimentally in the Walsh-Hadamard domain (LPCWHD) for low-bit- rate coding of speech signals . Speech signals in the Walsh-Hadamard domain have been modelled by their largest variance coefficients and a few prediction coefficients which represent the remaining coefficients. Determination of the prediction coefficients has been based on the correlation between the spectral coefficients. Intelligible speech at bit-rates of 8 kb/s and 4 kb/s was achieved when 16 and 64 point Walsh-Hadamard transforms were used, respectively. At the latter bit-rate the quality was significantly improved when unvoiced sounds were coded seperately by their largest variance coefficients. The main advantage of LPCWHD system is its simplicity which can lead to a far less complex implementation than that of vocoder systems.

A Low-Rate Digital Formant Vocoder

Abstract: A complete algorithm of a 1200-bits/s digital formant vocoder system is described. This vocoder algorithm draws heavily on the results of recent research in linear predictive coding. The transmitting parameters are frequencies and amplitudes of the first three formants, the pitch period, voiced/unvoiced decision, and the gain. Formant bandwidths are estimated at the synthesizer by using the amplitude information. The synthesizer structure is in the parallel form. The synthetic speech quality at 1200 bits/s is reasonably good; most of the speech is intelligible and speaker-recognizable.