Data processing: speech signal processing – linguistics – language – Speech signal processing – For storage or transmission
Patent
1996-09-18
1999-09-07
Hudspeth, David R.
Data processing: speech signal processing, linguistics, language
Speech signal processing
For storage or transmission
704219, G10L 502
Patent
active
059501553
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a speech encoding method for encoding short-term prediction residuals or parameters representing short-term prediction coefficients of an input speech signal by vector or matrix quantization.
BACKGROUND ART
There are a variety of encoding methods known for encoding an audio signal, inclusive of a speech signal and an acoustic signal, by exploiting statistical properties of the audio signal in the time domain and in the frequency domain and the psychoacoustic characteristics of the human hearing system. These encoding methods may be roughly classified into encoding on the time domain, encoding on the frequency domain and analysis/synthesis encoding.
If, in multi-band excitation (MBE), single-band excitation (SBE), harmonic excitation, sub-band coding (SBC), linear predictive coding (LPC), discrete cosine transform (DCT), modified DCT (MDCT) or fast Fourier transform (FFT), as examples of high-efficiency coding for speech signals, various information data, such as spectral amplitudes or parameters thereof, such as LSP parameters, .alpha.-parameters or k-parameters, are quantized, scalar quantization has been usually adopted.
If, with such scalar quantization, the bit rate is decreased to e.g. 3 to 4 kbps to further increase the quantization efficiency, the quantization noise or distortion is increased, thus raising difficulties in practical utilization. Thus it is currently practiced to group different data given for encoding, such as time-domain data, frequency-domain data or filter coefficient data, into a vector, or to group such vectors across plural frames, into a matrix, and to effect vector or matrix quantization, in place of individually quantizing the different kinds of data.
For example, in code excitation linear prediction (CELP) encoding, LPC residuals are directly quantized by vector or matrix quantization as time-domain waveform. In addition, the spectral envelope in MBE encoding is similarly quantized by vector or matrix quantization.
If the bit rate is decreased further, it becomes infeasible to use enough bits to quantize parameters specifying the envelope of the spectrum itself or the LPC residuals, thus deteriorating the signal quality.
In view of the foregoing, it is an object of the present invention to provide a speech encoding method capable of affording satisfactory quantization characteristics even with a smaller number of bits.
DISCLOSURE OF THE INVENTION
With the speech encoding method according to the present invention, a first codebook and a second codebook are formed by assorting parameters representing short-term prediction values concerning a reference parameter comprised of one or a combination of a plurality of characteristic parameters of the input speech signal. The short-term prediction values are generated based upon the input speech signal. One of the first and second codebooks concerning the reference parameter of the input speech signal is selected and the short-term prediction values are quantized by referring to the selected codebook for encoding the input speech signal.
The short-term prediction values are short-term prediction coefficients or short-term prediction errors. The characteristic parameters include the pitch values of the speech signal, pitch strength, frame power, voiced/unvoiced discrimination flag and the gradient of the signal spectrum. The quantization is the vector quantization or the matrix quantization. The reference parameter is the pitch value of the speech signal. One of the first and second codebooks is selected in dependence upon the magnitude relationship between the pitch value of the input speech signal and a pre-set pitch value.
According to the present invention, the short-term prediction value, generated based upon the input speech signal, is quantized by referring to the selected codebook for improving the quantization efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram showing a speech encoding device (encoder) as an illustrative example of a device fo
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Hudspeth David R.
Maioli Jay H.
Sofocleous M. David
Sony Corporation
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