Speech coding apparatus capable of implementing acceptable in-channel transmission of non-speech signals

A speech coding apparatus comprising:

• a discriminator for deciding as to whether the input signal is a speech signal or a non-speech signal;
• a frequency parameter generator for outputting, when the input signal is the speech signal, frequency parameters that indicate characteristics of a frequency spectrum of the speech signal, and for outputting, when the input signal is the non-speech signal, frequency parameters obtained by correcting frequency parameters that indicate characteristics of a frequency spectrum of the non-speech signal;
• a quantization codebook for storing codewords of a predetermined number of frequency parameters;
• and
• a quantizer for selecting codewords corresponding to the frequency parameters output from said frequency parameter generating means by referring to said quantization codebook;
• and
• a selector for selecting a codeword that will minimize quantization distortion from a plurality of codewords, wherein
• said frequency parameter generator comprises a corrector for correcting the frequency parameters of the non-speech signal when the input signal is the non-speech signal, said corrector including one of three sets consisting of a plurality of correcting sections, a plurality of bandwidth expansion sections and a plurality of white noise superimposing sections, said correcting sections correcting the frequency parameters of the non-speech signal with different interpolation characteristics between the frequency parameters of the input signal and frequency parameters of white noise, said bandwidth expansion sections carrying out bandwidth expansion of the non-speech signal by different characteristics, and said white noise superimposing sections superimposing different level white noises on the input signal, and said frequency parameter generator generates the frequency parameters of a plurality of non-speech signal streams from the outputs of the corrector;
• said quantizer includes a plurality of quantization sections for selecting codewords corresponding to the frequency parameters of the non-speech signal streams, and for outputting the codewords with quantization distortions at that time;
• and
• said selector selects codeword that will minimize quantization distortion from the plurality of codewords selected by said quantization sections.

A speech coding apparatus for coding an input signal consisting of one of a speech signal and a voice-band non-speech signal, said speech coding apparatus comprising:

• a discriminator for deciding as to whether the input signal is a speech signal or a non-speech signal;
• a frequency parameter generator for generating frequency parameters that indicate characteristics of a frequency spectrum of the input signal;
• a quantization codebook for storing codewords of a predetermined number of frequency parameters;
• at least one codebook subset including a subset of the codewords stored in the quantization codebook;
• a quantizer for selecting, when said input signal is the speech signal, codewords corresponding to the frequency parameters of the input signal by referring to said quantization codebook, and for selecting, when said input signal is the non-speech signal, codewords corresponding to the frequency parameters of the input signal by referring to said codebook subset;
• a codeword selector for adaptively selecting, from among the codewords in said quantization codebook, codewords with small quantization distortion involved in quantizing the frequency parameters of the non-speech signal, wherein said codebook subset includes the codewords output from said codeword selector;
• and
• a second frequency parameter generator for generating frequency parameters by interpolating between the frequency parameters of the input signal and frequency parameters of white noise, wherein
• said codeword selector quantizes the frequency parameters generated by said second frequency parameter generator, and selects the codewords of said codebook subset considering quantization distortion involved in the quantization.

A speech coding method for coding input signals including at least one speech signal and at least one voice-band non-speech signal, said method comprising:

• classifying each of the input signals as speech or non-speech;
• obtaining frequency parameters characterizing a frequency spectrum for each of the classified input signals;
• and
• referring to a common quantization codebook to select codewords corresponding to the frequency parameters obtained for both the input signals classified as speech and non-speech,
• wherein the obtaining frequency parameters further comprises:
• for each of the input signals classified as non-speech, performing the following:
• interpolating frequency parameters between the frequency parameters of the input signal and frequency parameters of white noise;
• and
• replacing the frequency parameters of the input signal with the interpolated frequency parameters.