Voice coding apparatus

• US 5,003,604 A
• Filed: 03/09/1989
• Issued: 03/26/1991
• Est. Priority Date: 03/14/1988
• Status: Expired due to Fees

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Unnagami, Shigeyuki, Amano, Fumio, Okazaki, Koji, Ohta, Yasuji
• Primary Examiner(s): KEMENY, EMANUEL
• Application Number:
  US07/321,153
• Time in Patent Office: 747 Days
• Field of Search: 381/49, 381/36, 381/38
• US Class Current: 704/207
• CPC Class Codes: G10L 19/00 Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis in musical instruments G10H
• CPC Class Codes: G10L 25/90 Pitch determination of speech signals

Abstract

A voice coding apparatus includes a pitch detecting circuit which detects a pitch period of a voice signal; a pitch waveform generating circuit which samples the voice signal for a plurality of pitches based on the pitch period detected by the pitch detecting circuit and which generates a waveform of one pitch from the waveform of the plurality of pitches; a band restriction circuit which restricts the frequency band of the one pitch waveform generated in the pitch waveform generating circuit; and a coding circuit for coding the voice waveform which is band restricted in the band restriction circuit. The sampling number of the waveform for a plurality of pitches and the restricted bandwidth can be changed in accordance with the amount of the pitch period extracted in the pitch detecting circuit. Further, the pitch detecting circuit is able to correctly detect the pitch period even when the pitch period is not a multiple of the sampling period.

Claims

1. A voice coding apparatus comprising:

pitch detecting means for detecting a pitch period T of a voice signal;

pitch waveform generating means for sampling the voice signal based on the pitch period T and for generating a pitch voice waveform responsive to said sampling;

band restriction means for restricting the frequency band of the pitch voice waveform based on the pitch period T; and

coding means for coding the band restricted pitch voice waveform;

thereby changing, in accordance with the amount of the pitch period extracted in said pitch detecting means the sampling of said pitch voice waveform generating means and the frequency band of the band restricted pitch voice waveform.

2. A voice coding apparatus according to claim 1, wherein said pitch waveform generating means includes:

a first input terminal connectable to receive the voice signal;

a second input terminal operatively connected to receive the pitch period T;

means for, when the pitch period T is longer than 15 msec, providing the pitch voice waveform based on sampling the voice signal using a factor of three; and

means for, when the pitch period is shorter than 15 msec, providing the pitch voice waveform based on sampling the voice waveform using a factor of seven.

3. A voice coding apparatus according to claim 1, wherein said band restriction means comprises:

band division filter for dividing the output of said pitch waveform generating means into a high frequency pitch voice waveform and a low frequency pitch voice waveform, and wherein said coding means comprises;

first encoder means for coding the low frequency pitch voice waveform;

second encoder means for coding the high frequency pitch voice waveform;

switch means, operatively connected to said second encoder means and to receive the pitch period T information, for providing the high frequency pitch voice waveform when T<

15 msec.

4. A voice coding apparatus according to claim 1, wherein said pitch detecting means comprises:

pitch extraction means for extracting a virtual pitch period (T(d)) of the voice signal;

discrete Fourier transformation means for performing a discrete Fourier transformation on the voice signal using the pitch period (T(d)) as a frame length; and

multiple pitch detecting means for determining if the discrete Fourier transformation of the voice signal is a linear spectrum and for detecting a true pitch period (T) of the voice signal based on the determination.

5. A voice coding apparatus comprising

pitch extraction means for receiving an input voice signal and for extracting a virtual pitch period (T(d)) of the input voice signal;

pitch waveform generating means for sampling the input voice signal based on the virtual pitch period (T(d)) and for generating a pitch voice waveform using the sampled input voice signal;

discrete Fourier transformation means for performing a discrete Fourier transformation on the voice input signal using the virtual pitch period (T(d)) as a frame length and for providing an output responsive to the discrete Fourier transformation;

multiple pitch detecting means for determining if the discrete Fourier transformation of the voice input signal is a linear spectrum;

divider means for providing a pitch period T based on the virtual pitch period (T(d)) and the determination of said multiple pitch detecting means;

band restricting means for restricting the frequency band of the output of said discrete Fourier transformation means based on the virtual pitch period (T(d)) and for providing a band restricted output; and

coding means for coding the band restricted output.