Speech parameter encoder

• US 5,666,465 A
• Filed: 12/12/1994
• Issued: 09/09/1997
• Est. Priority Date: 12/10/1993
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Ozawa, Kazunori
• Primary Examiner(s): MacDonald, Allen R.
• Assistant Examiner(s): EDOUARD, PATRICK NESTOR
• Application Number:
  US08/355,295
• Time in Patent Office: 1,002 Days
• Field of Search: 395/2.38, 395/2.39, 395/2.29-2.31, 381/36, 381/40
• US Class Current: 704/222
• CPC Class Codes: G10L 19/07 Line spectrum pair [LSP] vocoders
• CPC Class Codes: G10L 2019/0013 Codebook search algorithms

Abstract

A speech parameter encoder capable of encoding spectrum parameters at a bit rate of 1 kb/s or less with comparatively small amount of operations and memory capacity. A spectrum parameter calculation unit 130 derives a spectrum parameter representing the spectrum envelope of a discrete input speech signal through division thereof into frames each having a predetermined time length. A weighted coefficient calculation unit 150 derives a weighted coefficient corresponding to an auditory masking threshold value through derivation thereof from the speech signal. A spectrum parameter quantization unit 160 receives the weighted coefficient and the spectrum parameter and quantizes the spectrum parameter through search of a codebook such as to minimize the weighting distortion based on the weighted coefficient.

Claims

1. A speech parameter encoder comprising:

a spectrum parameter calculation unit for deriving a spectrum parameter representing spectrum envelope of a discrete input speech signal through division thereof into frames each having a predetermined time length;

a weighted coefficient calculation unit for deriving a weighted coefficient derived from an auditory masking threshold value calculated through a linear transformation and a critical band spectrum for the speech signal; and

a spectrum parameter quantization unit for receiving the weighted coefficient and the spectrum parameter and quantizing the spectrum parameter through search of a codebook to minimize the weighting distortion based on the weighted coefficient.

2. The speech parameter encoder according to claim 1, wherein said weighted coefficient calculation unit derives a weighted coefficient from an auditory masking threshold value calculated through the linear transformation and the critical band spectrum for the spectrum parameter.

3. The speech parameter encoder according to claim 1, wherein said spectrum parameter calculation unit makes a non-linear transform of the spectrum parameter to meet auditory characteristics.

4. The speech parameter encoder according to claim 2, wherein the spectrum parameter calculation unit makes a non-linear transform of the spectrum parameter to meet auditory characteristics.

5. The speech parameter encoder according to claim 1, wherein said spectrum parameter calculation unit performs a linear transform of the spectrum parameter to meet auditory sense characteristics before the quantization of the spectrum parameter.

6. A speech parameter encoder comprising:

a buffer memory configured to receive a digitized speech signal and to store one frame of the speech signal, the one frame corresponding to a predetermined time length;

a spectrum parameter calculation unit coupled to the buffer memory and configured to read the digitized speech signal in the one frame, to calculate linear prediction coefficients for a predetermined degree as parameters representing spectrum characteristics of the speech signal, and to perform a transform of the linear prediction coefficients into a spectrum parameter;

a weighted coefficient calculation unit coupled to the spectrum parameter calculation unit and the buffer memory, the weighted coefficient calculation unit configured to derive an auditory masking threshold value from the speech signal and to derive a weighted coefficient from the derived auditory masking threshold value;

a codebook for storing a plurality of code vectors; and

a spectrum parameter quantization unit coupled to the codebook, the weighted coefficient calculation unit and the spectrum parameter calculation unit, the spectrum parameter quantization unit configured to receive the spectrum parameter and the weighted coefficient and to quantize the spectrum parameter through search of the code vectors in the codebook so as to minimize a weighting distortion based on the weighted coefficient.

7. The speech parameter encoder according to claim 6, wherein the weighted coefficient calculation unit comprises:

a fourier transform unit for performing a fourier transform on the speech signal and to output a transformed speech signal as a result;

a power spectrum calculation unit coupled to the fourier transform unit and configured to calculate a power spectrum of the transformed speech signal and to output a power spectrum signal a result;

a critical band spectrum calculation unit coupled to the power spectrum calculation unit and configured to calculate a critical band spectrum power for each critical band of the power spectrum signal, wherein the power spectrum signal spans at least a plurality of critical bands in a frequency domain, each critical band being contiguous in frequency with an adjacent critical band, the critical band spectrum calculation unit further providing a convolution of the critical band spectrum power with a spreading function so as to generate a spreading signal as a result;

a masking threshold value spectrum calculation unit coupled to the critical band spectrum calculation unit and configured to compute a masking threshold value spectrum by multiplying the spreading signal with a masking threshold value and to determine a maximum of the multiplied result and an absolute threshold value so as to generate a masking threshold signal as a result; and

a weighted coefficient unit coupled to the masking threshold value spectrum calculation unit and configured to derive the spectrum parameter by transformation of the masking threshold signal from a Burke axis to a Hertz axis.