Speech coding system

• US 20020184005A1
• Filed: 04/04/2002
• Published: 12/05/2002
• Est. Priority Date: 04/09/2001
• Status: Active Grant

• Current Assignee: Callahan Cellular LLC (Intellectual Ventures LLC)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Gigi, Ercan Ferit
• Granted Patent: US 7,050,967 B2
• Time in Patent Office: Days
• US Class Current: 704/201
• 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: H04B 14/068 with adaptive feedback

Abstract

In a speech coding system with an encoder and a decoder cooperating with said encoder, the speech encoder comprises a pre-processor and an ADPCM encoder with a quantizer and step-size adaptation means, while the speech decoder comprises an ADPCM decoder with similar step-size adaptation means as in the ADPCM encoder and with a decoder, and a post-processor. The quantizer is provided with storage means containing values for a correction factor α(c(n)) of the step-size Δ(n), said correction factor being dependent on the quantizer output signal c(n). The step-size adaptation occurs in accordance with the relation: $\Delta \left(n+1\right)=\Delta \left(n\right)·A·\{\begin{array}{cc}\alpha \left(c\left(n\right)\right)& \mathrm{if}\alpha \left(c\left(n\right)\right)<1\\ \alpha \left(c\left(n\right)\right)+b& \mathrm{if}\Delta \left(n\right)·A·c_{\max }<{\Delta }_{\max }\\ 1& \mathrm{otherwise}\end{array}$

Claims

1. Speech coding system with a speech encoder and a speech decoder cooperating with said speech encoder, the speech encoder comprising a pre-processor and an ADPCM (adaptive differential pulse code modulation) encoder with a quantizer and step-size adaptation means and the speech decoder comprising an ADPCM decoder with similar step-size adaptation means as in the ADPCM encoder and with a decoder, and a post-processor, the quantizer being provided with storage means containing values for a correction factor α

(c(n)) of the step-size Δ

(n), said correction factor being dependent on the quantizer output signal c(n),

characterized in that the step-size adaptation occurs in accordance with the relation;

2. Speech coding system according to claim 1, characterized in that the storage means in the quantizer contain values of correction factors α

(c(n)) in accordance with the tables in any one of the FIGS. 3A-3F.

3. Speech coding system according to claim 1 or 2, characterized in that the correction factors α

(c(n)) are adapted for a coding system, wherein in the pre-processor phase-smearing filter means are applied and in the post-processor inverse phase-smearing filter means.