LD-CELP: a high quality 16 kb/s speech coder with low delay

Author

Chen, Juln-Hwey ; Cox, Richard V.

Author_Institution

AT&T Bell Lab., Murray Hill, NJ, USA

fYear

1990

fDate

2-5 Dec 1990

Firstpage

528

Abstract

The coder is basically a backward-adaptive version of the code-excited linear prediction (CELP) coder, and is named low-delay CELP, or LD-CELP. The low coding delay (less than 2 ms) is achieved by using backward-adaptive predictor and gain, and by using a small excitation vector size. This coder has been implemented in real-time using the AT&T DSP32C floating-point DSP chips. Currently the encoder uses about 90% of the processor time while the decoder takes about 40%. Fixed-point implementation of the coder is also possible with some modifications of the algorithm. The speech quality of 16 kb/s LD-CELP is approximately equivalent to that of the CCITT G.721 32 kb/s ADPCM (adaptive differential PCM) standard. The coder can pass 300, 1200, and 2400 b/s modem signals as well as DTMF (dual-tone multifrequency) tones. From the preliminary results of CCITT laboratory tests, it appears that this coder can meet all CCITT requirements for the 16 kb/s speech coding standard

Keywords

digital signal processing chips; encoding; filtering and prediction theory; speech analysis and processing; standards; vocoders; 1200 bit/s; 16 kbit/s; 2400 bit/s; 300 bit/s; AT&T; DSP32C floating-point DSP; DTMF tones; LD-CELP; backward-adaptive gain; backward-adaptive predictor; code-excited linear prediction; dual-tone multifrequency tones; fixed point implementation; laboratory tests; low coding delay; low-delay CELP; modem signals; processor time; small excitation vector size; speech coder; speech coding standard; speech decoder; speech processing; speech quality; vocoders; Code standards; Decoding; Delay; Digital signal processing chips; Laboratories; Modems; Phase change materials; Speech coding; Testing; Vectors;

fLanguage

English

Publisher

ieee

Conference_Titel

Global Telecommunications Conference, 1990, and Exhibition. 'Communications: Connecting the Future', GLOBECOM '90., IEEE

Conference_Location

San Diego, CA

Print_ISBN

0-87942-632-2

Type

conf

DOI

10.1109/GLOCOM.1990.116567

Filename

116567