Digital code converter

Details Digital code converter Digital code converter

1982-12-27

1984-10-02

Safourek, Benedict V.

Pulse or digital communications

Repeaters

Testing

340347DD, H04L 2516

Patent

active

044752130

ABSTRACT:
Accumulation of distortion possibly resulting from multiple digital code conversions is prevented by including in an ADPCM-to-PCM decoder (100, FIG. 1 or 600, FIG. 6) an arrangement (119, FIG. 1 or 601, FIG. 6) for making a trial transmission of the resulting PCM sample (.PSI.(k)) to obtain (via 209, FIG. 2) a composite noise value (.alpha.(k)) for the PCM sample (.PSI.(k)). The composite noise value includes noise components resulting from both quantizing the code word and truncating digital signals used in the decoder and subsequent coder. The composite noise value is evaluated (via 211) to determine whether adjustment of the PCM sample value (.PSI.(k)) is necessary.
In one embodiment (FIG. 1, 100), a reconstructed linear version (Y.sub.r (k)) of the PCM sample is adjusted (via 216, 218, 220 or 221) when the composite noise value (.alpha.(k)) is not within the ADPCM quantizer interval for the ADPCM sample (I.sub.n (k)) being converted to PCM. The amount of adjustment is dependent on the PCM quantizer interval (214) that the reconstructed signal (Y.sub.r (k)) falls in and whether the ADPCM sample is in saturation, i.e., the most positive (215) or negative (217) ADPCM quantizer interval, or not in saturation (219).
In another embodiment (FIG. 6, 600), the decoder (600) PCM output sample (.PSI.(k)) is adjusted, if necessary, up or down one PCM quantizer interval (via 802 or 803) when the composite noise value (.alpha.(k)) is not within the quantizer interval decision levels of the ADPCM sample received by the decoder 600.

REFERENCES:
patent: 4179659 (1979-12-01), Tashiro
patent: 4296412 (1981-10-01), Mastner
patent: 4323885 (1982-04-01), Carriere et al.
patent: 4363024 (1982-12-01), Brokaw
patent: 4384278 (1983-05-01), Benjamin
Johnson et al., "Adaptive Rate Delta Modulator", IBM TDB, vol. 15, No. 11, Apr. 1973, pp. 3338-3341.
Narayanasami et al., "A Design Technique for Nonuniform Quantizer in PCM Generation", IEEE Trans. on Circuits and Systems, vol. CAS-29, No. 3, Mar. 1982, pp. 193-196.
"A Low Noise ADPCM-LOG PCM Code Converter", by Hideyo Murakami, 1979 International Symposium on Circuits and Systems Proceedings, IEEE Cat. No. 79 CH1421-7 CAS, pp. 969-970, Jul. 17-19, 1979.
"Proposal for a Transcoding Algorithm", CCITT-Q.7/XVIII, Expert Group on 32 kbit/s Codecs, Dec. 1982, pp. 1-10, Japan, Discussed in the Specification.

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