A low-delay CELP coder for the CCITT 16 kb/s speech coding standard

Chen, J.-H.; Cox, R.V.; Lin, Yu Ching; Jayant, N.; Melchner, Melvin J.

doi:10.1109/49.138988

Cited by 165 publications

(45 citation statements)

References 32 publications

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“…It is well known that codecs using backward adaption for both the LTP delay and gain are very sensitive to bit errors, and this is why LTP was not used in G.728 [19]. Thus, as expected, we found that Codec B gave a very poor performance, when subjected to even a relatively low bit error rate (BER).…”

Section: The Error Sensii'ivity Of the Low Delay Codecsmentioning

confidence: 60%

“…The G.728 codec [19,20] uses a frame-length of five samples or 0.625 ms, with 10 bits being used to encode each five-sample frame, giving a bit rate of 16 kbitds. Backward adaption is used to derive the short-term filter coefficients at both the encoder and the decoder, and hence, no bits need to be transmitted to specify the filter coefficients used.…”

Section: Four Low Delay Codecs Operating Between 8 Aivd 4 Kbits/smentioning

confidence: 99%

“…In 1992 a low delay 16 kbitsls CELP codec was developed by the AT&T speech compression team and standardised by the CCITT as G.728 [19,201. This codec uses backward adaption (BA) to determine the linear prediction coefficients which are used in the encoding and decoding of the speech.…”

Section: Lh@ecssotonacukmentioning

confidence: 99%

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A Range of Low and High Delay CELP Speech Codecs between 8 and 4 kbits/s

Woodard

Hanzo

1997

Digital Signal Processing

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(1997), 37-46. In this paper we study the performance and the error sensitivities of six CELP [I] based codecs operating between 8 and 4 kbitsls. Codecs using both forward and backward adaption of the linear prediction coefficients and the long term predictor (LTP) are described. Initially we describe four low delay codecs which all use backward adaption of the LPC coefficients but which differ in their use of LTP. These codecs all have frame-lengths of 3 ms or less, and their performance at various bit rates between 8 and 4 kbitafs is examined. Next the error sensitivity of these codecs, and means of improving it, are described. Then an algebraic CELP (ACELP) [2] codec operating at 6.2 kbitsfs with a frame-length of 5 ms is described. Our final codec also uses ACELP and operates between 4.7 and 7.1 kbitsls, but it is forward adaptive and so it has a much longer frame-length of up to 30 ms. After describing this codec we compare the performance of our codecs in both error-he conditions and in the presence of channel errors. Surprisingly the error sensitivity of the low delay backward adaptive codec with no Lll' is similar to that of the forward adaptive, high delay,ACELP codec. e 1997 Academic Press

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Section: The Error Sensii'ivity Of the Low Delay Codecsmentioning

confidence: 60%

Section: Four Low Delay Codecs Operating Between 8 Aivd 4 Kbits/smentioning

confidence: 99%

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A Range of Low and High Delay CELP Speech Codecs between 8 and 4 kbits/s

Woodard

Hanzo

1997

Digital Signal Processing

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“…Low delay is achieved by the use of a backward-adaptive predictor and short excitation vectors (5 samples each) [3]. Only the index of the excitation codebook is transmitted -all other parameters are updated by backward adaptation of previously quantized speech.…”

Section: B Low Delay Code Excited Linear Prediction Algorithmmentioning

confidence: 99%

“…lookup tables with codevectors corresponding to speech residual signals [2], [3]. In Mixed Excitation Linear Prediction (MELP) [4], an additional classification of speech is introduced -the jittery voiced speech.…”

Section: Introductionmentioning

confidence: 99%