| Paper: | SP-P5.15 (ICASSP 2003 Paper) | ||
| Session: | Topics in Speech Coding | ||
| Time: | Wednesday, May 19, 09:30 - 11:30 | ||
| Presentation: | Poster (ICASSP 2003 Presentation) | ||
| Topic: | Speech Processing: Narrowband Speech Coding | ||
| Title: | HYBRID MELP/CELP CODING AT BIT RATES FROM 6.4 TO 2.4 kb/s | ||
| Authors: | Jacek Stachurski; Texas Instruments, Inc. | ||
| Alan McCree; Texas Instruments, Inc. | |||
| Vishu Viswanathan; Texas Instruments, Inc. | |||
| Ari Heikkinen; Nokia Research Center | |||
| Anssi Ramo; Nokia Research Center | |||
| Sakari Himanen; Nokia Research Center | |||
| Peter Bloecher; Ericsson Eurolab | |||
| Abstract: | This paper describes extensions of the 4 kb/s hybrid MELP/CELPcoder, up to 6.4 kb/s and down to 2.4 kb/s. The baseline4 kb/s coder uses three coding modes: MELP in strongly voicedspeech frames, CELP with pitch prediction in weakly voicedframes, and CELP with stochastic excitation in unvoicedframes. To minimize switching artifacts between parametricMELP and waveform CELP coding, an alignment phase is encodedin MELP and zero-phase equalization is applied to the CELPtarget signal. The 6.4 kb/s extension uses the same threemodes as the 4 kb/s coder, with improved MELP and CELP coders.The 2.4 kb/s extension uses only two modes: MELP for voicedframes and CELP synthesis with random excitation for unvoicedframes. The alignment phase is encoded in MELP frames for allbit rates so that time synchrony with input speech is alwaysmaintained. Alignment phase and zero-phase equalizationenable smooth switching between coders at different bit rates.The hybrid MELP/CELP coding structure leads to coders thatperform better at a given bit rate than MELP or CELPseparately, and better than or equivalent to higher bit-rateITU standards. Formal subjective tests show that forall-but-one tested conditions, the 6.4 kb/s hybrid coder isbetter than 8 kb/s G.729 and the 2.4 kb/s coder is equivalentto, or better than, 6.4 kb/s G.729 Annex D. | ||
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