Speech Research, Any Low Bit Rate Speech Coding Standards Below 2.4 kb/s?

I am PhD student researching low bit rate speech coders. Does anyone
know if there are any speech coding standards below 2.4 kb/s? If
there are any is the low bit rate achieved by harnessing additional
correlations over longer intervals, the downside of which is increased
delay, restricting the application domain to non-conversational forms?

Thanks

Keith

Learn to google. I just got 128 hits on "Ultra low-bit
vocoders". We made one that was 300bps.

The answer is yes. Latency takes a hit, but conversation is
easily handled. Also more efficient coding, check out
Vector Quantization.

--
Chip Wood




Does anyone
kb/s? If
additional
is increased
non-conversational forms?

> Does anyone

See: "A very low bit rate speech coder based on a recognition/synthesis
paradigm", Ki-Seung Lee; Cox, R.V. -- Speech and Audio Processing, IEEE
Transactions, July 2001
They claim a performance similar to 2.4kbps MELP using only 800bps.
Though it is restricted to a single speaker system, it is suited for
personalized communication systems.

Saurabh Prasad

Something worth looking at for VERY low bitrate transmission in the
reconstruction of speech from MFCC vectors.

People have shown that you can get the bitrate of MFCC vectors down to
about 800bps. I.e.

"Low bit-rate feature vector compression using transform coding and
non-uniform bit allocation
IEEE International Conference on Acoustics Speech and Signal Processing
(ICASSP)
B.P. Milner and X. Shao 2003"

It has also be shown that you can reconstruct the original speech quite
well from MFCC vectors.

"Clean speech reconstruction from noisy mel-frequency cepstral
coefficients using a sinusoidal model
IEEE International Conference on Acoustics Speech and Signal Processing
(ICASSP)
X. Shao and B.P. Milner 2003"

From: http://www.cmp.uea.ac.uk/Research/speechgroup/publications.php

Cheers

Alastair

Thanks for all the advice.

Keith

Yes, there's the MELPe standard at 1200 bps:
http://www.MELPe.com
and FAQ:
http://www.compandent.com/melpe_faq.htm

There are additional activities to standardize rates as low as 600 bps
and 300 bps, but those are not finalized standard yet.