[speex-dev] Higher Bandwidth at lower quality settings

Jean-Marc Valin jean-marc.valin at hermes.usherb.ca
Wed Feb 26 21:22:25 PST 2003

> 	I was wondering if anyone has experimented with Speex's wideband (16kHz)
> mode at lower quality settings.  In particular I have been using quality 3,
> and with wideband input files the resultant frequency spectrum is limited to
> about an upper end around 3.5kHz (almost telephony quality bandwidth).  Has
> anyone tried increasing the spectral bandwidth at the expense of lowering
> the narrowband quality (ie using two very low bitrate codebooks, one for
> narrowband and one for the 4-8kHz band - to match the same bitrate at
> quality 3)? If you have can you comment on the quality?  (Looking through
> the Speex code, I noticed that at lower quality settings wideband mode
> basically reverts to narrowband.)

I'm really not sure what you mean. In wideband mode, both the low-band
(0-4 kHz) and the high-band (4-8 kHz) are encoded even at low bit-rates.
When encoding below a certain bit-rate, the high-band becomes a rough
approximation, but it's still there.


Jean-Marc Valin, M.Sc.A.
LABORIUS (http://www.gel.usherb.ca/laborius)
Université de Sherbrooke, Québec, Canada

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