[Speex-dev] Developement speex; harmonic booster

H B creativecontest at hotmail.com
Mon May 4 20:21:05 PDT 2009

An idea would be like for WMA 9 lower bitrates (32-42-48Kbps) to use a 'crystallizer'; which is basically a harmonics booster focussed at transposing sharp tones some octaves higher.


A file has been recorded @ 20khz computer (or 10khz real life) to preserve space.

While playing back the file sounds a bit mushy, almost as if someone was speaking through a cardboard wall. The higher frequencies are missing, and you can easily perceive that the file is a low bitrate file.


By harmonically transposing frequencies from 6 to 10Khz with one octave, and overlaying the original file with that stream, one can create the perception that an additional stream of 12-20Khz has been encoded. This effect is extremely usefull since altered (or artificial) frequencies below 100Hz and above 6Khz are enormously hard to hear!

Especially in speech!

In music this would translate to that the cymbals of all songs or drums sound about the same, and one can clearly pick the original recording from the compressed one.

But for voice this is hardly noticable since very few articulated tones actually go over 10Khz. 

The letter 'S' and 'C' are two of them.


By this a much higher quality is perceivable (on low bitrates), the software only needs to be included in the decoder, and technically could still work with older compressed Speex files.


I just wanted to throw in this idea, since it works quite nice on WMA; and for now I'm encoding speech files with 48kbps (speech with background music) or 32kbps (speech as being preaching, bookreading or lectures).

I wish to see that number going down though. If Speex performs better, has smaller files, and can compete with 32kbps WMA9 encoded files, I might become interested in testing out the product, and perhaps switching over!

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