[opus] low pass filter frequency adjustable

Benjamin Schwartz benjamin.m.schwartz at gmail.com
Sun Jan 27 14:47:27 PST 2013

Opus is a single-purpose codec for audio going into human ears.  Humans
ears can't hear above 20 kHz, so Opus can't code higher frequencies.  Lower
frequencies may be modified based on the human psychoacoustic model.

When you need to store frequencies above 20 kHz, your audio must not be
headed directly for human ears, so Opus is probably not a good choice.
(Neither is any other lossy music or speech codec.)  In those cases I
recommend you stick with something like FLAC.

On Sun, Jan 27, 2013 at 10:40 AM, Mike Kaplan <Mike.Kaplan at gmx.com> wrote:

> Hi, recently I made some test with the opus tools (enc and dec) and I'm
> very (and positively) surprised about the resultant quality. But the
> only think that I miss is the ability to change the low pass filter
> frequency via "--lowpass" option or similar. For example at a quality or
> 96 kbps the cut off of the filter starts at 16Khz and is completely cut
> at 20 Khz. But in case of testing or adjusting streams for special
> purposes would be good the possibility of change the frequency both
> above 20Khz and below 20Khz (or other).
> I guess that the cut-off frequency is specified somewhere in the code,
> so should not be hard to add this optionvia command line. I hope that
> the developers take this into account in future versions.
> ---
> Mike
> _______________________________________________
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> opus at xiph.org
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