[opus] Antw: Re: Q: Bandwidth vs. bitrate

Emily Bowman silverbacknet at gmail.com
Thu Oct 31 08:27:21 UTC 2019

56kbps isn't even remotely low as a bitrate for Opus or for speech in
general. If you really pushed it, like asking for 12kbps, it would try
harder for speech (SILK) mode, or hybrid if there was any available
bandwidth, but if you provide an overkill bitbudget opusenc assumes you
want to use it and will reproduce the signal AND the noise in the best way
possible, which is CELT with as much audio bandwidth as it can afford.

You can find the explanations of all the CTLs here:
https://www.opus-codec.org/docs/html_api/group__encoderctls.html My
understanding is that they're not exposed because using any of them can be
significantly detrimental to quality, so there's an intentional but not
insurmountable barrier to learning about and using them for your special

On Thu, Oct 31, 2019 at 12:58 AM Ulrich Windl <
Ulrich.Windl at rz.uni-regensburg.de> wrote:

> Hi!
> Useful advice, thanks! Actually I had been using foobar2000 to recode,
> because it just makes it so easy to convert multiple files while keeping
> the metadata (I confess, I'm a "tagger"). But it's easy to miss some
> encoder option when being presented some default suggestions in a dialog
> form...
> Apart form that I always had the impression that Opus could be quite smart
> detecting what the input material is like, especially when I request such a
> low bitrate, it "could at least TRY speech".
> Can you explain the effect of --set-ctl-int a bit more than the manual
> does?:
> --set-ctl-int x=y
>     Pass the encoder control x with value y (advanced). Preface with s: to
> direct the ctl to multistream s
>     This may be used multiple times
> Regards,
> Ulrich
> >>> Mathias Buhr <napcode at apparatus.de> schrieb am 30.10.2019 um 14:32 in
> Nachricht
> <e7036001-c147-c4d0-550c-330331b76f5c at apparatus.de>:
> > Hi Ulrich,
> >
> > I assume you've been using opusenc to encode the files. If that is the
> > case you can try giving the encoder some more hints about your files:
> >
> > opusenc --speech --set-ctl-int 4008=1103 ...
> >
> > The latter should tell the encoder that the signal bandwidth is 8kHz
> > (OPUS_SET_BANDWIDTH). See opus_defines.h for all valid numbers. You can
> > also experiment with the complexity settings.
> >
> > -Mathias
> >
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