[opus] Opus hiding lower volume instrument

[Jean-Marc Valin]

I hear nothing wrong with your file. The main difference between the
Opus file and the original is that it's quieter. That can actually be
explained by the playback gain. If you decode using opusdec, you'll see
this line:

Playback gain: -3.738281 dB

It means that whatever tool encoded your Opus file (or modified the
encoded file) decided to make it 3.7 dB quieter. Removing that gain
makes it sound close to the original. I see some tag related to an
"xACT" encoder. I suspect some kind of issue with that encoder resulted
in the gain (assuming you didn't accidentally set that yourself).

Cheers,

	Jean-Marc

On 03/03/17 03:53 PM, Lucas Clemente Vella wrote:
> When experimenting with Opus encoder, I took a random FLAC file, encoded
> it, heard it, and heard the original file. When hearing the opus encoded
> file, I thought it was a flute solo, but when I heard the original, I
> nearly fell off my chain when I noticed the piano I couldn't hear from
> the Opus in the first time. Now I know there is a piano, I can hear it
> in the Opus file, but it is much harder to notice than the original file.
> 
> I believe this is some kind of bug, because the piano is discernible
> from both Vorbis and MP3 encodes at similar bitrates (around 140 kb/s,
> which should be transparent for my not-so-good hearing in any encoding).
> What is best way for me to send the files so you can check for yourselves?
> 
> -- 
> Lucas Clemente Vella
> lvella at gmail.com <mailto:lvella at gmail.com>
> 
> 
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