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Flaws in recent Opus codec?
post Oct 13 2012, 11:53
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Joined: 13-October 12
From: Germany
Member No.: 103833

Hi everybody,

this is my first post here, even if i read this forum for a quite long time already.

Recently i did some testing on the Opus codec an found a strange behaviour.
I encoded a file with the official 0.1.5 binaries and had a look the frequency response.
Knowing that judging quality with this is useless, i discovered a ~1000Hz /-3dB drop
around 16 kHz which is not present e.g. in Ogg encoded files.

This lead me to encode/decode a linear sweep for comparison and this finally showed
a really messed up response for the Opus encoded sweep in the HF region.
I am not quite sure if it is encoder or decoder related.
For decoding i used the official opusdec and the foobar built-in one.

Opus music sample:

Oggvorbis music sample:

Opus linear sweep:

Oggvorbis linear sweep:

What do you think? Could someone try to replicate or has this been
noticed already?

Thank you.
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post Jan 25 2013, 23:35
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Joined: 15-February 05
Member No.: 19848

145dBSPL, romor: Do your spectrograms show the mono downmix of a stereo Opus file? If so, are the graphs for only one of the stereo channels alright?

Maybe I recognise the phenomenon.
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