[vorbis-dev] high frequencies response

[Frank Grotelueschen]

David K. Gasaway wrote:

>I'd better not try to explain myself, or I'd likely come off sounding like 
>a goof. :)   Check out these:
>    http://www.xiph.org/archives/vorbis/200202/0283.html
>    http://www.xiph.org/archives/vorbis/200209/0026.html
>    http://www.xiph.org/ogg/vorbis/doc/stereo.html
>AFAIK, this problem should not be observed above -q 6 in 1.0, where 
>lossless stereo coupling takes effect.

Thanks for info..
On the other hand, with quality below this limit lossy stereo encoding is
used. I think, this mode needs more tuning. But even quality 6, high
frequencies response is a little bit increased.

To check, if this problem is related to L/R- differences, i have made another
set of test-files. I have mixed both channel with 50% each other, so both
channels are identical (mono-content in a stereo wave-file).

http://home.t-online.de/home/520022073876/highfreq(left=right).zip
The length is 1,7MB.

For my ears, the result is the same as the stereo-files.

Compared to other encoders, only ogg will increase the high frequencies
response. MP3 (Lame, FHG), WMA, MP3pro etc. don't have this problem
at bitrates round 128kbps. They all sounds flat and very similar.
Only ogg fails.
I have participated in the c't listening test. As i testet the 128kbps
files, i have ranked one file to the lowest quality, because of too much
high frequencies response. All other files sounds very similar. As i
got the results from c't, i was very suprised, that the bad file was
the ogg-file. I supposed, this file was the MP3pro or something else,
but i was wrong..

With this results, i think, it gives no profit to change from mp3(lame)
to ogg. It is better to encode with lame and get bitrates round 192kbps.
Since a long time i'am using lame 3.87 with parameters "-mj -V1 -b128 -F".
For my ears, it sounds very ok with no audible artefacts and the frequencies
response is flat.
Ogg with at least quality 6 produces files with near the same filesize as
lame (seetings above) or higher. So, there is no need to change to ogg.

Frank

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