Re: [Ekiga-list] Bad sound quality because of missing low passfilter

[Christian Jaeger <chrjae gmail com>]

Ok, so here is a test that should enable everyone to see whether they
are suffering from the problem or not:

Run this to see how it sounds if the low-pass filter is missing [REFERENCE]:

arecord -t raw -f dat -c 1 | bfr -m 36000 | perl -we 'while (read
STDIN, $buf, 8*6) { print substr $buf,0,8 }' |bfr -m 6000 | aplay -t
raw -f dat -r 8000 -c 1 -

Run this to see how it sounds if the low-pass filter is there (here by
using sox to implement it in software): [A]

arecord -t raw -f dat -c 1 | bfr -m 36000 | sox -t raw -r 48000 -s -2
-c 1 -  -t raw -r 8000 -   resample -ql |bfr -m 6000 | aplay -t raw -f
dat -r 8000 -c 1 -

Then check with how it sounds when relying on your sound card: [B]

arecord -t raw -f dat -r 8000 -c 1 | bfr -m 12000 | aplay -t raw -f
dat -r 8000 -c 1 -


If REFERENCE sounds like A to you, then your setup in fact seems to
implement filtering correctly. If REFERENCE sounds like B to you, then
your setup does not implement filtering (like my case).

Christian.

PS. I can't subscribe to the ALSA user mailing list, I never get the
subscription confirmation emails.