27 Sep
2006
27 Sep
'06
8:16 p.m.
Hi,
I was wondering if there are any tools out there to test audio
resampling quality. I am particularly interested in 44.1kHz to 48kHz
resampling due to the fact that most sound cards prefer 48kHz.
At least with up sampling (low rate to higher rate) one does not get
aliasing.
I really just want to find some algorithm that I can use to compare
44.1kHz audio signal with an 48kHz audio signal, and to see if there has
been any lose of quality during the up sample.
James
27 Sep
27 Sep
8:22 p.m.
On Wed, Sep 27, 2006 at 11:16:27 +0100, James Courtier-Dutton wrote:
Hi,
I was wondering if there are any tools out there to test audio
resampling quality. I am particularly interested in 44.1kHz to 48kHz
resampling due to the fact that most sound cards prefer 48kHz.
At least with up sampling (low rate to higher rate) one does not get
aliasing.
I really just want to find some algorithm that I can use to compare
44.1kHz audio signal with an 48kHz audio signal, and to see if there has
been any lose of quality during the up sample.
I'm not sure if it's a good technique, but to test my dithering algorithms
I took high precision FFTs of the input (sine wave IIRC) and output
signals and looked for extranous peaks. You can see the test code in the
tarball: http://plugin.org.uk/libgdither/libgdither-0.6.tar.gz
c.f. http://plugin.org.uk/libgdither/TESTING
- Steve
8:45 p.m.
Steve Harris wrote:
On Wed, Sep 27, 2006 at 11:16:27 +0100, James
Courtier-Dutton wrote:
It is not quite that easy. The buckets for FFTs at 44.1kHz rate might be
different from the buckets at 48kHz rate. Some of the buckets are the
same, but not all. I.e. the 1 Hz and the 2 Hz buckets are the same, but
the buckets above 44.1kHz might be different as the 44.1kHz rate FFT
will not have baskets above 44.1kHz.
James
Hi,
I was wondering if there are any tools out there to test audio
resampling quality. I am particularly interested in 44.1kHz to 48kHz
resampling due to the fact that most sound cards prefer 48kHz.
At least with up sampling (low rate to higher rate) one does not get
aliasing.
I really just want to find some algorithm that I can use to compare
44.1kHz audio signal with an 48kHz audio signal, and to see if there has
been any lose of quality during the up sample.
I'm not sure if it's a good technique, but to test my dithering algorithms
I took high precision FFTs of the input (sine wave IIRC) and output
signals and looked for extranous peaks. You can see the test code in the
tarball: http://plugin.org.uk/libgdither/libgdither-0.6.tar.gz
c.f. http://plugin.org.uk/libgdither/TESTING
- Steve 
8:47 p.m.
James Courtier-Dutton wrote:
Hi,
I was wondering if there are any tools out there to test audio
resampling quality. I am particularly interested in 44.1kHz to 48kHz
resampling due to the fact that most sound cards prefer 48kHz.
At least with up sampling (low rate to higher rate) one does not get
aliasing.
Err, sorry, aliasing can also be produced during up sampling; in
particular, aliasing can be created in the fs/2 to fd/2 band where
fs is the source sample rate and fd is the desitination sample rate.
I really just want to find some algorithm that I can
use to compare
44.1kHz audio signal with an 48kHz audio signal, and to see if there has
been any lose of quality during the up sample.
The Secret Rabbit Code test suite has some pretty extensive SRC
test code. YOu can get the Rabbit here:
http://www.mega-nerd.com/SRC/
and I gave a bit of a talk about this stuff at an LCA minconf in
2005. The slides are here:
http://www.mega-nerd.com/tmp/secret_rabbit_code.pdf
HTH,
Erik
--
+-----------------------------------------------------------+
Erik de Castro Lopo
+-----------------------------------------------------------+
Journalist: Microsoft CEO Steve Ballmer has finally said Linux
is the No. 1 threat to Windows. What's your response to that?
Linus : "Tag, you're it." I don't care. They've had a lot of
enemies in their time. Let them fight one enemy that
doesn't care for a change.
29 Sep
29 Sep
9:07 a.m.
Hi!
On Wed, Sep 27, 2006 at 11:16:27PM +0100, James Courtier-Dutton wrote:
I really just want to find some algorithm that I can
use to compare
44.1kHz audio signal with an 48kHz audio signal, and to see if there has
been any lose of quality during the up sample.
I am using the following for testing my resampler code:
- generate sine signal
- upsample it
- generate expected sine signal
- subtract those two
It only works if you precisely know how much delay the upsampling
introduces, but if you know this, then you can compute the exact maximum
error between these two signals and get a dB error value. If you repeat
the test for many different frequencies, you can plot how your resampler
performs at different frequencies.
Cu... Stefan
--
Stefan Westerfeld, Hamburg/Germany, http://space.twc.de/~stefan
6625
days inactive
6627
days old
linux-audio-dev@lists.linuxaudio.org
4 comments
4 participants
participants (4)
-
Erik de Castro Lopo -
James Courtier-Dutton -
Stefan Westerfeld -
Steve Harris