"Pete Cross" 1@2 wrote in message ...
Can any of you produce a clean sounding mp3 of a swept frequency test cd ?
the source has to be a commercial cd with a sweep freq track on it. I
suspect not, I played a test cd in a portable cd player with it's anti jog
feature enabled, it sounded dreadfull but music cds still sounded ok. nb
the
anti jog spins the cd twice it's normal speed and reads ahead into a
buffer
to give it time to recover if it gets jogged, it really messed up the
sweep
from 10kHz onwards.

--
Pete Cross

Pete, I can do a 20-20kHz MP3 sweep, what but rate did you want it done at?
Let me have an email address to send it to.

Note that MP3 (and MP2) use psychoacoustic masking to reduce the bit rate.
This means that the audio band is broken down into many (don't know exactly
how many) individual frequency bands, with the idea that quiet sounds in
bands adjacent to loud sounds will be masked and therefore not codec. The
many filters means that a sweep will be constantly crossing filter
boundaries dynamically, and will pretty much confuse the MPEG coder.

When there was the 199? Football World Cup in France, I sold France Telecom
a large number of automatic audio test meters so FT could test the 400+ ISDN
codecs they bought to provide audio feeds to the world's broadcasters. These
ISDN codecs were being used on MP2 at 128kbps (pretty much as DAB is in the
UK). Using spot frequencies, all tests were fine, as was audio quality
(mostly speech). but as soon as the automated sweep went through, the
frequency response had so many anomalies as to be meaningless. FT solemly
carried out the tests, failed every codec, but used them anyway....aren't
the French wonderful?........

S.