Support and General Use > Recording
Strange noises when recording to mp3
lee321987:
I did a test, a link to my results is here. In the zip is a file called "original.wav", this is a short recording of silence made using Rockbox on my c250.
Description of the other files: The files with "RB_encoded" in their name were made on my c250 with Rockbox's "Open With... > mp3_encoder" command. The files with LAME in their name were made with Audacity using LAME 3.97. The file "offset_corrected.wav" is "original.wav" with the offset corrected by Audacity, and all mp3's with "offset_corrected" in their name were encoded from this wav.
I now have no doubt that the culprit is my c250's large DC offset.
Multiplex:
--- Quote from: lee321987 on May 13, 2008, 06:21:45 AM --- I now have no doubt that the culprit is my c250's large DC offset.
--- End quote ---
So I wonder how practical it would be to do a custom build to subtract the offset from the data comming from the ADC...
Davide-NYC:
If this noise bothers you it means you need to bite the bullet and buy a better target.
The DC offset on a recording @ 22k/16bit from a super crappy mic is not worth fretting over.
Better targets do not exhibit this behavior.
I would suggest buying an iriver h120.
If you need timestamp RTCMod it.
If you need total silence (no HD spinup) put a CFCard in it.
:)
Then again, there might be some hardware guru that can resolve this with a paperclip, some chewing gum and a piece of tinfoil. I'm not that person.
I will mention that if Rockbox keeps getting ported to crappy target with even crappier recording support (which I fully endorse, the more target supported the better) it might be a reasonable idea to try to implement an (optional) auto-DC-offset filter for recordings on targets that have the problem.
AlexP:
--- Quote from: Davide-NYC on May 23, 2008, 10:18:42 AM --- crappy target with even crappier recording support (which I fully endorse, the more target supported the better)
--- End quote ---
There really is no need for this. You may not like certain targets, but plenty of people do.
petur:
there is an MP3 encoder patch in the tracker that claims to fix stuff like DC offset.
Maybe you can try it out?
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