Support and General Use > Recording
Strange noises when recording to mp3
lee321987:
Not the noise, just the DC offset, but the WAVs made by the OF and Rockbox do not contain this noise.
dreamlayers:
So apparently the DC offset is actually present in data coming from the ADC and not from MP3 encoding. Perhaps the DC offset is a problem for the MP3 encoder?
Edit: Just out of curiosity I generated a file with faint white noise and a DC offset and then encoded it with LAME 3.97. The resulting file had irregular bass pulses (which were not present in the original) but the white noise sounded otherwise okay. I think I made my noise more intense than your noise. Go ahead, try to encode those WAV files with LAME and see how it messes them up.
lee321987:
Ok, I think you're right. Remember I said the c240 doesn't produce this noise? I just compared (with Audacity) the size of the offset on both players. On the c240's file the top of the (noise only) part of the wave form was just about at 0. The top of the (noise only) part of the c250 file's wave form was at about 0.05.
What exactly is this number (the scale just to the left of the wave form in Audacity)? Some variation of dB?
Would it even be possible to program a correction for this offset into Rockbox?
Thanks for the help guys,
Will
Davide-NYC:
--- Quote from: lee321987 on May 02, 2008, 04:58:51 AM --- Not the noise, just the DC offset, but the WAVs made by the OF and Rockbox do not contain this noise.
--- End quote ---
Since the noise is very low DB and this does not happen with WAV files I'm going to presume it is caused by the encoder. The DC offset, on the other hand, I would presume is attributable to the hardware, since it appears with both the OF and RB.
Some questions just to clarify exactly what is going on:
* Do WAV files have this DC offset as well?
* Does this offset exist on both of your C2x0 units?
* Does this offset happen when recording with Sansa E2x0 units?
Llorean:
The Rockbox MP3 encoder is, if I recall, fairly low quality. It was chosen because it's fast, rather than being tuned for quality, and should only be used if you absolutely do not have the space for higher quality file types.
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