Support and General Use > Recording
Strange noises when recording to mp3
Davide-NYC:
Check out the weird DC offset. I've posted screenshots from Audacity showing the start and end of the file. Maybe this have something to do with the power section? (I don't know, just throwing ideas around) JHMikeS to the rescue?
lee321987:
I get the offset with both players, and in all formats (even with the OF).
Good eye.
Would you say my description of the noise ("like a VERY low bit rate encoding") is accurate?
BTW this distortion is occurring even when the LCD is off.
dreamlayers:
It effectively is a low bitrate MP3. Sure, the frame size is 160 kbps, but if you look at the file in a hex editor you'll see most bytes are FF. When I used mp3packer on it to losslessly compress it, the resulting file is 38,845 bytes (packed from 571,024) and EncSpot says the average bitrate is 10 kbps!
Note that the noise is very faint. It's practically a straight line on those graphs and I need to turn up the volume to hear it. My Gmini 220 running the original firmware has the same issue. I wonder if MP3 encoders are meant to accurately encode low volumes. Maybe the psychoacoustic model decides it's mostly inaudible, and it devotes very few bits to it, which results in what you see and hear here.
No idea about that DC offset. I've never seen an MP3 with a DC offset.
lee321987:
Ok, I just did two more recordings - a 16 kbps, and a 160 kbps, and after using mp3Packer EncSpot reports 14 and 15 kbps (respectively). Also I compressed a 160 kbps form my c240 (the "good" one), and it turned out 134 kbps.
So the c250 is accepting my choice of bit rate, but only encoding 16 kbps worth of data...?
Both of my players are using the same OF and the same version of Rockbox.
What could cause this?
Llorean:
Did you say you experience similar problems in the OF earlier?
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