FS#12692 - Recording - positive clipping wraps around to negative or zero values

Attached to Project: Rockbox
Opened by dockjkox (dockjkox) - Monday, 11 June 2012, 11:51 GMT
Task Type Bugs
Category Recording
Status Unconfirmed
Assigned To No-one
Operating System Sansa AMSv2
Severity Low
Priority Normal
Reported Version Release 3.11
Due in Version Undecided
Due Date Undecided
Percent Complete 0%
Votes 0
Private No


On my Sansa Clip+ 4GB, with Rockbox v3.11.2

Recording a wav file through internal microphone. If the audio signal clips at the positive limit, bad things happen:
1) Most of the time the recorded signal wraps around to a full scale negative value, which makes it sound terrible.
2) Sometimes the recorded signal wraps around to a near zero value, which still makes it sound terrible but the distortion is not so loud

3) Clipping at the negative end of the range is as you would expect - a flat line which sounds like normal digital distortion, as you would expect

See attached picture of the recorded waveform showing each of the 3 situations described above.
This task depends upon

Comment by Michael Sevakis (MikeS) - Tuesday, 12 June 2012, 02:44 GMT
As far as I can say about AMS and its limited recording hardware is that this is a hardware issue. It's not unique to AMSv2 but the same happens with e200v1 with the AS3514.
Comment by dockjkox (dockjkox) - Tuesday, 12 June 2012, 11:48 GMT

I did see somewhere that this issue happened with some Sansa player at some time in the past, and it was fixed with a firmware update. But I can't find the link now.

I can say that this problem doesn't happen on my Clip+ with the latest Sansa Clip+ Original Firmware. The Original Firmware seems to be happy to clip pretty heavily without any apparent way to alter the sensitivity, but crucially without the wrap-around problem. See attached waveform recorded with the OF.