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Topic: mono track not the same in each channel of headphones (Read 485 times) previous topic - next topic
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mono track not the same in each channel of headphones

This is too weird for any explanation I can come up with. Has it ever happened to anyone else? This isn’t a joke although I could see myself thinking otherwise if I weren’t experiencing it. Are there any ideas on how it could be happening or other ways to investigate it?

I encoded an audiobook as mp3, as I have many others (sourced from tapes and CDs), My result is a mono file since virtually all audiobooks are mono, aside, sometimes, from introductory music. Playback is on a Sansa ClipPlus, which I’ve been using for years.

Suddenly yesterday, track 10 of the book is producing a high level shuddering sound in the right side ear piece only (from a mono file!). I can near no trace of the actual recording on that side. This occurs from second 1 through the end of the ~13 minute track.

Repeatedly switching to the previous track, and the following track, and this track, I find the other tracks play normally, but this track continues to do its strangeness. I tried a different earbud set – same result. I have since moved on through several more tracks to continue the story; all are normal so far. Today I went back to track 10. It still does its right side shudder.

I plugged the player into my computer via USB and played several tracks via foobar2000. The track properties confirms a single channel. There is no strangeness, no noise, playing from this track, or any others, over USB and foobar2000.

I went to my USB backup hard drive. Again, using foobar2000, playback is proper.



MOD edit: Title (mno > mono)

Re: mno track not the same in each channel of headphones

Reply #1
Problem with headphones cable (short circuit/crosstalk)? Causing phase/pumping issues in certain circumstances?
Do your headophones have volume knob?

Re: mono track not the same in each channel of headphones

Reply #2
Different headphones give same results on that track -- when played through the ClipPlus electronics.
That track does not produce the noise when played through foobar2000

All other tracks are normal through all headphones.

Re: mono track not the same in each channel of headphones

Reply #3
Maybe decode it in foobar, then re-encode and see if it goes away?
John
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My compiles and utilities are at http://www.rarewares.org/

Re: mono track not the same in each channel of headphones

Reply #4
Some corruption of file when transferring to ClipPlus? Try to copy it again.

Re: mono track not the same in each channel of headphones

Reply #5
Well if it happens on ClipPlus' headphones output only I'd say it's something with electrics of the output. I had many funky problems when headphones cable was damaged or volume knob dirty - crosstalk, balance problems, etc etc. Might be interesting to take a peek at recorded waveform...

Re: mono track not the same in each channel of headphones

Reply #6
I did a number of things but none of them offered a clue as to how a mono file can produce different results in the two output channels. I don’t know how to look at the mp3, other than the displayed properties, to see if it really is mono but it was supposed to be created from wav as mono and it decodes back to wav as mono.

1) Copied the file to a new folder on the Sansa.
It still plays the same – right channel is screwed.

2) Copied from Sansa to computer hard drive, then from hard drive to new folder on the Sansa.
It still plays the same – right channel is screwed.
It plays fine on the computer.

3) Decoded computer resident file to wav then re-encoded to mp3. Copied to new folder on the Sansa.
New file plays fine on the Sansa.

4) Split the original mp3 on the computer (see 2 above). Copied resulting files to the Sansa.
New files play fine on the Sansa.

It seems to me there must be some information in the file that tells the system to do something different to the two channels. How did such information get into this file but not the other 74 files of the audiobook?

Is there some other possible mechanism?


      

Re: mono track not the same in each channel of headphones

Reply #7
You might connect ClipPlus' output to line in and record it, plus cut first 30s of the file with mp3DirectCut and upload.

Re: mono track not the same in each channel of headphones

Reply #8
Strange indeed. What firmware is the Clip+ running? Rockbox or stock FW? Based on what you've tried, the implication is that something in the file, presumably in the headers or metadata, is confusing either the player's DAC or its firmware, although I'm not expert enough to suggest what or how. Have you looked at the problem file as-is in Audacity or some such?

If you have Rockbox, try playing with stock FW then Rockbox to see if any difference is found. If you can cut a sample of the file and retain the problem, post it on here. There will be members with the Clip+ (myself included) who could try it on ours.

 

Re: mono track not the same in each channel of headphones

Reply #9
I’ve been involved with more pressing considerations than a peculiar mp3 file the past week plus but haven’t completely forgotten it.

The player is using the Sansa OS, no rockbox.

The file is mono, the player’s output is two channel. The left channel output sounds completely normal, the right channel output sounds, to me, like a square wave alternating between some very high value and a very low value about three times per second. Copying the file to the computer hard drive, renaming it, and copying that to a new folder on the Sansa preserves the strangeness but any change to the file content removes it. I don’t see how it could be something in the digital data. The file control information seems like a much more like suspect.

Decoding to wav and looking at the result in CoolEdit 2000, it looks, and sounds, quite normal in both wav and spectral views.

While I could record the output onto the computer, I don’t see how it would be an accurate reproduction of whatever causes this strangeness. It would be two separate, independent signals that are very different from each other and from the original.

Re: mono track not the same in each channel of headphones

Reply #10
Quote
It seems to me there must be some information in the file that tells the system to do something different to the two channels.
I'd guess the MP3 file has some slight corruption that doesn't affect most MP3 decoders.   Every frame in an MP3 file has a frame header with a field for mono/stereo/joint stereo/dual mono and maybe some frames have that data corrupted, and maybe that's not all..    You'll probably never know why it happened.  

You might try comparing the good & bad MP3 with MP3 Diags to see if it finds a problem or a difference.

Re: mono track not the same in each channel of headphones

Reply #11
My guess:
Incorrect decoding that results in buffer overflow, and as a result very strange things can happen.

 
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