Possible sound quality problem with OGG vorbis playback

[Rockmenot]

Hello,
I am using Rockbox r16308 on a SanDisk Sansa e250 player.
When I play OGG Vorbis files, I often hear a cracking noise on the left channel. The strength of the annoying cracking sound depends on the audio file I am playing, and changes from time to time.
I suspected my hearpohones, but if I test the earphones on my computer, there is no problem.
Moreover, with MP3s, this problem does not appear.
I am now suspecting that when I play OGG files, the Rockbox firmware decodes the file to PCM, and reencodes it to MP3 in order to send it to the chip's ADC which decodes it back to PCM, and analog. Such a constraint could be caused by the Sansa's chipset not accepting anything other than MP3 or WMA. If this truly happens, this would be rather bad, because OGG and MP3 do not eliminate the same information when encoding. This would explain sound quality problems. In this case, this should be clearly explained on the Web page giving the list of supported file formats.

Note: I had to use a generic login/password coming from Bugmenot to send this message. E-mail address validation seems not work with addresses having multiple dots.

[EricBuist]

Registration finally worked.
I forgot to mention in my previous post that no problem appears for the right channel. I tried to switch the player to Mono, and still got the cracking sound in the left channel. This really sounds like an earphone problems, but it does not happen with my computer, and with MP3s.
I know there is nothing we can do for it, but I would like to know if OGG files are converted to MP3 internally before they are played back. If that happens, I will gradually reencode my CDs to MP3, and never ever reuse OGG Vorbis since it only causes extra work. I hope I will not have to do this, really.

[nls]

OGG files are certainly _not_ converted to mp3 when played back. The dacs in all rockbox supported players except the archos models can only handle PCM.

As to the cause of your problem. Which dsp settings have you enabled? does it happen if you disable them, how about with completely reset settings?
Does it happen with all OGG files you have?

[bertrik]

I've heard a very similar problem, on my sansa e260. Certain mp3's and wav's sound distorted on rockbox while they sound clean on a PC and on the original firmware.

A quick hack for this problem is to enable the equalizer, configure it for flat response and apply some "pre-cut" (say -5 dB).

[EricBuist]

Equalizer, and replain&gain are turned off. I only added a +5db bass, but if I set the bass to 0db, I have the same problem.
It happens for many but not all of my OGGs. I used GRip, and more recently Sound Juicer to produce these OGGs from original audio CDs.
I will try to add a cut-off with the equalizer.

[saratoga]

Distortion is pretty normal if you're not using replaygain.  What happens if you scan your file with replaygain in foobar or similar program, and then enable replaygain in rockbox?

[TexasRockbox]

The one pair of headphones work, how about the headphone jack of the Sansa?  I indicate this becaase of the consisentcy of the problem in the left channel.  Maybe the headphone plug moistened *lightly* with alcohol and the plug rotated some can clean the jack.

Just to be certain, has the player been reset to default values?

[saratoga]

I don't know, and I have simply no ways to know, because foobar and replaygain are not installed on my computer, and sudo apt-get install foobar and sudo apt-get install replaygain does not do anything in Ubuntu.

Try google.

I am extremely tired of this download/compile/make install tedious process, and I have no intention to re-encode every of my audio file to play it with my MP3 player.

Reencoding likely wouldn't help anyway, unless you were ripping to a lossless format.

[EricBuist]

Foobar is not a solution for me, because I am using Linux.
The scanning utility I needed are vorbisgain and mp3gain. But I don't think normalization will solve my distorsion problem.

[Llorean]

If the precut helped, then it's likely normalization would as well, and in a more consistent manner.

[saratoga]

Foobar is not a solution for me, because I am using Linux.

Yes I know, hence my suggestion to try google.

The scanning utility I needed are vorbisgain and mp3gain. But I don't think normalization will solve my distorsion problem.

Replaygain is not just normalization, and if you are not using it, you must anticipate distortion.  You have reported distortion.  

The obvious thing to do is to try it so that the most probable causes are ruled out first.

[TexasRockbox]

Maybe try the default Rockbox theme, watch the level meters while playing a problematic .ogg file and see if the left channel is pinning/clipping?

[EricBuist]

ReplayGain seems to help, but the problem sometimes appears again.

[Llorean]

Do you have the "prevent clipping" option enabled for Replaygain in Rockbox?

[Gregory]

I think i have experienced the same thing before.  To me the clipping would only occur at the loudest parts of a song (understandably).  By enabling the eq and only setting the pre-cut to around -2db would fix the problem.