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Possible sound quality problem with OGG vorbis playback

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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.

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