Distortion Problem on Sansa

[cpchan]

"Real Audio" is just a container format and can contain one of many codecs, ranging in quality from very poor to lossless:

Ah, thanks, I didn't know RA is just a container format. I had bad experiences with some of their earlier stuff. Now this looks interesting for lossy:

raac: MPEG-4 LC-AAC (RealAudio 9)
racp: MPEG-4 HE-AAC (RealAudio 10)

Do you know how the encoder conpare to Apple's and Nero's?

Charles

[cpchan]

Well the thing is, if we're producing distorted output, then 1) It should show up on RMAA tests, and 2) We need to fix it. Can you provide more information?

I am on a trip right now. I will compare it to the lossless source when I get home on Wed. and report back.

Charles

[Llorean]

Are you using a lossless file?

[Vortex]

,the real audio codec is like an improvement of the wma codec,I had my sound library in dap as wma files,but now I converted my sansa into a rhapsody one and I converted all my files to real audio

That way you don't have any quality gain, rather the opposite.

real audio codec is like an improvement to the wma codec,but in another way as container,if you use a 128kbps encoded wma the equivalent to that file in wma is the real audio at 160kbps,almost same size.

Well, in what way would the Real Audio codec be better than wma when you have to use a higher bitrate to achieve the same quality? You don't seem to make any sense to me, sorry.

What about distortion,may someone explain me on what consists that?

It basically sounds like someone stood to close to the microphone during recording. That way, "s" sounds will be too loud and therefore distort.
The "problem" here is that those files sound play perfectly fine on the Computer/some other device but on the Sansa it distorts.

Do you know how the encoder conpare to Apple's and Nero's?

I would rather use Ogg/Vorbis than AAC (if you can).
That's because
a) Vorbis is OpenSource
b) it achieves better quality at low bitrates than AAC. That's what I have read at least (I don't have the link anymore, but it was said by some guy who conducted listening tests as well as a technical audio analysis with different codecs). The AAC tracks in some HD test videos I have downloaded from the web didn't sound too great either, but that might be the fault of mplayer's AAC decoder.

Are you using a lossless file?

No, I have encoded all my files to Vorbis on the Sansa.

[Llorean]

The exact same file plays without distortion on the PC?

Can you provide a sample clip, maybe 3 or 4 seconds that very clearly shows this problem?

[X86]

hmmmm...very weird,I test the audio files on pc and then in the dap to check distortions and/or glitches on them,and I've never noticed distortion,the distortion may become when you change between audio formats and bitrates,sometimes you need to do the process to convert to other audio format three times,but that occurs in the worst cases I have had,and as caution I test the audio files in the pc and then in the dap,to check audio file glitchesand/or distortions.

[Vortex]

Can you provide a sample clip, maybe 3 or 4 seconds that very clearly shows this problem?

I have uploaded a sample clip at Mediafire.
Even though this is just a small snipplet and not the entire song I thought that it might still be best to put up a warning: This song might cause serious mental injury!

Why did I still choose it? Well, you asked for a clip that very clearly shows the issue. Searching through the collection on my Sansa I couldn't find a better song to demonstrate this.

Anyway here it is:http://www.mediafire.com/?3mlvzw7mwhx

It's a zip archive that contains a snipplet of the original file, as well as a recording from the Sansa. I encoded both to FLAC to save space (that shouldn't be a problem since FLAC is lossless, I thought).

The recording was made using the Line-In of my Computer's soundcard (Creative Audigy2 Value).

I hope this helps...

[Llorean]

I actually meant a clip of the original file, so that I could test it on my Sansa, on other Rockbox players, and on my computer, to see if it was a decoder issue, or a hardware issue, or something strange that just happens to some people and not the rest of us.

[cpchan]

I would rather use Ogg/Vorbis than AAC (if you can).
That's because
a) Vorbis is OpenSource

You don't have to convince me. I have been using Vorbis since the beginning.   I am also on the Vorbis mailinglist and talk to Monty once in a while. I was just curious about the quality of RA's AAC encoder.

b) it achieves better quality at low bitrates than AAC.

Only if you use the AoTuV branch. A lot of the low bitrate tuning have not been folded in Xiph's official branch since Monty has been rather busy. Also, accorded to the low bitrate ABX tests on HA, it is a toss up between AoTuV Vorbis and HE-AAC.

Charles
 

[Vortex]

I actually meant a clip of the original file, so that I could test it on my Sansa, on other Rockbox players, and on my computer, to see if it was a decoder issue, or a hardware issue, or something strange that just happens to some people and not the rest of us.

A small clip of the original file is included in the zip archive I posted. It was re-encoded to FLAC though, but since FLAC is lossless there shouldn't be any difference to the source Vorbis file.

[saratoga]

Can you provide a sample clip, maybe 3 or 4 seconds that very clearly shows this problem?

I have uploaded a sample clip at Mediafire.
Even though this is just a small snipplet and not the entire song I thought that it might still be best to put up a warning: This song might cause serious mental injury!

Why did I still choose it? Well, you asked for a clip that very clearly shows the issue. Searching through the collection on my Sansa I couldn't find a better song to demonstrate this.

Anyway here it is:http://www.mediafire.com/?3mlvzw7mwhx

It's a zip archive that contains a snipplet of the original file, as well as a recording from the Sansa. I encoded both to FLAC to save space (that shouldn't be a problem since FLAC is lossless, I thought).

The recording was made using the Line-In of my Computer's soundcard (Creative Audigy2 Value).

I hope this helps...

That clip is peak normalized to 0 dB, so if it is encoded into any lossy format it will distort to some extent.  You must use replaygain with it.

[Llorean]

If the problem is in the vorbis decoder, rather than in the hardware drivers,  it matters quite a bit that you've transcoded it...

[Vortex]

If the problem is in the vorbis decoder, rather than in the hardware drivers,  it matters quite a bit that you've transcoded it...

The distortion occurs whether I play the transcoded FLAC or the Vorbis file, so I doubt it's the vorbis decoder's fault.

Nevertheless I have uploaded a non-transcoded snipplet (it was split with mp3splt, without re-encoding the file).
http://www.mediafire.com/?fsztcp8m92h

That clip is peak normalized to 0 dB, so if it is encoded into any lossy format it will distort to some extent.  You must use replaygain with it.

Can you explain that a bit, please? I don't know what you mean with "peak normalized" and I don't understand why I "must use replaygain". I don't have to use replaygain on my Computer to play the file distortion-free after all.

[Chronon]

I think "peak normalized to 0 dB" means that the peak sample for the clip is scaled to correspond to a value of 0 dB.  I have some theories as to the reasons that transcoding to lossy formats would cause clipping, but I'll let saratoga answer that as this is much more his area of expertise than mine.

[saratoga]

Can you explain that a bit, please? I don't know what you mean with "peak normalized" and I don't understand why I "must use replaygain". I don't have to use replaygain on my Computer to play the file distortion-free after all.

It means if you make the file even one interval louder, it will distort.  Any lossy codec will add noise, which will push you into distortion.

This may not be what you're hearing, but you need to account for it first.