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LAME joint stereo causes obvious difference: R channel is quiet/absent, [due to bad settings/was “Joint Stereo with Lame - strange behaviour”]
Tokoloko
post May 6 2012, 11:59
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Hello,
nomally I do my MP3 encoding with Lame using the Joint Stereo option. What I have learned so far is that there shouldn't be a big difference in sound quality between joint stereo and normal stereo (beside from what audiophile geeks think about the topic).
Now I notice that in my MP3's there is a easyly perceptible difference between joint stereo and normal stereo: It seems that the right channel is not really present (it sounds very far away and damp, but this could be a left-over from the left channel), and the left channel sounds loud as normal but in the middle and not left. You can download a wav and corresponding mp3 file (to hear what I mean) from here: http://dl.dropbox.com/u/18990880/JointStereoTest.zip (6MB)
This really surprises me, as it's really a big quality reduction of joint stereo. So, up to now, I think that I am doing something wrong in the encoding, but I did a lot of tweaking and nothing did change this effect.

Maybe someone is able to help me in this subject...

Thorsten

This post has been edited by Tokoloko: May 6 2012, 12:46
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mjb2006
post May 6 2012, 12:24
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Just going by your description, it sounds like mid-side stereo frames are being decoded as if they are simple stereo.
The left channel is the mid (L + R, i.e. the 'sum') and the right channel is the side (L - R, i.e. the 'difference').

The .zip you pointed to seems to be corrupt.

What version of LAME are you using and where did you get it?
And what are you using to play the MP3?

This post has been edited by mjb2006: May 6 2012, 12:25
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psycho
post May 6 2012, 12:27
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The file you linked to is broken.

Joint stereo shouldn't produce such behavior as you describe. At least not Mid-Side version of it. But Inensity-Stereo version of it only applies to very low bitrates, so I don't think that's your case, or is it? What's your target bitrare?


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Tokoloko
post May 6 2012, 12:50
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Ooops, it seems that my provider doesn't allow file sizes of 6MB, so I moved it to a different location. I corrected the link in the original posting.

I am using CDex to encode. Lame is version 3.99 and bitrates are between 48kpbs and 160 kbps, with VBR Method VBR-MTRH. The effect is the same whereever I play it (VLC, Audacity, MP3 player...)
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psycho
post May 6 2012, 13:00
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Yes, the link works now... You are getting a very strange output. Your mp3 file is MPEG 2 Layer III @ 22050 Hz... What settings are you using for LAME? Your resulting mp3 should be MPEG 1 Layer III @ 44100 Hz.


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Tokoloko
post May 6 2012, 13:06
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Wow, that's it...
In the settings there is a version field which I set to MPEG II.5 (assuming that higher versions are more modern and appropriate ;-) ). I set it to MPEG I and now the resulting mp3 sounds like expected!
Strange, I was nearly sure that I tried this setting, too...

But, anyway, thanks a lot for the help!
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psycho
post May 6 2012, 13:24
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I'm glad I could help. smile.gif

Yeah, MPEG-1, MPEG-2, MPEG-2.5 can confuse you if you don't know what's it all about. But in this case a higher number doesn't mean better encoder, because MPEG group was working to achieve a good format for broadcast and not for digital storage as was the case with MPEG-1.

You can also read more about MP3 here. smile.gif


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mjb2006
post May 6 2012, 14:13
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LAME gives you a lot of knobs to play with, but you really need very few of them. It's tempting to think you can research them all and use non-default settings and get better quality, but consensus here is that it's not that easy, and that the defaults are often exactly what you want. http://lame.cvs.sourceforge.net/viewvc/lam...html/usage.html
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