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Very weird MP3 quality tester

post #1 of 7
8/20/07 at 4:48am
Thread Starter 
I built a simple CMoy amp a while back, and never actually soldered everything together. So tonight I plugged it in, and one of the terminals going to the headphone jack came loose, and the "center" channel was knocked out, sort of like if you don't plug the jack all the way in. However, I noticed something odd. When I played an mp3 at 128kbps, the artifacting was almost the only thing you could hear. 192kbps, when played normally, sounds pretty close or the same as the CD, or at least to me it does. However, with the jack messed up, I could still hear some artifacting. When compared to the same song at 320kbps or .wav, there was no artifacting at all. To me, though, connected properly, they sounded the same. Just thought it was interesting, and could be a way to tell if your music is encoded at high quality or not.
Edit: It also works just not plugging the jack in all the way too.
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post #2 of 7
8/20/07 at 5:28am
I'm guessing that you're shorting the left or right channels, or using the right channel as a ground for the left, or something such. You'd probably get the "karaoke effect" that way.

It's interesting, and does give hints as to how MP3 does its magic. But of course you don't listen to MP3s like that (most of the time). The best way to evaluate MP3 compression is the same way you'd usually listen to it: normally
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post #3 of 7
8/20/07 at 9:06am
Most low bitrate mp3's are encoded with joint stereo.

It could have something to do with that..

http://en.wikipedia.org/wiki/Joint_stereo
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post #4 of 7
8/20/07 at 9:18am
Quote:
Originally Posted by Calroth View Post
It's interesting, and does give hints as to how MP3 does its magic. But of course you don't listen to MP3s like that (most of the time). The best way to evaluate MP3 compression is the same way you'd usually listen to it: normally
The best way is using a Spectral Analysis zoomed in.
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post #5 of 7
8/20/07 at 2:44pm
Thread Starter 
I know it's harder to tell the difference when the actual music is playing as it should, but now it almost feels like I need to get all 320kbps mp3s now. That joint stereo article is interesting too. That could be a reason why I'm hearing it.
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post #6 of 7
8/20/07 at 5:46pm
Mid/side stereo coding causes no degradation to the stereo. Intensity encoding hasn't been used in a long while.
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post #7 of 7
8/20/07 at 5:51pm
From the Wikipedia link above.

Quote:
Unlike intensity stereo coding, M/S coding is a special case of transform coding, and retains the audio perfectly without introducing artifacts. However, when used in conjunction with a lossy form of compression, artifacts can become apparent.
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