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Transcoding MP3s from a higher bitrate to a lower one
spikeh
post Jun 10 2006, 16:17
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I'd like to transcode some high bitrate MP3s, which are usually -V 2 --vbr-new but there are a few even higher ones among them. Can I transcode them to a lower bitrate VBR (-V 5) for portable listening without suffering TWO quality losses, one from the reduction in bitrate and the other from transcoding? Is it alright transcoding from CBR to VBR, providing the CBR has a higher bitrate than the VBR?
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krmathis
post Jun 10 2006, 16:27
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QUOTE (spikeh @ Jun 10 2006, 17:17) *
I'd like to transcode some high bitrate MP3s, which are usually -V 2 --vbr-new but there are a few even higher ones among them. Can I transcode them to a lower bitrate VBR (-V 5) for portable listening without suffering TWO quality losses, one from the reduction in bitrate and the other from transcoding?
No, you can not.
You lost bits of information when you encoded to MP3 the first time, and you will loose additional information when you use transcode this file to a new lossy one.
QUOTE
Is it alright transcoding from CBR to VBR, providing the CBR has a higher bitrate than the VBR?
That is totally up to you to decide. If the decreased filesize are worth the additional decrease in sound quality.

In both cases you better use a lossless source, like the original CD.

This post has been edited by krmathis: Jun 10 2006, 16:28
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kjoonlee
post Jun 10 2006, 16:27
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Transcoding causes quality loss even if the resulting file is larger than the source.

Whether it's noticeable depends on several factors.


--------------------
http://blacksun.ivyro.net/vorbis/vorbisfaq.htm
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guruboolez
post Jun 10 2006, 16:31
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From my small experience I'd say to NOT DO THAT. The amount of extra-distortion was surprisingly high when I converted from LAME to LAME the same file. But try yourself. Quality of lossy encoding highly depends on the listener's abilities to catch specific artefacts.
Anyway, don't expect to maintain the same quality. Better take the original material as source for a new encoding purpose.
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Supacon
post Jun 10 2006, 17:24
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It's not a good option if quality is important to you. If you can, re-rip your CDs, or if that's not an option it might be better to seek out new copies on the net or whatever you need to do.

On the other hand, if you're. more concerned about reducing filesize, and you're not going to listen closely with good headphones in a low-noise environment, the quality loss could be tolerable, especially with 320 kb/s MP3s.
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AndyH-ha
post Jun 11 2006, 07:00
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I've done this with a number of audio book recordings, spoken voice only, no music. I was able to get considerably smaller files that were impossible for me to distinguish from the original encoding.

The easy thing is to take a few small samples, say 5 to 20 seconds, and do whatever you want with them. Then you have something easy to test in WinABX or one of the several other blind A/B programs.
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