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Resizing iTunes Library by lowering bit rate mp3's
Spefferonie
post Dec 16 2013, 17:25
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To resize my iTunes Library I'm thinking of lowering the quality of my mp3's, because the bit rate varies from 96 to 320 kbps. Only the mp3's I converted myself after ripping my album collection to flac will remain untouched. Those files were done by my customised settings and I still have a lossless source. I can reduce the size of my library sufficiently by converting all other songs above 192 kbps to that amount at a constant bit rate, because I don't believe the loss in audio quality will make so much of a difference. So, should I just do it?
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pdq
post Dec 16 2013, 17:38
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No you should not do it (just my opinion).

However, if you do then why limit your quality by using encoding to constant bitrate. You would be much better to encode to variable bitrate, after testing for yourself which quality setting gives you the quality that you want.

Most people find a quality setting of -V 4 or -V 5 to be nearly transparent to them (although you may need something somewhat better than that to overcome the effects of reencoding).
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Spefferonie
post Dec 16 2013, 17:46
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QUOTE (pdq @ Dec 16 2013, 17:38) *
No you should not do it (just my opinion).

However, if you do then why limit your quality by using encoding to constant bitrate. You would be much better to encode to variable bitrate, after testing for yourself which quality setting gives you the quality that you want.

Most people find a quality setting of -V 4 or -V 5 to be nearly transparent to them (although you may need something somewhat better than that to overcome the effects of reencoding).


Thanks for sharing your opinion. You are right when you say that if I would do it, VBR settings are preferable. I will test it on a couple of songs with a minimum setting of 160 kbps at a high overall quality and listen to them on a good audio system to check if I notice any difference.
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DonP
post Dec 16 2013, 17:56
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QUOTE (Spefferonie @ Dec 16 2013, 11:46) *
Thanks for sharing your opinion. You are right when you say that if I would do it, VBR settings are preferable. I will test it on a couple of songs with a minimum setting of 160 kbps at a high overall quality and listen to them on a good audio system to check if I notice any difference.


Any particular reason you wouldn't just go with a standard setting of -V <something>? Is there something magic about a minimum 160 kb/s that the developers didn't know about?
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pdq
post Dec 16 2013, 18:22
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QUOTE (Spefferonie @ Dec 16 2013, 11:46) *
Thanks for sharing your opinion. You are right when you say that if I would do it, VBR settings are preferable. I will test it on a couple of songs with a minimum setting of 160 kbps at a high overall quality and listen to them on a good audio system to check if I notice any difference.

This sounds as though you are using some kind of GUI interface that disguises the lame command line switches from you. If this is the case then it may present the -V quality settings as a "typical" bitrate. That is probably OK as long as you don't take this "bitrate" setting too literally. Go ahead and try various settings until you find one that you like.

However, if it also gives you options such as something like "true stereo" vs. joint stereo, ALWAYS select joint stereo.
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TomasPin
post Dec 16 2013, 19:23
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If you can, use ABX testing software to determine whether your re-encodes are transparent, as knowing beforehand which file you are listening to may lead to the much unwanted placebo effect.


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greynol
post Dec 16 2013, 19:37
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Placebo effect can run both ways. Expecting not to hear a difference can result in not hearing a difference in a sighted evaluation when a double-blind test may reveal a difference provided the listener actually makes an honest effort.


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TomasPin
post Dec 16 2013, 21:46
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Yes, that's true. You must be getting tired of correcting / clarifying my thoughts. laugh.gif


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db1989
post Dec 17 2013, 00:10
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To expand/run parallel to what DonP and pdq already posted:
QUOTE (Spefferonie @ Dec 16 2013, 11:46) *
a minimum setting of 160 kbps
In what sense? (A) VBR is targeted to quality, not bitrate, so you should not expend much mental energy thinking about the latter, and (B) literally enforcing a minimal frame size is almost certainly a bad idea that can effectively cripple the VBR model from fulfilling its reason for being.

Also, this seems to fall short of qualifying as Tech, so I moved it here

This post has been edited by db1989: Dec 17 2013, 00:12
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Makaki
post Dec 17 2013, 07:08
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QUOTE (Spefferonie @ Dec 16 2013, 12:25) *
Only the mp3's I converted myself after ripping my album collection to flac will remain untouched. Those files were done by my customised settings and I still have a lossless source ... So, should I just do it?


No, you shouldn't that's my opinion.

If anything, the ones you have a lossless source, can be re-coded as many times as you want, because you still have the lossless copy. But do you have a lossless source for those "other" MP3s?
If those MP3s are all you got, you shouldn't transcode them.

However, ABX'ing the files may be a good alternative. Because if you can't tell the difference in quality, then you've gained some space for free.

Your potential savings:
320kbps -> 256kbps: 20%
320kbps -> 192kbps: 40%
256kbps -> 192kbps: 25%
How you value those percentages vs the possible loss in quality is up to you.

This post has been edited by Makaki: Dec 17 2013, 07:09
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