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changing bit rate in iTunes

post #1 of 5
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Is it possible to change the bit rate of songs already in iTunes? I have a bunch at 300+ and am looking to save room by taking them down around 160 - how do i do it?:confused:
post #2 of 5
Although it is possible to take MP3s encoded at a high bitrate and encode them at a lower one, doing so will compound the quality loss that is inherent in any lossy audio compression.

The best thing to do is re-encde your collection from the original CD source. If space is a concern, you should check out LAME instead of iTunes' built-in encoder, since its variable bit rate encoder tends to produce the best compromise between quality and file size. AAC (built into QuickTime 6) and Ogg Vorbis are good alternatives as well, if you don't mind different formats.
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post #3 of 5
Quote:
Originally posted by son of Gib
Is it possible to change the bit rate of songs already in iTunes? I have a bunch at 300+ and am looking to save room by taking them down around 160 - how do i do it?:confused:

Advanced -> Convert Selection to XXX

You have to choose between WAV, AIFF and MP3 in preferences.

If you're going from 300+ to 160 and it's mp3 -> mp3 then you won't notice as much audio degredation as you woud from a lower bitrate and changing codecs. In fact I doubt you'd notice it at all.

To make sure you get the best bang per bit make sure to turn on VBR and joint-stereo.

You can probably reduce the bitrate selector to as low as it goes as it is an *absolute minimum* in Variable Bit Rate encoding and it needs to go low when it can so that it can go high when it needs to.

I don't use iTunes to encode but my lame-encoded mp3s dip to 32kbps during moments of near silence.

I don't know which iTunes quality setting gives you 160kbps on average but I'm guessing medium will be the one. You can always experiment, remember thrash metal will be higher than average and classical lower, as they are harder and easier to encode respectively.
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post #4 of 5
i agree with "stupider...likeafox."

the only thing i'd add is that the VBR implementation in itunes is horrible and will produce low avg bitrates with terrible sound if you set the min bitrate too low. encoding with LAME is much better.

if you want to stick with itunes, either use VBR but don't set the min bitrate too low, or just use CBR at 160 or whatever you want.

BTW, how do you know that your lame-encoded songs dip to 32kbps during moments of silenc? what software do you use that allows you to see the actual bitrate used at each point in time throughout the song?
post #5 of 5
If you use the command line version of lame from fink it creates a little bar graph showing data rates and what the ratio of stereo to joint-stereo is.

I can't find a screenshot of this on a unix machine but here's a similar one on the windows command line:


Also some mp3 player apps will show a constantly changing bitrate though I can't think of one off-hand.
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