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MP3 vs AAC File Sizes?

post #1 of 5
Thread Starter 
At a given bit rate (lets say 192 Kbps), how does the file size for AAC compare with MP3 for the same song? I'm trying to work out what size HD and iPod I'd need to get my entire CD collection encoded.

Thanks,

Dave.
post #2 of 5
Quote:
Originally posted by Dave Abrey
At a given bit rate (lets say 192 Kbps), how does the file size for AAC compare with MP3 for the same song? I'm trying to work out what size HD and iPod I'd need to get my entire CD collection encoded.

at a given bit rate, file size is exactly the same. it's the number of bits per second. the size still might vary slightly with varying settings... you can rip mp3 at "variable bit rate" (VBR) which means it varies the bitrate up and down slightly according to the complexity of the music, using lower quality when the music is less complex and higher quality when it is more complex. AFAIK m4p always does this and is better at it. but the file sizes will still be very close.

the question to ask is which bitrate should you use. apple claims that m4p is basically near cd quality at 128kbs. i think it definitely sounds much better than mp3 at this bitrate, but many people have reported strange artifacts in m4p (crackling, incorrect stereo panning, et cetera), and i have heard some of these and am still investigating the issue before i go all out and re-rip my whole library. the lowest rate at which i would suggest ripping mp3s is 160, and for music like classical or jazz, 192. my whole library is ripped at around 224 mp3. (with vbr turned on... the settings are kind of confusing, and i'm still not sure if changing the bitrate setting makes any difference when using vbr... does anyone have an answer to this question?).

that said, when my g5 comes i am almost certainly going to drag my itunes library into the trash and re-rip my entire cd collection at 160 m4p (my ipod is only 5 gigs so it will be a big space savings).
post #3 of 5
I was under the impression that if you encoded both in 192kbps then they would be the same size??

People are saying that 128kbps in AAC format is about the same quality as 160kbps in MP# format. It is here that the "savings" are generated. This means the files are about 80% of the original size.

Edit: Beaten to the punch - spent too long looking for a calculator! (Yes I know my laptop has one - but without an extended keyboard I hate using it)
post #4 of 5
Quote:
Originally posted by Dave Abrey
At a given bit rate (lets say 192 Kbps), how does the file size for AAC compare with MP3 for the same song? I'm trying to work out what size HD and iPod I'd need to get my entire CD collection encoded.

Thanks,

Dave.

I'm filling up my HD (gotta use the space for something) with songs first. Then I'll decide what size iPod I need. I encode at 160 kbps AAC, and so far 1779 songs = 9.53 Gb.
When I add in some online radio recordings (Audio Hijack: 2 hours at 128 kbps MP3 = ~100 Mb per file). To maintain iPod battery life I'll probably chop each file into 30Mb chunks so the iPod can store them in RAM instead of keeping the HD spinning.

So I think I'll have to get a 40 gigger eventually.
post #5 of 5
Thread Starter 
Oops! You're right of course, at the same bit rate, the file size should be the same . I guess I should have asked something like at what rate would an AAC file be encoded to get similar sound to a 192 Kbps MP3, and thus how much smaller would the file be. I think this is the answer I was after:

Quote:
People are saying that 128kbps in AAC format is about the same quality as 160kbps in MP# format. It is here that the "savings" are generated. This means the files are about 80% of the original size.

Thanks,

Dave.
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