Mp3 to AAC quality loss

If it is a high quality MP3 making it ACC wont hurt, but if they 128k MP3 it will make them sound pretty bad.

It's not been proven as a fact yet but I believe people are following along with the Apple marketing machine and thinking that AAC files, while similar or better in audio quality, are naturally smaller in size. Note that I myself didn't say that, Apple's marketing machine did.

As quoted from Apple's iPod Homepage (http://www.apple.com/ipod/):

"AAC features CD-quality audio in smaller file sizes than MP3, so that even more songs fit on your iPod." If you disect this statement for what it means it makes sense; but on the surface of it 99% of the people that will buy/plan to buy an iPod will read that sentence in some manner like this:

"Oh man, it says here I can put my music onto an iPod at smaller files sizes than the mp3 files I've been using so far..."

They interpret Apple's marketing as saying AAC files are smaller in all cases and this is where the problem lies. If you didn't *get it* read that sentence again. I'll wait.

Ok, so now we discover what it really says and means. It says "AAC features CD-quality audio in smaller file sizes than MP3". That's it, right there, in black and white (depending on your font/background colors of course). CD-quality audio in smaller filesizes - meaning the way that AAC works will create similar or better sounding files but in smaller sizes - but not at the same bitrate, of course. AAC is more efficient in that respect; you get more for less, so to speak. An AAC file at 128Kbps is widely regarded as "near CD quality" or even "CD quality" while an MP3 would have to be encoded at at least 192Kbps to considered "CD quality" - even using LAME which is, once again, widely regarded as the best MP3 encoder available.

Since it's a constant bitrate it doesn't matter if it's MP3 or AAC, similar bitrates offer similar filesizes. AAC and MP3 are similar in size at the same bitrate. If you encode a WAV file to a 128Kbps MP3 file and it turns out to be around 5MB or so in size, the same WAV encoded to 128Kbps AAC will probably be 4.7 to 5MB in size. Same bitrates, similar filesizes. This isn't rocket science so don't chew me out due to inexact numbers down to the 13th digit past the decimal point.

The point is that while AAC files generally tend to be somewhat smaller, you're not going to get an AAC file that's half the size of a similar MP3 file (per given bitrate).

I was thinking at one time when I get an iPod (soon to get a 30GB 3G model) that I'd actually go through the process of transcoding the 50 CDs of mp3 files I've made over the past 3 years or so. All of them are LAME 3.9x --alt-preset standard stuff but at this point I decided to say, "Screw it" and I'll just import them into iTunes and enjoy them as they are.

The quality is important up to a point but I have a firm belief that sometimes people hear what they want to hear. Oh boy, there's a real shocker, eh?

So in the end it's personal choice after all - what sounds good to you and your ears is all the really matters. If I were asked to make recommendations at this point here's what I'd suggest:

If you have any MP3 files that you encoded before buying an iPod leave them as MP3 files. You do realize the iPod plays MP3 files, right? However, if you have any new CD content/WAV files/etc that have NOT been encoded yet I'd go for AAC all the way. At least that's what I plan to do with my iPod; I've already started converting all newly acquired content to AAC format and I've stopped encoding anything in MP3 format whatsoever.

Again, that's just how I do it.

:D

br0adband

The thing is that those kinds of comparisons have been done ad nauseum all over the place. The most respected site (in my humble opinion, of course) is:

HydrogenAudio.org (http://www.hydrogenaudio.org)

Some of the most awesome information regarding audio compression technologies take place there. Some of the people directly responsible for coding LAME and AAC hang out there and post on a regular basis: Dibrom of LAME fame and Ivan Dimkovic (sp?) of AAC fame.

As far as MP3 rolling off the high end... well that's debatable. It all comes down to the encoder and LAME can handle it.

Check it out sometime if you can (if you didn't already know about it, that is).

br0adband