transcoding mp3s? To aac?

September 22, 2006 11:39 PM

I just bought a new 8gb ipod nano. I've got about 11gbs I want to shove onto the player. So, I'm thinking about stepping down the bit rates of my mp3s. How should I do it?

Most of my music is 128kbs mp3. My newer rips are higher, but that's a small minority of the collection.

I'm keeping all my music in it's original form on my computer, so I'm not worried about losing some quality. I usually listen on mid-range earbuds (not the white ipod ones) in a fairly noisy environment. I'm not an audiophile, I don't think my ear is very sensitive.

So, I checked, and at 80kbs I could fit it all on my nano. But should I transcode to aac? Will that sound better than an 80kbps mp3, considering the source was an mp3?

Will I never notice with my non-expert ear, either way?

posted by bluejayk to Technology (21 answers total)

According to some sources, AAC sounds better than MP3 at the same bitrate. Your non-expert ear may develop into a semi-expert ear. Why don't you try it out first and see if it works for you?
posted by roomwithaview at 11:51 PM on September 22, 2006

Not the answer you're looking for, but I'd hesitate to go lower than 128 - at some point you may want to use nicer speakers in the car or at a party or something. I know that in my muisic collection, I could easily trim a couple of gigs by saying: "Nah, I really don't listen to that much". Do I really need to tote xmas music around all year? Or that podcast that I'll probably never listen to anyway?
posted by chrisamiller at 12:01 AM on September 23, 2006

As long as you're keeping the originals, what have you got to lose? Transcode them, see if you can live with the lower quality. If you can't, dump them and just put a subset of your songs on the iPod.

But if you are keeping them, how are you going to juggle the multiple versions of the files? I guess iTunes will happily list two versions of the same file, but that's going to get annoying for you.

What would be useful is some smart way of swapping iTunes preference folders, or using user profiles to keep two distinct collections at two different bitrates.
posted by AmbroseChapel at 12:07 AM on September 23, 2006

Don't transcode, there's always going to be serious quality loss there. Instead, re-encode our source to 80kbps.
posted by jedrek at 12:18 AM on September 23, 2006

Transcoding to AAC ought to sound a bit better than re-compressing to MP3 again. I'd probably do desktop search for all *.mp3 files, sort it by size, and just compress the largest files.
posted by unmake at 12:54 AM on September 23, 2006

What would be useful is some smart way of swapping iTunes preference folders

The new iTunes 7 supports multiple libraries. Since the implementation only lets you use one of them at a time, it seemed kind of useless to me. But this would be a perfect use for it. Duplicate your library; downsample; switch to the downsampled library for a while. If the experiment proves a bust, no harm done. Or if all's good, you can use the files without having to look at two of everything.
posted by nakedcodemonkey at 1:08 AM on September 23, 2006

I wouldn't go below 128kbs. That's bad enough. With 11 gbs of mp3s you can afford to thin some out to be rotated back in later. You have tens of thousands of songs, right?
posted by wsg at 1:56 AM on September 23, 2006

when I had a tiny MP3 player I used this program to shrink them:

http://www.skyshape.com/mp3resizer.html

worked great and I never noticed a difference until I got an iPod and closed cell headphones

reg
posted by legotech at 2:21 AM on September 23, 2006

I don't think you should encode music below 128, let alone transcode it below that. I encode higher than that myself, but most people notice degradation on decent speakers or headphones if the bitrate is below 128. If you transcode to 80 from a higher bitrate, it's going to be even worse.

Transcoding to AAC ought to sound a bit better than re-compressing to MP3 again.

Probably not. You want to avoid transcoding from a lossy format, like mp3, to another one, like aac. That said, you should use variable bitrate encoding whenever possible. It gives you the best quality for the fewest bits. iTunes will let you use this for aac files. The LAME encoder will let you use it for mp3 files (google it, if you're interested). Use it if you can.

Anyway, you can always try these suggestions for yourself and use your own ears to judge. Make sure to test different genres of music on all of the speakers and headphones you'll be using.
posted by smorange at 3:19 AM on September 23, 2006

my favorite part about my nano is getting my collection (80+ gig) pared down the bare essentials that will fit on it.
posted by sophist at 3:39 AM on September 23, 2006

Response by poster: Thanks for the suggestions.. to reiterate, I will not be compressing or transcoding my originals, they will be kept safe and sound.

I'm curious why transcoding is so bad? Are the algorithms so different that they take away different parts of the music so that when you run them twice, you have twice as much stuff taken away?

I ran a sample test, but I'm not sure what to look for. I tried one techno song, and one Radiohead song, choosing those because I figured they had the widest range of 'weird' sounds that would be easy to notice changes in.

Well, maybe it's cause I just ran it through my notebook sound card, but it all sounded the same, transcoding from 192vbr (with EAC and LAME) mp3 down to 80kbs AAC, for a radiohead.

I do listen to a very wide array of music, would there likely be a difference between a symphony and a operatic vocal track? Why would that be?

Oh, and the reason for wanting it all to fit on my nano at the same time is that I travel extensively, and can't always sync up my music. Oh, and I'm kinda OCD.
posted by bluejayk at 4:29 AM on September 23, 2006

Were you using your notebook's speakers? Try playing the songs through the headphones you'd be using with your Nano.

I'm hardly an audiophile but transcoded or low-quality mp3s make me feel physically ill, like the warbly cymbals and mushy sound are throwing off my inner-ear balance.
posted by bcwinters at 6:17 AM on September 23, 2006

MP3 recompression artifacts are to sound what JPEG recompression artifacts are to pictures.

Think blocky. Blocky data, even with the best bitsmoothing algorithms out there tends to make high frequencies warble and make staccato notes muddy.
posted by tomierna at 6:38 AM on September 23, 2006

To hear (extreme) examples of degradation caused by transcoding, see http://heavymeta.org/~wiseman/mp3degen/.

peaches-00.mp3 is the original encoding, MP3 with a variable bit rate. The other files peaches-N.mp3 have been transcoded N times, all at 128 kbps.
posted by jjwiseman at 9:22 AM on September 23, 2006

With 11 gbs of mp3s you can afford to thin some out to be rotated back in later. You have tens of thousands of songs, right?

For what it's worth, my music library takes up 30GB and I have less than 8k songs. I'd guess that he's got more like 2500 songs, which is still something like 7 days straight of music, with no repeats.
posted by chrisamiller at 10:36 AM on September 23, 2006

transcoding is bad because of the way codecs like mp3 work - they try to find the bits that you're probably not going to hear anyway and chop them off (this is really simplified). so, you've done that once when you imported it the first time, and it was pretty OK then, because you had all of the musical data to work with - including a whole bunch of stuff that was there that you can't hear. then, when you take an mp3 and make it, say, a lower bitrate mp3, it's going to try to strip things out and filter and such on already-filtered content, so you'll lose things you probably would hear. (the link jjwiseman posted illustrates.) so, best to re-encode at 80kbit from the original source if you can. (and I'd second listening to them on your headphones if you haven't - I have some stuff encoded at 112kbit and things like cymbols make me want to gnaw my ears off.)

fwiw, I've got a 60 with everything on it - easier than moving lots of music between computers or keeping them all in sync. if you're looking at the 8gb nano, the 30gb iPod is the same price and might be better if you're not going to use it for running or something.
posted by mrg at 10:39 AM on September 23, 2006

I would be very surprised if you couldn't hear how terrible an 80kbps mp3 is. In my experience untrained people can typically hear poor articulation around 96kbps (things go *schnapf* and not so much *snap*).
posted by Matt Oneiros at 11:16 AM on September 23, 2006

Why don't you just set up some smart playlists to fill the player?

On a 8gb player I'd have a 6gb playlist for my highest rated songs, 250mb of the most recently added and 1.75gb of rotated lower rated stuff. (Select if by "least recently played)
posted by chrispy108 at 11:44 AM on September 23, 2006 [1 favorite]

Why not just try it on a couple songs so you can decide whether or not it's acceptable?
posted by 6550 at 12:03 PM on September 23, 2006

I find the new multiple-libraries feature of iTunes very handy. I have a library of over 40gb that has everything I've ever ripped, bought, or downloaded, and a "main" library about half that size that has the music I actually want to listen to. I just import stuff I want from the "big" library, such as holiday or classical music, when I want it in the smaller library. I have a 60GB 5G iPod and like to keep plenty of room for videos and data files.
posted by lhauser at 7:21 PM on September 23, 2006

Re-encode some songs at various bitrates. Heck, reencode the same three or four songs at several different bit rates. Jam them onto your player randomly, play them all, then see if you can really notice a difference when you're listening in a noisy environment.

Seriously, people go nuts over sound quality but we all survived listening to tape walkmans and crappy radio without our ears bleeding. After a while your mind filters it out.

Where it will make a difference - in a quiet room with good headphones when you're paying attention to the music.

Where it won't make a difference - while you're listening to music on standard headphone while concentrating on work in a noisy environment.
posted by tomble at 12:23 AM on September 24, 2006