BitRate chooser for iPod

[Gaffer74]

I thought I'd try a quick experiment to test which bitrate I should encode songs onto my iPod.

I created the following versions of the song "Like A Star" by Corinne Bailey Rae (4min 3sec):
1: AIFF , 1411kbps ... 41Mb
2: WAV , 1411kbps ... 41Mb
3: Apple Lossless , 778kbps ... 22.7Mb
4: MP3 , 320kbps ... 9.4Mb
5: AAC , 320kbps ... 9.3Mb
6: AAC , 192kbps ...5.6Mb
7: AAC , 128kbps ... 3.8Mb
8: MP3 , 128kbps ... 3.8Mb

I've also included the file sizes.

I attached to line-in on my second hi-fi and sat in the other room (out of sight...where the speakers are) and got my nephew to play the songs in any order (the hi-fi is situated in the adjoining room).

Despite what I expected, it was usually quite easy to distinguish between them.

I did have trouble distinguishing between AIFF and WAV files.
The Lossless file sounded slightly "sharper", and therefore more "in your face".
Beyond these, there was a clearer reduction in quality in that guitar strings didn't sound quite right, vocals started sounding a bit harsher with the next formats:
AAC 320 sounded very good, but I again found it more difficult to distinguish between MP3 320 and AAC 192. Overall I felt the AAC 192 provided more "air" to the proceedings and was better suited to vocals, but MP3 320 provided more "depth" and gave a better picture of bass....but it was close between them.
AAC 128 was clearly rubbish with distorted vocals and a nasty "equalised boom box" feel to the music.
MP3 128....eeeuuuuurgh, the less said the better. I wouldn't call it music...I would call it noise.

To confirm, I then burnt the tracks onto a CD using Toast Titanium. This re-converted all to aiff format, but the pre-existing formats were the rate limiting step, so any deficiencies would still be heard (and be a function of the format they were converted from...ie a AAC 128 song converted to AIFF will only sound as good as the AAC 128 song did in the first place).
Same results.

So in order of preference, I had (best->worst)
1 = 2
3
5
4 = 6
7
8

...and am glad I stuck with AAC 192 when i first got my iPod a year ago. It offers the same excellent sound of MP3 320 quality, but for much less space (about 40% less).
(The reason I chose to play through the dedicated Hi-Fi is that it should be easier to pick up subtle differences in sound).

I'm also convinced that AAC sounds "good" on the iPod because it is effectively altering the sound similar to what you might get sticking an uncompressed track through an equaliser setting like "acoustic" or "treble booster". That's why it sounded more "airy" imo....but for the purposes of portable audio, it still sounds excellent.

I'm not saying this is any way definitive...just that it works for me and to show how easy it is to do. Remember, at all times, even though I couldn't always distinguish between AIFF and WAV, they were both clearly superior to the others on a dedicated Hi-Fi set-up (which is why I always buy CD's I like rather than download from iTunes/bittorrent).

It's a simple and easy way for you to try yourself to see "how low you can go" before SQ becomes unnacceptable on portable machines.

(i always stick with best SQ possible for my Hi-Fi seperates though )

 

[michaelab]

I did have trouble distinguishing between AIFF and WAV files.

That's hardly surprising as they are the essentially the same format but with a different name. They are both full 16bit/44.1kHz linear PCM, uncompressed.

I'm surprised that lossless sounded different. When it's uncompressed you get back exactly the content of the original AIFF/WAV file.

I personally use MP3 320 for everything except classical where I use Apple Lossless because the MP3 decoder on the iPod (mine is 3rd gen) has a strange bug that can make large MP3 320 files completely unlistenable.

Michael.

 

[robert_cyrus]

for me it was a choice of
6: AAC , 192kbps ...5.6Mb
7: AAC , 128kbps ... 3.8Mb
and i went for 7. purely for space (roughly 2/3rd of the 192 file sizes, as u'd expect at 2/3'rd of the bitrate).

i'm perfectly happy with aac 128's for music "on the move" (or at my desk at work!) and they sound fine with my shuffle and ipod mini.

 

[meme]

Hiya,

This may have been asked before, so please forgive me, but how does Apple Lossless actually retain information when you must be throwing it away?

Cheers, Elton.

 

[PeteH]

how does Apple Lossless actually retain information when you must be throwing it away?

In much the same way as other losslessly compressed formats work, for example .zip or .png. Your basic .wav or .bmp file is robust and simple but mindless - by way of illustration, you'll get a string of 10 1s in a row stored as 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, whereas your lossless format will store it as "10 x 1", or whatever. Basically, no information is discarded, it's just stored more compactly - the degree to which this can be done depends on the nature of the original data, which is why different tracks of the same length compress to different file sizes.

 

[oedipus]

Before commenting on MP3 compression...

MP3 128....eeeuuuuurgh, the less said the better. I wouldn't call it music...I would call it noise.

Before passing judgement on "128kb MP3" it is crucial you understand that the ISO MPEG standards specify what a compliant bitstream is, and DO NOT specify the encoder (ie how to go from audio to [one of many possible] bitstreams).

To shortcircuit a great deal of technical discussion, different MPEG encoders are free to take your audio and create a compliant bitstream in whatever fashion they see appropriate, using whatever psychological model (for audible/inaudible) lossy compression that the authors deem fit.

This means that a 128Kb/s stream out of one encoder (unless sourced from the same encoding vender) is likely to generate a completely different bitstream to another encoder. Both encodings (and encoders) are compliant, and can be played back on a compatible decoder.

HOWEVER, and this is really the point, some encoders at 128Kb/s can generate far better (in the psychoacoustic sense) encodings than other encoders (ie. sound better).

When it comes to audio MPEG encoding, the provenance of your encoder is all.

 

[johnhunt]

I find the sound of my ipod is most influenced by the 171 bus

 

[huuge]

try LAME

I use lame (alt preset standard) mp3 encoder which averages out around the 192 mark but easily betters aac 192
why not give it ago
lame also has higher bit rate presets but the standard seems the best trade off size/quality wise

 

[DennyL]

I would like to see a comparison like this between MP3 and Ogg-Vorbis.

 

[Gaffer74]

I'm surprised that lossless sounded different. When it's uncompressed you get back exactly the content of the original AIFF/WAV file.

Yep, I can't answer that; It was easy to pick it out from the later tracks, but also I found myself able to pick out from the previous two.
As I mentioned, AAC made things sound more "sharp/airy"...good for vocals, but sounded a bit like someone had stuck a normal wav/aiff file through an "acoustic" equaliser. Maybe my last iTunes 'update' did something to the codec?

Oh...and all equalistaion settings were "off" for all tracks (as was that crappy "sound check" option (i used iTunes).

Like I said, the above were my results for me, and it's easy to do so I wouldn't be surprised if everyone else had their own favourites/came to their own conclusions (this is by no means a definitive test....but it does let me decide what encoding I'm happy with myself).

Even though I think AAC leaves it's own 'mark' on the music, I think it's good enough for portable use (i play mine through the car....never normally through the seperates set up at home )

I find the sound of my ipod is most influenced by the 171 bus

:lol: too true (mainly it's the noisy chavs who sit at the back).

 

[jtc]

I went with a mixture of 320kbps AAC and 256kbps AAC on my iPod - 320 for the stuff that I know might benefit from that extra bandwidth. To be fair, it's hard to fault 256 or 320 AAC in anything bar a direct A:B comparison with uncompressed, so I'm happy enough. Maybe if I get a pair of Etymotics I might then be better placed to hear the flaws (I'm using Sony MDR-71s) but until then 256/320 it is. Sod the extra space it takes up, I don't listen to more than about 1/4 of my music collection in any given year anyway, so why lose sleep over it?