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iTunes Match (how good is 256Kbps AAC?

post #1 of 37
Thread Starter 

Neat idea...can anyone comment as to the expected sound quality with their streaming of 256Kbps AAC? (iTunes Plus)

 

As compared to, say, CD quality, or flac?  Thanks!

post #2 of 37

It obviously won't sound as good as cd quality or flac. It'll sound decent though.

post #3 of 37
Quote:
Originally Posted by pmc64 View Post

It obviously won't sound as good as cd quality or flac. It'll sound decent though.

Not "obviously". I don't remember reading about anyone being able to tell the difference between AAC 256 kbps VBR and FLAC in an ABX test. It most likely will sound exactly the same.
Edited by skamp - 3/14/12 at 2:30am
post #4 of 37
Thread Starter 

Interesting.....

 

I listen to Sirius Satelite Radio online regularly which comes in at 128 Kbps.  It sounds pretty good for streaming radio, but without having really done a critical comparison, off the top of my head Id say it sounds like a 128K Mp3 file.

So at 256, it probably sounds decent.  Which makes iTunes Match an attractive proposition if you have a big library of lossy Mp3s in your iTunes library, as they will stream you back the same songs you already have, but in 256K quality.  28 bucks a year.  Hmm.

post #5 of 37
Mind that iTunes Match seems to have a rather annoying limitation right now: "explicit" versions of songs seem to be replaced with "clean" versions, I don't know if Apple has managed to work around it yet.
post #6 of 37

FLAC is lossless compression, so it sounds to most people exactly like the original.  256K is lossy and does not provide an exact replica.  The A CD is by definition the most common source for uncompressed music, and FLAC off CD is very good.  FLAC can also support hi def audio like 24/96.

 

256 sounds good, but there is a clear difference between it and FLAC off of a good source.  I usually rip my CDs in ALAC, which is Apple's lossless, then compress to 256 (new feature in iTunes to downsample to 256 instead of just 128) to jam more tunes onto my iPod for the gym or for travel.

 

EDIT: 256 usually sounds flatter in soundstage and dynamics.  It doesn't offend (except sometimes mass strings), but it doesn't engage as well either...


Edited by mrspeakers - 3/14/12 at 11:21pm
post #7 of 37

This is an old link, but one of my favorites to refer people to when asking about computer based compression formats:

 

http://www.stereophile.com/features/308mp3cd

post #8 of 37
That article is highly misleading. You don't listen to a perceptual codec by looking at graphs. The differences are in the vast majority of cases not audible. Aside from maybe some very specific "killer" samples, AAC ~256 kbps VBR will be transparent, i.e. audibly undistinguishable from the CD.

The whole point of a perceptual codec is to fool your ears, not your eyes.
Edited by skamp - 3/17/12 at 12:01am
post #9 of 37


 

Quote:
Originally Posted by skamp View Post

That article is highly misleading. You don't listen to a perceptual codec by looking at graphs. The differences are in the vast majority of cases not audible. Aside from maybe some very specific "killer" samples, AAC ~256 kbps VBR will be transparent, i.e. audibly undistinguishable from the CD.
The whole point of a perceptual codec is to fool your ears, not your eyes.


 

I don't think the point of the article is to state that numerical objective measurements is representative of a listener's subjective experience; that conversation would be way to involved and not appropriate for this thread/forum section.  I think as educated consumers (which I think most people who post on these forums are) we can read this information and come to our own conclusions without being swayed to much by the results presented to us.

 

The take away that I got from it, is that given identical bit rates, AAC is a 'better' codec then MP3 is in terms of  what the designers of the codec decided was important information to keep and what was OK to discard (better in that it retains more sonicly 'pertinent' information).  As with all compression algorithms there is a give and take in the attempt to balance file size with transparency of the encoding and despite the give and take, I think both mp3 and AAC both offer good-excellent transparency for the file size (esp in a streaming and/or low storage capacity setting which is the situation the OP was talking about).

post #10 of 37
Thread Starter 
Quote:
Originally Posted by GloryUprising View Post


 



 

I don't think the point of the article is to state that numerical objective measurements is representative of a listener's subjective experience; that conversation would be way to involved and not appropriate for this thread/forum section.  I think as educated consumers (which I think most people who post on these forums are) we can read this information and come to our own conclusions without being swayed to much by the results presented to us.

 

The take away that I got from it, is that given identical bit rates, AAC is a 'better' codec then MP3 is in terms of  what the designers of the codec decided was important information to keep and what was OK to discard (better in that it retains more sonicly 'pertinent' information).  As with all compression algorithms there is a give and take in the attempt to balance file size with transparency of the encoding and despite the give and take, I think both mp3 and AAC both offer good-excellent transparency for the file size (esp in a streaming and/or low storage capacity setting which is the situation the OP was talking about).



Well put.   I also agree with skamp. Allow me to keep the idea of my original post in perspective.  If I want top quality for home listening, I'll buy the CD and rip hi-res files to my laptop and use my DAC. My old MP3s are more for background listening, I dont care enough about 1/2 of them to even condider purchasing hi-res versons of them. 


Edited by Skidood - 3/17/12 at 2:24pm
post #11 of 37
Quote:
Originally Posted by Skidood View Post

Interesting.....

 

I listen to Sirius Satelite Radio online regularly which comes in at 128 Kbps.  It sounds pretty good for streaming radio, but without having really done a critical comparison, off the top of my head Id say it sounds like a 128K Mp3 file.

So at 256, it probably sounds decent.  Which makes iTunes Match an attractive proposition if you have a big library of lossy Mp3s in your iTunes library, as they will stream you back the same songs you already have, but in 256K quality.  28 bucks a year.  Hmm.



Isn't satellite radio 64kbps AAC-HE...?

post #12 of 37
Thread Starter 

I can't recall where I saw that it is streamed at 128 Kbps.  Keep in mind this was for online listening, not actually using a satelitte radio.

My guess is that what I actually read was implying that  (even though I recall it being really vague)  the source file quality at Sirius  is 128 Kbps, but it is streamed at whatever rate is needed.

I fired it up and after waiting for several minutes to allow for buffering, I measured the data rate coming into my laptop using the properties screen of my wireless connection and a stopwatch.  It was 16.7 Kbps.  Hmm.

post #13 of 37
Quote:
Originally Posted by Skidood View Post

I can't recall where I saw that it is streamed at 128 Kbps.  Keep in mind this was for online listening, not actually using a satelitte radio.

My guess is that what I actually read was implying that  (even though I recall it being really vague)  the source file quality at Sirius  is 128 Kbps, but it is streamed at whatever rate is needed.

I fired it up and after waiting for several minutes to allow for buffering, I measured the data rate coming into my laptop using the properties screen of my wireless connection and a stopwatch.  It was 16.7 Kbps.  Hmm.



You sure that wasn't measured in KBps?  16KBps is 128Kbps.

 

But I think the actual satellite data streams are 64Kbps, the bandwidth is extremely limited and it has to be shared among the many different channels.

post #14 of 37
Thread Starter 

Aaahh...nice catch.....it was actually 16,667 bytes per second.  Using 1024 to divide makes it 16.28 KBps.

 

What can I take from this info relating to quality of the files being streamed?  I guess it would depend on which compression format they use....

 

The sound is definitely better listening online vs. using the satelite radio.


Edited by Skidood - 3/18/12 at 7:48am
post #15 of 37

if the 256kbps AAC VBR or CBR whatever they do was ripped from a CD or made from the original lossless file(99.9% what has to be done) then..most can't tell the difference. Most head-fier's cant tell the difference between anything 256kbps+ be it AAC or MP3 and lossless. ABX with foobar will give you a definite answer, i got a 1.1% at the end after an hour of siting there and doing an ABX so i guess i can hear the difference but believe me...even if i got that score. i would still not mind listening to 256kbps...it's so hard to tell. the difference wasn't big. heck one from the other didn't sound bad. they both sounded good, it's just that the 256kbps sounded a bit "different" but not bad from the lossless rip.

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