How much audio quality is lost converting 320kbps MP3 to 128kbps AAC?

kuykee

macrumors newbie
Original poster
May 20, 2010
10
0
How much audio quality is lost converting 320kbps MP3 to 128kbps AAC?

I'd like to know so that I can store more files on my iPhone and iPod classic (also to make the iPod classic hard drive spin less). Also to save space on my Macbook hard disk
 

basesloaded190

macrumors 68030
Oct 16, 2007
2,693
5
Wisconsin
My guess would be that it depends on what kind of headphones you are using. If you are using something along the lines of Apple's earphones, my guess would be not that much. But if you have a $200+ set you might notice the decrease in quality.
 

jamesjingyi

macrumors 6502a
Dec 20, 2011
793
32
UK
Why not test it out yourself

Oh and why not try iTunes Match... Then nothing is on your MB at all and your Classic is fine!
 

sectime

macrumors 6502a
Jul 29, 2007
530
0
Why not test it out yourself

Oh and why not try iTunes Match... Then nothing is on your MB at all and your Classic is fine!
I use 192kpps compression when syncing my IPhone with ITunes. Best trade off in quality vs size for me. Your listening environment is more important than compression for sound quality.
 

scaredpoet

macrumors 604
Apr 6, 2007
6,627
342
there is an option to down convert to 128kbps when syncing to iPods and iOS devices, so you might want to try that. If you don't like it, you can just uncheck the box and resync.
 

alphaod

macrumors Core
Feb 9, 2008
22,177
1,231
NYC
Why would you buy a classic to save space? :confused:


The loss in quality cannot be quantified. You need to physically listen to each song, and it's possible if you have poor headphones, or even a bad hearing, you can't tell the difference.
 

xraydoc

macrumors demi-god
Oct 9, 2005
7,739
1,884
192.168.1.1
On good equipment you will almost certainly hear a difference. How much it bothers you is what matters most.
 

jon3543

macrumors 6502
Sep 13, 2010
483
142
How much audio quality is lost converting 320kbps MP3 to 128kbps AAC?

I'd like to know so that I can store more files on my iPhone and iPod classic (also to make the iPod classic hard drive spin less). Also to save space on my Macbook hard disk
It won't be nearly as bad as converting MP3 to MP3 using LAME, which can produce obvious artifacts after just one generation of transcoding. In fact, high bitrate MP3 to AAC will probably be pretty good. Let your ears be the judge, but please perform valid comparisons using foobar2000's ABX comparator or similar. There are apps that will let you do the comparison right on the Touch.
 

gnasher729

Suspended
Nov 25, 2005
17,123
4,146
How much audio quality is lost converting 320kbps MP3 to 128kbps AAC?

I'd like to know so that I can store more files on my iPhone and iPod classic (also to make the iPod classic hard drive spin less). Also to save space on my Macbook hard disk
Plug in your iPod. In iTunes, click on the iPod. Click on "Summary", and "Convert higher bitrate to 128KBit". That option is non-destructive. Nothing on your hard drive is changed, so you don't have to worry about any loss. iTunes converts the music while it gets downloaded to the iPod. If you don't like it, you just change the option. I cannot distinguish AAC 192KBit from originals. 128KBit loses something. It's not the same.
 

kuykee

macrumors newbie
Original poster
May 20, 2010
10
0
foobar2000 comparator looked interesting, but it's still only listening by ear according to this video http://www.youtube.com/watch?v=jt7GyFW4hOI

Is there something else that can give you a graph or more statistical view of what is being lost from or changed in the file or in which parts there have been changes?
 

lazard

macrumors 68000
Jul 23, 2012
1,608
818
depends on what earbuds/headphones you're using and how good your hearing is. Personally, I would never rip in 128 because it sounds so awful.
 

JAT

macrumors 603
Dec 31, 2001
6,473
124
Mpls, MN
foobar2000 comparator looked interesting, but it's still only listening by ear according to this video http://www.youtube.com/watch?v=jt7GyFW4hOI

Is there something else that can give you a graph or more statistical view of what is being lost from or changed in the file or in which parts there have been changes?
This question and discussion has been ongoing since the 70s. (only the formats have changed) Good luck on receiving an answer.
 

jon3543

macrumors 6502
Sep 13, 2010
483
142
foobar2000 comparator looked interesting, but it's still only listening by ear according to this video http://www.youtube.com/watch?v=jt7GyFW4hOI

Is there something else that can give you a graph or more statistical view of what is being lost from or changed in the file or in which parts there have been changes?
Viewing things like waveform difference files is not particularly relevant. The only thing that matters is your own subjective perception and performing a valid blind test. Besides using foobar ABX or equivalent, the two files to be compared must be derived from the same mastering, and preferably the exact same source (one from the other obviously counts); otherwise, you may be testing for differences in mastering, not encoding, and differences in mastering can be genuinely profound and trivial for anyone to ABX.

There is an infinite amount of nonsense in discussions about these things. Here is a fairly detailed slideshow of a scholarly presentation that used high-end equipment under ideal conditions:

http://www.music.mcgill.ca/~hockman/documents/Pras_presentation2009.pdf

Its conclusion were:

  • Trained listeners can hear differences between CD quality and mp3 compression (96-192 kb/s) and prefer CD quality.
  • Trained listeners can not discriminate between CD quality and mp3 compression (256-320 kb/s) while expert listeners could.
  • Ability to discriminate depends on listeners’ expertise and musical genre.
  • Artifacts can be verbalized and do not depend on musical genre.

I think AAC is a lot better than MP3 at low bitrates, judging by my threshold for hearing artifacts in various "killer samples", which disappear for me at AAC 128 Kbps but persist in LAME 3.98 MP3 up to 192 Kbps and a little beyond. I've also found transcoding high bitrate MP3s to AAC to be much more transparent than going MP3->MP3, which introduces obvious artifacts after one generation. If you want to read a lot of subjective crazy talk including things like cable directionality, try the stevehoffman.tv forums. For people who value blind listening tests, try hydrogenaudio.org.
 

kevink2

macrumors 65816
Nov 2, 2008
1,429
138
For me, where I listen to my iPhone, I don't see that it matters. In my truck, there is enough wind noise that I don't notice.
 

netnewswireuser

macrumors member
Jan 2, 2017
34
31
How much audio quality is lost converting 320kbps MP3 to 128kbps AAC?

I'd like to know so that I can store more files on my iPhone and iPod classic (also to make the iPod classic hard drive spin less). Also to save space on my Macbook hard disk
Well, the real sequence of this conversion is the following:

WAV 44.1khz/16bits -> MP3 320kbps -> WAV 44.1khz/16bits -> AAC 128kbps

In the first transition (from wav to mp3) you are losing audio information, that information is missing when you convert it back to WAV and it cannot be recovered.

Then you lose even more audio information when you convert that "incomplete" WAV to AAC 128kbps.

So you will get pretty crappy audio files, worse than regular AAC 128kbps (they usually came directly form CDs). So you can think of them as 96kbps AAC or maybe worse because different lossy codecs cut different things.

Going from one lossy format to another lossy format is not a good idea.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.