REPORT ON THE RELATIVE QUALITY OF AAC AUDIO TO MP3 PART 2. After a very warm response to Part 1 of this test, I decided it was important to do a follow-up test to address many of the suggestions and criticisms. My intention with the original exercise was to compare Apple's implementation of the AAC format to the MP3 standard. Since it is also the format used on the iTunes Music Store which has proved very popular and is now the standard for online music distribution, it was also important to gauge approximately how good the quality of those purchased files was going to be. The purpose of this test is to compare more codecs at a low, medium and high bit rate. I think from this sampling it will be easy to estimate where other bit rates fit in with various types of music. I chose what is probably the most common hi-fi test track - So What from Miles Davis' Kind of Blue. Besides being very well recorded, it is also easily accessible and I encourage you to repeat the test for yourself to form your own opinions. The tracks were reconverted to AIF using Quicktime, burned to CD using Toast, and tested on my home stereo as in the first test. Here are my results: (title shows bit rate, format - application - setting) (ratings are first non-blind, then blind, both out of 10 except total, out of 40) 128 kbps MP3 - iTunes - standard Bloated bass, no treble, very flat, no dynamics, very grainy cymbals, wishy washy imaging. Tonal Accuracy - 4, 5 Imaging/Soundstage - 3, 2 Naturality - 3, 2 Musicality - 6, 4 Total - 16 (normal) | 14 (blind test) 128 kbps AAC - iTunes - standard Unlocalized bloated bass, very rolled treble, cymbals very muted, timid, very flat. Absolutely horrible. Tonal Accuracy - 4, 5 Imaging/Soundstage - 2, 4 Naturality - 1, 2 Musicality - 1, 3 Total - 8 | 14 128 kbps AAC - QuickTime - best Much better treble, pleasing imaging but still rolled treble. Not bad overall. Tonal Accuracy - 6, 7 Imaging/Soundstage - 5, 7 Naturality - 4, 7 Musicality - 6, 8 Total - 21 | 29 128 kbps MP3 - NMP3 - constant bit rate, lame Bloated bass, too much low-mids, lack of bass definition. Rolled treble. Midrange acceptable. Tonal Accuracy - 4, 6 Imaging/Soundstage - 6, 5 Naturality - 4, 2 Musicality - 4, 2 Total - 18 | 15 128 kbps OGG - OggDrop - variable bit rate Better high treble, good bass quality and definition. Some sparkle even. Let down by some very odd phase effects however. Tonal Accuracy - 7, 8 Imaging/Soundstage - 4, 6 Naturality - 6, 8 Musicality - 6, 8 Total - 23 | 30 192 kbps MP3 - iTunes - standard Light bass, rather flat and mechanical. Better treble and imaging than previous but still very closed in. Tonal Accuracy - 6, 7 Imaging/Soundstage - 5, 6 Naturality - 5, 6 Musicality - 5, 5 Total - 21 | 24 192 kbps AAC - iTunes - standard More natural, but still something opaque about the whole thing. Tonal Accuracy - 7, 7 Imaging/Soundstage - 6, 8 Naturality - 7, 7 Musicality - 6, 6 Total - 26 | 28 192 kbps AAC - QuickTime - best Bass a little light, pretty good imaging. Tonal Accuracy - 7, 7 Imaging/Soundstage - 7, 6 Naturality - 8, 7 Musicality - 7, 5 Total - 29 | 25 196 kbps MP3 - NMP3 - vbr, best First nice piano timbre. Bass very even and detailed. Good overall detail. Still a little closed but nice extended treble. Tonal Accuracy - 8, 8 Imaging/Soundstage - 8, 8 Naturality - 8, 8 Musicality - 8, 8 Total - 32 | 32 192 kbps OGG - OggDrop - vbr Bass too light, not defined. No sparkle but still musical. Some weird treble artifacts like white noise. Tonal Accuracy - 7, 7 Imaging/Soundstage - 7, 8 Naturality - 6, 7 Musicality - 8, 7 Total - 28 | 29 320 kbps MP3 - iTunes - standard Bass rather one-notey. Good imaging but flat dynamics. A little uninvolving. Better treble detail than previous. Tonal Accuracy - 8, 7 Imaging/Soundstage - 7, 7 Naturality - 6, 6 Musicality - 7, 4 Total - 28 | 24 320 kbps AAC - iTunes - standard Light bass, poor definition. Pretty good treble. Dynamics good. Fairly involving. Tonal Accuracy - 7, 7 Imaging/Soundstage - 7, 7 Naturality - 7, 6 Musicality - 7, 2 Total - 28 | 22 AIFF (in comparison) It's quite plain to hear the difference between any of these formats and the original. In the blind test I didn't even listen through the whole song before I was convinced I knew the original and it turned out to be the second track I heard. An obvious cue comes from an unlikely place - the tape hiss. In the original it is rather ungloriously extended into the upper reaches of the treble. On all the compressed formats it sounds simply chopped off. The same goes for all the instruments. The top end that gives instruments life, specifically the piano is just gone so you lose much of the tactility that should be giving you that live feeling. Read Part 3