REPORT ON THE RELATIVE QUALITY OF AAC AUDIO TO MP3 PART 3. In Part 1 and Part 2 of this test I looked at the relative quality of AAC to MP3 using various settings and bitrates for each of the compressed formats. To make a long story short none of the "standard" compression means sounded very good and only through more time consuming and advanced methods could you get the formats to sound acceptable. Since I did those two tests a lot has changed in the online music world. The iPod is now the default portable music player and the iTunes Music Store is the default place to get music online. The store uses 128 kbit AAC to encode its tracks so many people now are making significant investments in AAC as a future standard. In my previous tests, I found AAC to be lacking in many ways so I thought it was important to see how it sounded now that people were paying for it. I also was curious if I could hear a difference between Apple's professionally encoded tracks and the same track encoded in iTunes on my Powerbook G4 400. They make claims to be using higher resolution masters in certain cases and many have suggested that they have a more robust encoding algorithm. To encode the songs I first ripped an AIFF in iTunes (4.7 (41) Mac, Quicktime 6.5.2) then converted to either 128 or 192 AAC. The three songs I chose were: 1. Brian Wilson - Heroes and Villains - Smile 2004 2. Leon Redbone - I Hate a Man Like You - Champagne Charlie 3. Miles Davis - So What - Kind of Blue You can go buy these tracks and listen for yourself. Here are my results: BRIAN WILSON - HEROES AND VILLAINS - SMILE 2004 This track has a dense layering and a lot of percussive sounds. iTunes Music Store - 128 kbps AAC Lack of mid-bass weight and "blossoming" warmth. This track has a lot of symphonics and they were rendered fairly cold compared to the CD. Transients and cymbals were harsher and more metallic. Tonal Accuracy - 4 Imaging/Soundstage - 4.5 Naturality - 4.5 Musicality - 4.5 Total - 17.5/20 iTunes Encoder - 128 kbps AAC For some reason this track sounded worse than the same bit rate from the iTunes Music Store. It simply sounded flat. Tonal Accuracy - 4 Imaging/Soundstage - 4 Naturality - 4 Musicality - 4 Total - 16/20 iTunes Encoder - 192 kbps AAC Much better than the 128 tracks and very close to the CD. Only a slight flatness seemed to divide the two. Tonal Accuracy - 4.5 Imaging/Soundstage - 4.5 Naturality - 4.5 Musicality - 4.5 Total - 18/20 LEON REDBONE - I HATE A MAN LIKE YOU - CHAMPAGNE CHARLIE This track has very few instruments and is close-miked. The guitar is one of the best I have heard and the strings can come alive with that tangy metallic sound that you feel in real life. On a good stereo the room can be energized in a similar fashion to the real thing. iTunes Music Store - 128 kbps AAC This bit rate stumbled quite noticeably on this track. The sound was flattened so that the depth and nuance of the guitar was lessened. Tonal Accuracy - 4.5 Imaging/Soundstage - 3.5 Naturality - 4 Musicality - 4 Total - 15.5/20 iTunes Encoder - 128 kbps AAC This track sounded nearly identical to the one I bought from the Apple Music store. There might have been a little less treble definition. Tonal Accuracy - 4 Imaging/Soundstage - 3.5 Naturality - 4 Musicality - 4 Total - 15/20 iTunes Encoder - 192 kbps AAC As with the last song, really quite good. Just a hint of flattening. Tonal Accuracy - 4.5 Imaging/Soundstage - 4.5 Naturality - 4.5 Musicality - 4.5 Total - 18/20 MILES DAVIS - SO WHAT - KIND OF BLUE I decided to carry this track over from the last test because it is so well known and so tough for compressed formats to recreate. The soundstage is huge and the detail in the instruments is almost infinitely layered so it becomes a real chore to dig it all out. As always, the tape hiss presents an interesting standard of its own. iTunes Music Store - 128 kbps AAC This encoding really showed the treble failings of a low bit rate. As I found before, it was like the whole top end was chopped off. Tonal Accuracy - 3.5 Imaging/Soundstage - 4 Naturality - 4 Musicality - 4 Total - 15.5/20 iTunes Encoder - 128 kbps AAC If the official Apple track was bad, this one seemed to go a step further in losing treble detail and soundstaging. Tonal Accuracy - 3.5 Imaging/Soundstage - 3.5 Naturality - 3.5 Musicality - 3.5 Total - 14/20 iTunes Encoder - 192 kbps AAC A much better result than the lower bit rates but still quite noticeably inferior to the original. Tonal Accuracy - 4 Imaging/Soundstage - 4.5 Naturality - 4 Musicality - 4.5 Total - 17/20 CONCLUSION Overall it seems likely to me that Apple has improved its AAC implementation since I first tested it. If someone from the company wants to outline any general changes I would be curious to know but with these songs, to my ears, it sounds better. It's also interesting that the files from the Apple iTunes Music Store seem to have a very slight edge over the ones I encoded on my home computer. As I pointed out before, I think a test like this will be affected to a large degree by the songs that are chosen. I tried to pick a range of things that might give the encoders difficulty. On the whole I would conclude that well recorded tracks with exceptional detail come out the worst when encoded. This follows from common sense but it should give you an idea of how good the music you like might sound. Is it good enough to pay for? You must answer that question yourself. For me, losing 10-25% of the musical information is like losing that much enjoyment and if buying CDs or LPs is as affordable I'm willing to buy those formats to not lose out on anything. For those of you who want to walk the middle ground, I was pleasantly surprised to see that 192 kbps AAC is sounding very good. If you have an iPod I would have no reservations about encoding all my music at that rate. Hopefully as time goes on Apple will do the same. Back to Articles