EMI/Apple announcement of forthcoming sales of DRM-free and higher quality AAC 256kbit/s songs from iTunes music store is heavily discussed now. While almost everybody agree that this is a move to the right direction (final point probably means reasonably priced lossless downloads) there is no consensus about the reasons of choosing exactly 256 kbit/s. This bitrate seems too high for an average listener (which is quite happy with existing AAC 128kbit/s) and the same time it’s definitely inadequate for demanding listeners especially taking into account that Apple’s AAC encoder is not state-of-the-art one. Most prolate guesses explaining the choice are:

• Stimulation of higher-cappasity iPod sales as increased bitrate needs doubling of memory size for storing music
• Cleaver decision from the marketing standpoint – consumer gets twice as good sound quality for only 30% price increase. Now songs look even cheaper
• Stimulation of legal downloads as they are of better quality than most music in P2P networks (128-192kbit/s)
• Getting of additional advantage over Microsoft since many digital audio players supporting WMA are limited by 192kbit/s for this audio format
• Providing with some headroom for inserting watermarks which can help to track iTunes songs in P2P networks

Watermarking point seems to be a wild assumption though because …. Apple has much wiser marketing strategy than the RIAA does. It will take (let me guess) one week for A-students from any university campus to discover the fact and the principles of watermarking used and one week more for internet community to discuss possible consequences for file-sharers, music industry and Apple itself and to develop methods for destroying watermarked information. After that the whole following year any person interested will throw mud at Steve Jobs and the Co. So watermarking technique is conceived only for research purposes (like birds tagging) which have to be clearly stated beforehand.

SoundExpert contributes its 2 cents to the discussion by adding AAC@256 from the latest iTunes to the rating system. Though new audio metrics used by SoundExpert is still experimental it’s the only testing methodology today capable of measuring perceptual audio quality margin. It helps not only to grade the quality of AAC@256 audio format but also to compare it with other formats such as mp3 or wma at different bitrates.

Blind listening tests conducted over the internet are essential part of the new metrics. These tests designed in a way that everyone, including you, can participate. Just download a test file, listen it and feedback your grade (all details inside test file). Downloading a test file from SoundExpert you can get randomly one of 93 audio codecs rotated in the system at the moment including newly added AAC 256 kbit/s codec from iTunes.

First results for the rating are available on “Coders 256 kbit/s” page. Light-grey color of the bar indicates low reliability of the rating caused by insufficient number of returned grades. In order to be reliable each rating needs about 300 test files to be downloaded and graded. So, it will take some time (depending of volunteer testers’ activity) to get final results for iTunes AAC@256 codec.