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The ASA ruled that a poster - 'AOL 9.0 on broadband featuring: Radio@AOL. Over 100 CD quality radio stations' - implied 'absolute equivalence between the audio quality of the broadcast and uncompressed CD sound'. This, the authority said, had not been proven and the claim could mislead.

AOL's radio streams are encoded in 64-bit AAC. In its submission to the ASA the company argued with evidence from several independent

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websites that 128-bit MP3 audio is generally considered to be of CD quality. It then produced results from a double blind test which showed that there was no perceptible drop in sound quality between Radio@AOL and 128-bit MP3s. QED, 64-bit AAC radio broadcasts could be described as CD quality.

The ASA, however, did not agree, noting that AOL's test had not directly compared 64-bit AAC with CD sound. It consulted results from controlled listening tests that compared various audio codecs with CD sound.

Its ruling concluded: 'Although it understood from expert advice that some listeners might consider AAC encoding at 64kbps to be broadly equivalent to sound recorded on CD, the Authority also understood that audio quality recorded on CD could vary and some listeners, in particular listening circumstances, might perceive a difference between the broadcast service and the best audio quality that could be delivered using the CD medium.'

AOL was advised to amend the advertisement.