now, I know this sounds like its about speakers, but that just happens to be where I started with this. I wonder if there are any tec savvy folks out there who can perhaps answer this.
I play MP3 (256Kb/s sometimes as VBR with floor limit of 160Kbs) on my Nokia E72 and was listening to speakers (Pioneer BTS5 ones) and noticed that the highs were a little 'wrong' (Vangelis track, Alpha off Albedo 0.39) ... so I whacked on my headphones (socket on the phone) and noted it was much clearer.
A little digging revealed that Bluetooth A2DP actually seems to support sending data in a few formats, like MP3 and AAC format.
Hmm, so I started thinking (too late I guess) and thought that given the spec is AAC that the phone could be doing some sort of cross encoding from what my native MP3 is.
I notice however that when playing stuff at 128Kb/s that the phone has a greater 'range' from the speakers than playing 256. This implies to me that greater bandwidth is needed and so the Bluetooth connection requires a better 'signal to noise' on the analog Tx/Rx side of the data transfer. Meaning that it may be sending the data at the higher rate.
If it is at the higher rate, then that either means that the Pioneer speakers have an inferior DAC in them to my Nokia or that the analog audio bits on the Pioneer speakers are inferior to my Bose headphones ... equally likely.
Does anyone know?