linuxaudio.org

On Wed, May 04, 2011 at 12:15:57PM +0300, Kai Vehmanen wrote:

quoted text
> Hi,

>

> On Wed, 6 Apr 2011, Ken Restivo wrote:

>

>> I have been lately using a Bluetooth A2DP headset to listen to music.

>>

>> Every now and then, it drops pitch! It slows the music down, by as much

>> as a semitone, for several seconds, then comes back slowly. I rather

>> like the effect; it's like an old cheap analog vynil turntable with a

>> bad motor or worn belt.

>

> what headset are you using? I recommend getting a different headset if

> you want to get rid of this (or cherish the headset you have, if you like

> the effect ;)).

>

> Some parts of BT A2DP are a bit underspecified and there are some

> interesting implementations of it out there. There is no flow control or

> clock sync used, so the receiver (your headset) should be a proper

> RTP-receiver type of implementation that can adjust to the sender's clock

> and packet transmission rate and adjust for drift, etc.

>

> But there are some headsets that are lazy and make false assumptions on

> the timing characterics of A2DP and the sender. E.g. I've stumbled on

> commercially sold headsets that just play at whatever rate the sender is

> sending. So you get incorrect and _varying_ pitch for all played audio.

> The exact outcome is unique to each sender+receiver combo.

>

> In your case, the headset seems to have some funky underrun/overflow

> logic that tries to periodically catch up, or slow down, in case of clock

> drift (which to some degree always happens).

Yep. It cost all of US$12, shipped directly from Hong Kong (took 3 weeks to get here). Not surprised that it has bugs.
I'm fine with it for now. Thanks for explaining!
-ken

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