6 Apr
2011
6 Apr
'11
9:05 p.m.
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 could be causing this? The signal path is Ogg Vorbis files to Android phone
(obligatory Linux content!) to A2DP stereo headset.
Also, I'm very much enjoing the best of 2010 mix! The quality of the music is
excellent.
I have it on shuffle along with the latest Radiohead record, and I cannot tell which is
the multi-mega-superstar-major-label-millionaire-rock-band release, and which is a guy in
his bedroom knocking stuff out on his laptop for fun in spare hours after work. Linux
audio is definitely as ready for prime-time as the prime-time is.
I digress, but nonetheless, I will BOX THE EARS of anyone who diverts my precious thread
into discussions of apocalypse, conspiracies, or revolution. You have been warned :-)
-ken
7 Apr
7 Apr
2:49 a.m.
On 7 April 2011 07:04, Ken Restivo <ken(a)restivo.org> 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 could be causing this? The signal path is Ogg Vorbis files to Android phone
(obligatory Linux content!) to A2DP stereo headset.
i'd take a punt that this is a best-effort (as opposed to time
guaranteed) protocol - i.e. "we will get the data there, no guarantees
when" and that something else is taking priority. the a2dp article on
wikipedia talks of using QoS to get better audio delivery, so maybe
that's your answer?
i imagine a2dp was only ever designed to transmit low-bandwidth audio
like phone calls/poor quality mp3 - are you playing a high bitrate
file?
anyway, that's my 'inferred guess' answer
--
robin
http://tangleball.org.nz/ - Auckland's Creative Space
http://openstreetmap.org.nz/ - Open Street Map New Zealand
http://bumblepuppy.org/blog/
4 May
4 May
11:19 a.m.
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).
9:28 p.m.
On Wed, May 04, 2011 at 12:15:57PM +0300, Kai Vehmanen wrote:
Hi,
On Wed, 6 Apr 2011, Ken Restivo wrote:
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
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).
4953
days inactive
4981
days old
linux-audio-user@lists.linuxaudio.org
3 comments
3 participants
participants (3)
-
Kai Vehmanen -
Ken Restivo -
Robin Paulson