[Bluez-devel] headset audio playback real slooowwww

[Bluez-devel] headset audio playback real slooowwww

[Koster Ken]

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I'm fighting a problem that I hope someone here can help with.

For reasons I won't go into here I'm stuck with an environment based off of
Kernel 2.6.10 running on an arm processor. I have been able to upgrade 
bluez-lib and bluez-util to 3.19 and I'm attempting to make use of the 
audio service to send audio to a bluetooth headset.

Everything is working with the exception that the playback is at half the
normal speed, so everything recorded is lower in pitch and takes twice
as long.  (a seven second sound sample takes fourteen to play back)

We're playing a sound sample I recorded on my laptop with arecord, it's a
u8 sample and plays back perfectly on the laptop.

Using hcidump and comparing the data being sent on the laptop with that on
the arm system shows the identical SCO data stream.  The only difference 
we can really see is that the laptop sends an 'HCI Command: Read Remote
Supported Features" to the headset while the arm system doesn't.  This
appears to be due to changes in the kernel code.  I managed to patch the
kernel code to add this (and only this) but it makes no difference.  A hack
I know, but we're getting desperate :-)

Using aplay -v -Dplug:bluetooth sample.u8  shows the identical pcm structure
and setup as the laptop.   Plug PCM: linear conversion PCM (S16_LE) followed
by Slave: Bluetooth Audio Device.

Any suggestions as to where I should concentrate? 

-- 
Ken Koster
Senior Software Engineer

EB - Discover the Experience 
22745 29th Dr. SE, Suite 200
Bothell, WA 98021, USA 
Tel: +1 425-444-2691 
Fax: +1 425-686-3102 
ken.koster@elektrobit.com 
www.elektrobit.com


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Re: [Bluez-devel] headset audio playback real slooowwww

[Jim Carter]

On Fri, 9 Nov 2007, Koster Ken wrote:

> bluez-lib and bluez-util to 3.19 and I'm attempting to make use of the 
> audio service to send audio to a bluetooth headset.
> 
> Everything is working with the exception that the playback is at half the
> normal speed, so everything recorded is lower in pitch and takes twice
> as long.  (a seven second sound sample takes fourteen to play back)

You mentioned SCO later in the message; this protocol is monophonic.  If 
the sound clip were recorded in stereo (I'm assuming 44100 Hz), with 
independent channels (not joint stereo), then there would be two 
nearly-identical copies of each sound sample, and if you forced it to go 
out as mono, it would play at half speed.  There would be a 22 KHz whistle 
as you alternated between possibly unequal stereo tracks, but since SCO is 
at 8000 Hz, this would be inaudible after the sound stream was resampled 
(or maybe being imaged down to 2 KHz but very quiet due to averaging).  
Maybe that's what happened.

James F. Carter          Voice 310 825 2897    FAX 310 206 6673
UCLA-Mathnet;  6115 MSA; 405 Hilgard Ave.; Los Angeles, CA, USA 90095-1555
Email: jimc@math.ucla.edu  http://www.math.ucla.edu/~jimc (q.v. for PGP key)

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Re: [Bluez-devel] headset audio playback real slooowwww

[Ken Koster]

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On Saturday 10 November 2007, Jim Carter wrote:
> On Fri, 9 Nov 2007, Koster Ken wrote:
> 
> > bluez-lib and bluez-util to 3.19 and I'm attempting to make use of the 
> > audio service to send audio to a bluetooth headset.
> > 
> > Everything is working with the exception that the playback is at half the
> > normal speed, so everything recorded is lower in pitch and takes twice
> > as long.  (a seven second sound sample takes fourteen to play back)
> 
> You mentioned SCO later in the message; this protocol is monophonic.  If 
> the sound clip were recorded in stereo (I'm assuming 44100 Hz), with 
> independent channels (not joint stereo), then there would be two 
> nearly-identical copies of each sound sample, and if you forced it to go 
> out as mono, it would play at half speed.  There would be a 22 KHz whistle 
> as you alternated between possibly unequal stereo tracks, but since SCO is 
> at 8000 Hz, this would be inaudible after the sound stream was resampled 
> (or maybe being imaged down to 2 KHz but very quiet due to averaging).  
> Maybe that's what happened.

Unfortunately the clip is mono, recorded at an 8k rate.

I'm rapidly learning far more about SCO than I ever planned :-)

-- 
Ken Koster
Senior Software Engineer

EB - Discover the Experience 
22745 29th Dr. SE, Suite 200
Bothell, WA 98021, USA 
Tel: +1 425-444-2691 
Fax: +1 425-686-3102 
ken.koster@elektrobit.com 
www.elektrobit.com


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