Re: [Bluez-devel] Advanced Audio Distribution Profile (A2DP)

[Brad Midgley <bmidgley@xmission.com>]

Victor,

I am going to have a whack at adding fixed point tables and making the 
decoder optionally use fixed point. I will let you know.

Brad

Victor Shcherbatyuk wrote:
> Hello all,
> 
> Today I was playing with the timeout. None of the values I've tried
> gives good results for HP headphones. Bigger values as I undestand lead
> to a buffer underrun in the headphones (same sound as I get with fp
> emulation on), while smaller values  lead to frame(sample?) drops on the
> headphone side (it kind of sounds faster, but I thing it just drops the
> samples)? The only thing that is stable are breaks in the music I have
> now and then. From another side, with Bluewalker, with the magic "87" it
> sounds almost the same as with HP headphones (so still break now and
> then), but if I reduce timeout by changing e.g. 87 -> 40 it becomes good
> and there is no difference from the PC. That makes me think that there
> is something to do with the buffering model used for these headphones. I
> still want to chek it.
> 
> The next step is the fixed point. As I understood Brad is already
> looking in to it? Cause I also wanted to look into it somewhere in short
> time...
> 
> Regards,
>        Victor.
> 
> -----Original Message-----
> From: bluez-devel-admin@lists.sourceforge.net
> [mailto:bluez-devel-admin@lists.sourceforge.net] On Behalf Of Brad
> Midgley
> Sent: Tuesday, June 21, 2005 20:03 PM
> To: bluez-devel@lists.sourceforge.net
> Subject: Re: [Bluez-devel] Advanced Audio Distribution Profile (A2DP)
> 
> i was hoping to get the timing problem hammered by using setitimer. 
> unfortunately, there still seems to be some dependency on the cpu speed
> which is surprising to me. there's a place in the code where the time
> period reported by libsbc is multiplied by 87/100. that 87 has to be
> tweaked for different cpus :(
> 
> i came by the 87 by using my 1.4ghz pentium-M with the hp headset.
> 
> the iphono and itech headsets are very forgiving with timing. they also
> seem to have the worst problems with audio delay.
> 
> 
>>>1) Is there anyone buse with sbc fixed point convertion?
>>
>>We need an integer only implementation of SBC. I may repeat myself, 
>>but I am not going to code this. This must be done by someone else.
> 
> 
> i started trying to do this with a library (gnu mp). the library is
> really meant for arbitrary-sized numbers, and not so great with short
> floats. if i had a reference implementation of soft floating point in C,
> i could dig into this again. i might try it without but i would have to
> reinvent the normalizing floats after multiply/divides.
> 
> 
>>>2) Is there anyone with similar problems (out-of-synch sound) and 
>>>knows how to solve it (or is it just about tuning the timer?)?
> 
> 
> yes, we found out pretty soon that the hp headset insists on that "87" 
> to be tuned for different cpus. maybe there is something wrong with how
> i did the timer or maybe itimer is not a great route to go.
> 
> i also have an arm board that i am trying to use with this stuff. it can
> *receive* audio if the encoder settings are turned way down but can't
> transmit a2dp. see
> 
>   http://bluetooth-alsa.sourceforge.net/embed.html
> 
> 
>>You need to encode the SBC frames in advance and then use a timer for 
>>sending them. I am working on a ALSA plugin that will do exactly this,
> 
> 
>>but I think that won't help you on your embedded platform.
> 
> 
> i'm very excited to see this part. go, Marcel! and hopefully you can let
> us see what this work looks like soon :)
> 
> Brad
> 
> 
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