Subject: Re: [Bluez-devel] Motorola HT820 audio fidelity
From: Fredrik Tolf <fredrik@dolda2000.com>
To: bluez-devel@lists.sourceforge.net
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Date: Tue, 02 May 2006 13:02:06 +0200

On Mon, 2006-05-01 at 08:48 -0600, Brad Midgley wrote:
> Fredrik
> 
> >>It doesn't help that we're typically decoding mp3 and reencoding in sbc.
> >>Loss is really compounded.
> > 
> > 
> > Indeed, that seems to be the problem. I was always under the
> > (uninformed) impression that SBC was lossless, but I just tried
> > re-encoding an MP3 to SBC and playing that SBC with sbcenc and sbcdec,
> > and the exact same audio artifacts are showing themselves when I play
> > back to my normal speaker system as through the headphones.
> 
> You haven't ruled out our implementation of sbc however. We could have
> problems still. Also, there are also some defaults for encoding that
> although set fairly high are not at the max iirc.
> 
> There is/was a reference SBC encoder that is a windows executable
> somewhere at bluetooth.org. Testing with it would let us rule out (or
> implicate) our implementation.

I have Windows in a VMware exactly for things like these, so I could
test that. However, I could find no such thing on bluetooth.org. In
fact, googling for "sbc site:bluetooth.org" only yielded two
insignificant results, so I'm beginning to wonder if I'm doing something
wrong (whatever that'd be...). Any pointers?

> The spec allows us to negotiate a different codec with the headset. SBC
> is the only required codec. fwiw, I've never seen a headset that accepts
> mp3 or others. I should modify a2play to flag these so they would be
> easier to spot.

Unfortunately, that seems to be no relief in this case. a2play gets only
one acp_seid_info from the headset, so I guess that means that it only
supports SBC, correct?

Fredrik Tolf


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