Message-ID: <44561FB6.5000306@xmission.com>
From: Brad Midgley <bmidgley@xmission.com>
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To: bluez-devel@lists.sourceforge.net
Subject: Re: [Bluez-devel] Motorola HT820 audio fidelity
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Date: Mon, 01 May 2006 08:48:22 -0600

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.

> So, at least it's not a hardware or BT stack problem. Is this an
> inherent problem in SBC, or is there a way to tune the encoder to
> compensate? Is it possibly so that a better encoder could be written
> altogether?

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.

Brad


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