Message-ID: <445991B0.9030208@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: Wed, 03 May 2006 23:31:28 -0600

Fredrik

>>> 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?
>> You can get it but you probably need to be logged into a (free) account:
>>
>> https://www.bluetooth.org/foundry/adopters/document/A2DP_Bitstream/en/1/A2DP_Bitstream.zip
> 
> I could get it without an account. I find it rather weird that google
> didn't find it, but oh well.

google won't necessarily "deep link" into sites like bluetooth.org

> Anyway, I tried it, and it was an *enormous* difference. It is true that
> the file encoded by the encoder from bluetooth.org is almost twice as
> large as that encoded by sbcenc as well, but nonetheless, the difference
> in audio quality was huge.

twice as large? could be they're using 4 subbands.

maybe our defaults are too lossy. after calling sbc_init, you can change
sbc.subbands (default 8), sbc.blocks (default 16), sbc.bitpool (default
32). subbands can be 4,8. blocks can be 4,8,12,16. i need to check the
spec on bitpool ranges.

>> we can also compare with our floating point implementation which we have
>> more faith in.
> 
> Is this in the CVS tree? I can't seem to find any other encoder than
> sbcenc. (Speaking of which, what's the difference between the "sbc" and
> "sbc32" directories?)

a lot of this will change, but for now, "sbc" has floating, 64-bit
fixed, and 32-bit fixed and chooses one at compile time. you'll get
floating point implementation if you configure without --enable-fixed.
(heh, maybe that's what you're getting even now)

sbc32 was the precursor to separating out the library and has only the
32-bit implementation. it probably isn't even being built.

a2play "sort of" has a flag for choosing encoder settings (-t for
thrifty) but it is pretty rough.

brad


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