Re: [Bluez-devel] sbc and fixed-point progress

Brad Midgley
2005-09-07T03:24:29Z

Victor

> I've checked in code for 4-subbands encoder. I've tried it only on x86,
> but I do not expect any surprises on arm.

Again, this is very cool...

> It turned out (probably I should read the specs more carefully) that
> 4-subbands with the same bitpool are actually superior to 8-subbands in
> sound quality, producing 2 times higher bitrate

wow, I hadn't understood that. I always thought 4 subbands sounded
better just because my stereo headset is the sort of tinny in-the-ear
type and I figured 4 subbands was truncating high-end frequencies just
enough to make the sound less shrill.

> I've added the options to specify the number of subbands and use of
> joint stereo to sbcenc.

ok, good.

> Things to do (I'll spend some time on it):
> 1. Check if joint stereo works
> 2. Add command line arguments for bitpool, subbands, joint stereo,
> other? (thrifty flag is a bit obscure)

yes, "thrifty" was a quick hack

> 4. Check/tune the error introduced by fixed point conversion (this can
> be done comparing to old floating point implementation, cause current is
> using int32_t for subbands, which might introduce some error in the
> output stream)

how is 32 bit maths selected? I assume we have to tweak the source to
try it...

> 5. There are still some optimizations regarding memcopies....

yes... I've been struggling with this in the decoder...