Re: [RFC/PATCH] sbc: new filtering function for 8 band fixed point encoding

Jim Carter
2008-12-02T20:15:20Z

On Fri, 28 Nov 2008, Jaska Uimonen wrote:

> I did some testing on the current 8 band fixed point
> encoding and it seems to attenuate frequencies below 800Hz
> and above 18kHz. There might be some other stuff happening
> also, because at least to me the bass seemed to lack some
> "definition".

I have the same subjective impression: on (inexpensive) Motorola HT-820
phones, A2DP is noticeably anemic compared to the same phones with the
provided wire.

> I didn't quite understand how the current tables are calculated
> and how the filtering works so I wrote a new filtering function
> and calculated new filter tables for it. It is written
> using 16 bit fixed point without any platform specific optimizations.
> I only unrolled some loops etc. I tried to follow the
> flow chart in MPEG-1 annex c.

This is very exciting! But it's been about 1.5 years since I read the A2DP
spec so I can't remember: does the headphone require standard band
breakpoints? Or are the breakpoints implicit in the encoding, so if you
adjust them to make better use of the Bluetooth bandwidth, the headphone
will automatically go along?

James F. Carter Voice 310 825 2897 FAX 310 206 6673
UCLA-Mathnet; 6115 MSA; 405 Hilgard Ave.; Los Angeles, CA, USA 90095-1555
Email: jimc@math.ucla.edu http://www.math.ucla.edu/~jimc (q.v. for PGP key)