devs/foxbox
1
0
Fork 0
forked from len0rd/rockbox
Code Pull requests Activity

More sane fixed point format for Q parameter.

Browse source 
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@8535 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Thom Johansen 2006-02-02 20:04:02 +00:00
parent 440d75f938
commit 9b4b4d0bf2
1 changed files with 4 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

8
apps/eq.c
View file

@ -132,7 +132,7 @@ static long dbtoA(long db)
/* Calculate second order section peaking filter coefficients.
cutoff is a value from 0 to 0xffffffff, where 0 represents 0 hz and
0xffffffff represents nyquist (samplerate/2).
Q is an unsigned 6.26 fixed point number, lower bound is artificially set
Q is an unsigned 16.16 fixed point number, lower bound is artificially set
at 0.5.
db is s15.16 fixed point and describes gain/attenuation at peak freq.
c is a pointer where the coefs will be stored.
@ -141,7 +141,7 @@ void eq_pk_coefs(unsigned long cutoff, unsigned long Q, long db, long *c)
{
const long one = 1 << 28; /* s3.28 */
const long A = dbtoA(db);
const long alpha = DIV64(fsin(cutoff), 2*Q, 25); /* s1.30 */
const long alpha = DIV64(fsin(cutoff), 2*Q, 15); /* s1.30 */
long a0, a1, a2; /* these are all s3.28 format */
long b0, b1, b2;
@ -164,7 +164,7 @@ void eq_ls_coefs(unsigned long cutoff, unsigned long Q, long db, long *c)
{
const long one = 1 << 24; /* s7.24 */
const long A = dbtoA(db);
const long alpha = DIV64(fsin(cutoff), 2*Q, 25); /* s1.30 */
const long alpha = DIV64(fsin(cutoff), 2*Q, 15); /* s1.30 */
const long ap1 = (A >> 5) + one;
const long am1 = (A >> 5) - one;
const long twosqrtalpha = 2*(FRACMUL(fsqrt(A >> 5, 24), alpha) << 1);
@ -191,7 +191,7 @@ void eq_hs_coefs(unsigned long cutoff, unsigned long Q, long db, long *c)
{
const long one = 1 << 24; /* s7.24 */
const long A = dbtoA(db);
const long alpha = DIV64(fsin(cutoff), 2*Q, 25); /* s1.30 */
const long alpha = DIV64(fsin(cutoff), 2*Q, 15); /* s1.30 */
const long ap1 = (A >> 5) + one;
const long am1 = (A >> 5) - one;
const long twosqrtalpha = 2*(FRACMUL(fsqrt(A >> 5, 24), alpha) << 1);