MirrorMirror
/
headphones
mirror of https://github.com/ploopyco/headphones.git
2
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Shift up the samples into -1..1, not much different, but we get an extra bit of resolution at the low end.

This commit is contained in:
George Norton 2023-09-02 09:22:41 +01:00
parent 354d8e09bb
commit 3beab578b7
1 changed files with 5 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
firmware/code/fix16.inl
View File

@ -32,11 +32,11 @@ static inline fix3_28_t norm_fix3_28_from_s16sample(int16_t a) {
/* So, we're using a Q3.28 fixed point system here, and we want the incoming
audio signal to be represented as a number between -1 and 1. To do this,
we need the 16-bit value to map to the 28-bit right-of-decimal field in
our fixed point number. 28-16 = 12, so we shift the incoming value by
that much to covert it to the desired Q3.28 format and do the normalization
all in one go.
our fixed point number. 28-16 = 12 + the sign bit = 13, so we shift the
incoming value by that much to covert it to the desired Q3.28 format and
do the normalization all in one go.
*/
return (fix3_28_t)a << 12;
return (fix3_28_t)a << 13;
}
/// @brief Convert fixed point samples into signed integer. Used to convert
@ -69,7 +69,7 @@ static inline int32_t norm_fix3_28_to_s16sample(fix3_28_t a) {
/* When we converted the USB audio sample to a fixed point number, we applied
a normalization, or a gain of 1/65536. To convert it back, we can undo that
by shifting it but we output 24bts, so the shift is reduced. */
return (a >> 5);
return (a >> 6);
}
static inline fix3_28_t fix3_28_from_flt(float a) {