From 5171ebb35a96a5da5957e80e702a51a5bfc8ccdb Mon Sep 17 00:00:00 2001
From: Alexander Babikov <lemondrops358@gmail.com>
Date: Fri, 27 Aug 2021 17:23:42 +0500
Subject: [PATCH] Add a filter for CD de-emphasis, with coefficients calculated
based on SoX's code
This only adds the filter itself and needs hooking up to the rest of the code
---
src/include/86box/filters.h | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)
diff --git a/src/include/86box/filters.h b/src/include/86box/filters.h
index ff11a05d4..98eff66e2 100644
--- a/src/include/86box/filters.h
+++ b/src/include/86box/filters.h
@@ -299,6 +299,37 @@ static inline double high_cut_iir(int c, int i, double NewSample) {
return y[c][i][0];
}
+/* fc=5.283kHz, gain=-9.477dB, width=0.4845 */
+static inline double deemph_iir(int i, double NewSample) {
+ double ACoef[NCoef+1] = {
+ 0.46035077886318842566,
+ -0.28440821191249848754,
+ 0.03388877229118691936
+ };
+
+ double BCoef[NCoef+1] = {
+ 1.00000000000000000000,
+ -1.05429146278569141337,
+ 0.26412280202756849290
+ };
+ static double y[2][NCoef+1]; /* output samples */
+ static double x[2][NCoef+1]; /* input samples */
+ int n;
+
+ /* shift the old samples */
+ for(n=NCoef; n>0; n--) {
+ x[i][n] = x[i][n-1];
+ y[i][n] = y[i][n-1];
+ }
+
+ /* Calculate the new output */
+ x[i][0] = NewSample;
+ y[i][0] = ACoef[0] * x[i][0];
+ for(n=1; n<=NCoef; n++)
+ y[i][0] += ACoef[n] * x[i][n] - BCoef[n] * y[i][n];
+
+ return y[i][0];
+}
#undef NCoef
#define NCoef 2