From cc5b08053f2bab7d6fdcfd06c3bcf5beca1a3f22 Mon Sep 17 00:00:00 2001
From: kub <derkub@gmail.com>
Date: Tue, 4 Feb 2025 22:01:18 +0100
Subject: [PATCH] sound, minor FM filter improvements
---
pico/sound/sound.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/pico/sound/sound.c b/pico/sound/sound.c
index f24572ca..d7de6e9d 100644
--- a/pico/sound/sound.c
+++ b/pico/sound/sound.c
@@ -91,7 +91,7 @@ PICO_INTERNAL void PsndReset(void)
}
// FM polyphase FIR resampling
-#define FMFIR_TAPS 9
+#define FMFIR_TAPS 8
// resample FM from its native 53267Hz/52781Hz with polyphase FIR filter
static int ymchans;
@@ -128,7 +128,7 @@ static void YMFM_setup_FIR(int inrate, int outrate, int stereo)
{
int mindiff = 999;
int diff, mul, div;
- int minmult = 22, maxmult = 55; // min,max interpolation factor
+ int minmult = 11, maxmult = 61; // min,max interpolation factor
// compute filter ratio with largest multiplier for smallest error
for (mul = minmult; mul <= maxmult; mul++) {
@@ -138,7 +138,7 @@ static void YMFM_setup_FIR(int inrate, int outrate, int stereo)
mindiff = diff;
Pico.snd.fm_fir_mul = mul;
Pico.snd.fm_fir_div = div;
- if (abs(mindiff) <= inrate/1000+1) break; // below error limit
+ if (abs(mindiff)*1000 <= inrate) break; // below error limit
}
}
printf("FM polyphase FIR ratio=%d/%d error=%.3f%%\n",
--
2.39.5