Make parameters adjustable

Adjusting parameters can result in more files being extractable

1 files changed, 15 insertions, 19 deletions

diff --git a/mfmdecode.c b/mfmdecode.c
index 6eeec0f..7cee0e4 100644
--- a/mfmdecode.c
+++ b/mfmdecode.c
@@ -1,14 +1,10 @@
 /*
- * Decode ABC80 cassette files (by H. Peter Anvin, 
- * modified by Mikael O. Bonnier 2012-07-23)
+ * Decode ABC80 cassette files
  *
- * Convert to samples Hz single channel 16-bit with appropriate endianness
+ * Convert to 44100 Hz single channel 16-bit with appropriate endianness
  * and normalized gain first:
  *
  * sox muzak.wav --endian little -c 1 -s muzak.raw
- * mfmdecode muzak.raw 44100 5300
- *
- * This program doesn't work with 96 kHz.
  */
 
 #include <stdio.h>
@@ -17,10 +13,7 @@
 #include <math.h>
 #include <inttypes.h>
 
-static unsigned int thresh; /* threshold e.g. 5300 */
-static unsigned int samples; /* sample frequency in Hz e.g. 44100 or 96000
-*/
-static unsigned int xtime;	/* samples/baud */
+static unsigned int xtime;
 
 static const char my_tolower[256] =
   "\000\001\002\003\004\005\006\007\010\011\012\013\014\015\016\017"
@@ -76,12 +69,12 @@ static void output_block(uint8_t *buf, uint8_t *csum)
 		csum1 = 0x03;		/* Checksum includes ETX */
 		for (i = 0; i < 256; i++)
 			csum1 += buf[i];
-
+		
 		if (csum1 == csum2) {
 			if (!memcmp(buf, "\xff\xff\xff", 3)) {
 				if (f)
 					fclose(f);
-
+				
 				unmangle_filename(filename, buf+3);
 				f = fopen(filename, "wb");
 				if (!f) {
@@ -224,24 +217,27 @@ static void process_flank(unsigned int time)
 
 int main(int argc, char *argv[])
 {
+	unsigned int frequency;
 	FILE *f;
 	int16_t samp, osamp;
-	double v;
+	double v, k, cutoff, thresh;
 	unsigned int state;
 	unsigned int time, ptime;
-	double k;
 
 	f = fopen(argv[1], "rb");
-	sscanf(argv[2], "%u", &samples);
- 	sscanf(argv[3], "%u", &thresh);
-    xtime = samples/700;
-	k = exp(-10000.0/samples);
+	
+	frequency = (argc > 2) ? strtoul(argv[2], NULL, 0) : 44100;
+	thresh = (argc > 3) ? atof(argv[3]) : 5300.0;
+	cutoff = (argc > 4) ? atof(argv[4]) : 0.0;
+	
+	k = exp(-cutoff/frequency);
+	xtime = frequency/700;	/* Samples per baud */
+
 	state = time = ptime = 0;
 	samp = osamp = 0;
 	v = 0.0;
 
 	while (fread(&samp, 1, 2, f) == 2) {
-
 		/* Emulate high pass filter in ABC80 */
 		v = (v * k) + (samp - osamp);
 		osamp = samp;