commit b39d78e207dcbebee9ed48dbc0c3be62143a7757
parent 2f656be8e0b89051a4c2b3ffe4cc4c4e5934731e
Author: Antoine Amarilli <a3nm@a3nm.net>
Date: Wed, 29 Oct 2014 20:05:10 +0100
+a2freq
Diffstat:
| a2freq.c | | | 146 | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ |
1 file changed, 146 insertions(+), 0 deletions(-)
diff --git a/a2freq.c b/a2freq.c
@@ -0,0 +1,146 @@
+/* a2freq - convert MIDI note numbers or scientific pitch notations to frequencies */
+/* by Antoine Amarilli (2011) */
+/* licence: public domain */
+/* compilation: cc -lm -o a2freq a2freq.c */
+
+#include <stdio.h>
+#include <math.h>
+#include <ctype.h>
+
+#define E_ARGS 1
+#define E_PARSE 2
+
+int atoi(const char *nptr);
+
+
+float key2freq(int n)
+{
+ /* Return frequency of midi note number n, inspired by the "Piano key
+ * frequencies" article on wikipedia */
+
+ return 440*pow(2, ((float) (n - 69))/12);
+}
+
+
+int name2num(char name)
+{
+ /* Return note number adjustment for upper case scientific pitch
+ * notation note name name. Return <0 on error. */
+
+ switch(name)
+ {
+ case 'C':
+ return 0;
+ case 'D':
+ return 2;
+ case 'E':
+ return 4;
+ case 'F':
+ return 5;
+ case 'G':
+ return 7;
+ case 'A':
+ return 9;
+ case 'B':
+ return 11;
+ default:
+ return -1;
+ }
+}
+
+
+int accid2num(char accid)
+{
+ /* Return note number adjustment for scientific pitch notation note
+ * accidental. Return 0 on error. */
+
+ switch (accid) {
+ case 'b':
+ return -1;
+ case '#':
+ return 1;
+ default:
+ return 0;
+ }
+}
+
+
+int note2num(int octave, int note)
+{
+ /* Return MIDI note number for octave and note. */
+
+ return (octave + 1)*12 + note;
+}
+
+
+float pitch2freq(char* a)
+{
+ /* Return frequency of scientific pitch notation note a, by converting
+ * it to a key number and using key2freq. Return <0 on parse error. */
+
+ // octavepos position where octave indication is expected
+ int note, octave = 4, accid, octavepos = 1;
+
+ /* parse note name */
+ if (!a[0]) return -1;
+ note = name2num(toupper(a[0]));
+ if (note < 0) return note;
+
+ /* parse accidental */
+ if (a[octavepos] && !isdigit(a[octavepos])) {
+ accid = accid2num(a[octavepos]);
+ if (!accid) return -1;
+ note += accid;
+ octavepos++;
+ }
+
+ /* parse octave */
+ return key2freq(!a[octavepos]?
+ note2num(octave, note):
+ note2num(atoi(a + octavepos), note));
+}
+
+
+float do_one(char* a)
+{
+ int result;
+
+ if ((result = atoi(a)))
+ return key2freq(result);
+ else return pitch2freq(a);
+}
+
+
+int main(int argc, char** argv)
+{
+ int i;
+ double result;
+
+ if (argc <= 1) {
+ fprintf(stderr,
+ "Usage: %s [NOTE]...\n", argv[0]);
+ fprintf(stderr,
+ "Convert MIDI note numbers or scientific pitch notations to "
+ "frequencies.\n");
+ fprintf(stderr,
+ "NOTE is either a MIDI note number or a key in scientific pitch "
+ "notation.\n");
+ fprintf(stderr,
+ "Scientific pitch notation examples: \"A4\", \"C#2\", " "\"Bb6\"\n");
+ return E_ARGS;
+ }
+
+ for (i=1; i<argc; i++)
+ {
+ result = do_one(argv[i]);
+ if (result >= 0)
+ printf("%f\n", result);
+ else {
+ fprintf(stderr, "a2freq: cannot parse %s\n", argv[i]);
+ return E_PARSE;
+ }
+ }
+
+ return 0;
+}
+
