initial commit

1 files changed, 39 insertions, 0 deletions

diff --git a/freqnote.pl b/freqnote.pl
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index 0000000..eaf68ab
--- /dev/null
+++ b/freqnote.pl
@@ -0,0 +1,39 @@
+#!/usr/bin/perl -w
+
+# convert a frequency to a note name.
+# formula came from http://en.wikipedia.org/wiki/Note
+# p = 69 + 12 * log2(f/440)
+# ...where f is in Hz and p is the MIDI note number
+
+@notenames = (
+		'C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B'
+		);
+
+sub log2 {
+	return log($_[0])/log(2);
+}
+
+sub midi2note {
+	my $pitch = int(shift);
+	my $class = $notenames[$pitch % 12];
+	my $octave = int($pitch / 12) - 1;
+	return $class . $octave;
+}
+
+for(@ARGV) {
+	my $p = 69 + 12 * log2($_ / 440);
+	my $pitch = int($p);
+	my $cents = int(($p - $pitch) * 1000)/10;
+	if($cents > 50) {
+		$pitch++;
+		$cents = $cents - 100;
+	}
+	if($cents == 0) {
+		$cents = "";
+	} elsif($cents > 0) {
+		$cents = "+$cents" . "c";
+	} else {
+		$cents .= "c";
+	}
+	print $_ . "Hz = MIDI $pitch = " . midi2note($pitch) . " $cents\n";
+}