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#!/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";
}
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