-
-
Save peyo22/3e44ec95d4ecc2f2da9f to your computer and use it in GitHub Desktop.
whistle encoder
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| # Oona Räisänen's pea whistle encoder | |
| # http://www.windytan.com/2015/10/pea-whistle-steganography.html | |
| use warnings; | |
| use strict; | |
| my $data = $ARGV[0] // "OHAI!"; | |
| my $fs = 44100; # sample rate | |
| my $fc = 2600; # whistle pitch | |
| my $bps = 100; # data speed | |
| my $risetime = 0.09; # rise/fall slide duration | |
| my $riseband = 0.7 * $fc; # bandwidth thereof | |
| my $padding = 0.5; # silence before and after, sec | |
| my $f_am = 20; # AM noise frequency | |
| my $vol_am = 0.18; # AM noise modulation index | |
| my $sig_vol = dB(0); # overall signal gain | |
| my $noise_vol = dB(12); # overall noise gain after bandpass | |
| my $noise_shift = 1.0; # noise shift from harmonic (1 = none) | |
| my $lp_alfa_fm = 0.004; # pre-fm lopass bandwidth | |
| my $lp_alfa_noise = 0.009; # noise bandpass bandwidth | |
| my $fshift = 0.077 * $fc; # FSK shift | |
| # relative harmonic powers | |
| my @harmonics = (dB(0), dB(-17), dB(-33), dB(-28), dB(-31), dB(-44)); | |
| my @noise_harmonics = (dB(0), dB(-1), dB(-2), dB(-3), dB(-4), dB(-6)); | |
| $data = "\xAA\xA7" . pack("C", length($data)) . $data; | |
| my $dur = length($data) * 8 / $bps; | |
| my $prev_noise = 0; | |
| my $prev_f = $fc - $riseband; | |
| my $f, my $f_filt, my $vol; | |
| my $ph_am, my $ph_fm; | |
| open my $stream, '|-', "sox -t .s16 -c 1 -r $fs - whistle.wav" | |
| or die $!; | |
| print $stream pack("s", 0) x ($padding * $fs); | |
| for (my $t = 0; $t < $risetime*2 + $dur; $t += 1/$fs) { | |
| if ($t < $risetime) { | |
| $f = $fc - $riseband + ($t/$risetime * $riseband); | |
| $vol = $t/$risetime; | |
| $harmonics[0] = ($t < $risetime * .66 ? 0 : | |
| ($t-$risetime * .66) / ($risetime * .66)); | |
| } elsif ($t > $risetime + $dur) { | |
| $f = $fc - ($t-$dur-$risetime) / $risetime * $riseband; | |
| $vol = dB(0) - ($t-$dur-$risetime) / $risetime; | |
| $harmonics[0] = ($t-$dur-$risetime > $risetime * .33 ? 0 : | |
| dB(0) - (($t-$dur-$risetime) * .33) / ($risetime * .33)); | |
| } else { | |
| $f = $fc; | |
| $harmonics[0] = dB(0); | |
| my $bit_i = int(($t - $risetime) * $bps); | |
| my $byte = substr($data, int($bit_i / 8), 1); | |
| my $bit = ((unpack("C", $byte) >> ($bit_i % 8)) & 1); | |
| $f = ($bit - .5) * $fshift + $fc; | |
| $vol = dB(0); | |
| } | |
| $f_filt = $lp_alfa_fm * $f + (1 - $lp_alfa_fm) * $prev_f; | |
| $prev_f = $f_filt; | |
| my $noise = rand() - .5; | |
| my $noise_filt = $lp_alfa_noise * $noise + (1 - $lp_alfa_noise) * | |
| $prev_noise; | |
| $prev_noise = $noise_filt; | |
| $ph_fm += 2 * 3.14159 * $f_filt / $fs; | |
| $ph_am += 2 * 3.14159 * $f_am / $fs; | |
| my $mix = 0; | |
| for my $n (0..$#harmonics) { | |
| my $sig = $harmonics[$n] * cos(($n + 1) * $ph_fm); | |
| $mix += $sig_vol * $sig * (1 + $vol_am * cos($ph_am)); | |
| $mix += $noise_vol * $noise_filt * $noise_harmonics[$n] * | |
| cos(($n + 1) * ($ph_fm * $noise_shift)); | |
| } | |
| print $stream pack("s", dB(-14) * $vol * $mix * 0x7FFF); | |
| } | |
| print $stream pack("s", 0) x ($padding * $fs); | |
| close $stream; | |
| sub dB { 10 ** ($_[0] / 20); } |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment