peyo22 · November 18, 2015 13:12 · Oct 10, 2015 · Oct 10, 2015 · Oct 10, 2015 · Oct 10, 2015
diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -12,8 +12,8 @@
 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 $depth_am      = 0.18;        # AM noise modulation index
+my $f_am          = 20;          # AM distortion frequency
+my $depth_am      = 0.18;        # AM distortion modulation index
 my $signal_gain   = dB(0);       # overall signal gain
 my $noise_gain    = dB(12);      # overall noise gain post-bandpass
 my $noise_shift   = 1.0;         # noise shift from harmonic (1 = none)

diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -97,6 +97,6 @@
 close $stream;
 
 sub dB       { 10 ** ($_[0] / 20); }
-sub pcmWord  { pack "s", round($_[0] * 0x7FFF); }
+sub pcmWord  { pack "s", round($_[0] * (2**16) / 2); }
 sub phaseInc { 2 * 3.14159 * $_[0] / $fs; }
 sub round    { $_[0] >= 0 ? int($_[0] + .5) : int($_[0] - .5); }
diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -35,6 +35,8 @@
 
 open my $stream, '|-', 'sox -t .s16 -c 1 -r ' . $fs . ' - ' . $outfile
   or die $!;
+
+binmode($stream) or die $!;
 
 print $stream pcmWord(0) x ($padding * $fs);
 
@@ -45,14 +47,14 @@
     $f = $fc - $riseband + ($t/$risetime * $riseband);
     $vol = $t/$risetime;
     $harmonics[0] = ($t < $risetime * .66 ? 0 :
-      ($t-$risetime * .66) / ($risetime * .66));
+      ($t-$risetime * .66) / ($risetime * .33));
 
   } elsif ($t > $risetime + $dur) {
     # release
     $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) / ($risetime * .33));
+      dB(0) - ($t-$dur-$risetime) / ($risetime * .33));
 
   } else {
 
@@ -95,5 +97,6 @@
 close $stream;
 
 sub dB       { 10 ** ($_[0] / 20); }
-sub pcmWord  { pack "s", $_[0] * 0x7FFF; }
-sub phaseInc { 2 * 3.14159 * $_[0] / $fs; }
+sub pcmWord  { pack "s", round($_[0] * 0x7FFF); }
+sub phaseInc { 2 * 3.14159 * $_[0] / $fs; }
+sub round    { $_[0] >= 0 ? int($_[0] + .5) : int($_[0] - .5); }
diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -18,7 +18,7 @@
 my $noise_gain    = dB(12);      # overall noise gain post-bandpass
 my $noise_shift   = 1.0;         # noise shift from harmonic (1 = none)
 my $lp_alfa_fm    = 0.004;       # signal pre-fm lopass bandwidth
-my $lp_alfa_noise = 0.009;       # noise bandpass bandwidth
+my $bp_alfa_noise = 0.009;       # noise bandpass bandwidth
 my $fshift        = 0.077 * $fc; # FSK shift
 
 # relative harmonic powers
@@ -72,7 +72,7 @@
   $prev_f     = $f_filtered;
 
   my $noise = rand() - .5;
-  my $noise_filtered = $lp_alfa_noise * $noise + (1 - $lp_alfa_noise) *
+  my $noise_filtered = $bp_alfa_noise * $noise + (1 - $bp_alfa_noise) *
     $prev_noise;
   $prev_noise = $noise_filtered;
 

diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -41,14 +41,14 @@
 for (my $t = 0; $t < $risetime * 2 + $dur; $t += 1/$fs) {
 
   if ($t < $risetime) {
-
+    # attack
     $f = $fc - $riseband + ($t/$risetime * $riseband);
     $vol = $t/$risetime;
     $harmonics[0] = ($t < $risetime * .66 ? 0 :
       ($t-$risetime * .66) / ($risetime * .66));
 
   } elsif ($t > $risetime + $dur) {
-
+    # release
     $f = $fc - ($t-$dur-$risetime) / $risetime * $riseband;
     $vol = dB(0) - ($t-$dur-$risetime) / $risetime;
     $harmonics[0] = ($t-$dur-$risetime > $risetime * .33 ? 0 :

diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -1,10 +1,10 @@
 # windytan's pea whistle encoder
 # http://www.windytan.com/2015/10/pea-whistle-steganography.html
-
 use warnings;
 use strict;
 
 my $data          = $ARGV[0] // "OHAI!";
+my $outfile       = "whistle.wav";
 
 my $fs            = 44100;       # sample rate
 my $fc            = 2600;        # whistle pitch
@@ -33,7 +33,7 @@
 my $f, my $f_filtered, my $vol;
 my $ph_am, my $ph_fm;
 
-open my $stream, '|-', 'sox -t .s16 -c 1 -r ' . $fs . ' - whistle.wav'
+open my $stream, '|-', 'sox -t .s16 -c 1 -r ' . $fs . ' - ' . $outfile
   or die $!;
 
 print $stream pcmWord(0) x ($padding * $fs);

diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -1,25 +1,25 @@
-# Oona Räisänen's pea whistle encoder
+# windytan'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
+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 $depth_am      = 0.18;        # AM noise modulation index
+my $signal_gain   = dB(0);       # overall signal gain
+my $noise_gain    = dB(12);      # overall noise gain post-bandpass
+my $noise_shift   = 1.0;         # noise shift from harmonic (1 = none)
+my $lp_alfa_fm    = 0.004;       # signal 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));
@@ -30,15 +30,15 @@
 
 my $prev_noise = 0;
 my $prev_f = $fc - $riseband;
-my $f, my $f_filt, my $vol;
+my $f, my $f_filtered, my $vol;
 my $ph_am, my $ph_fm;
 
-open my $stream, '|-', "sox -t .s16 -c 1 -r $fs - whistle.wav"
+open my $stream, '|-', 'sox -t .s16 -c 1 -r ' . $fs . ' - whistle.wav'
   or die $!;
 
-print $stream pack("s", 0) x ($padding * $fs);
+print $stream pcmWord(0) x ($padding * $fs);
 
-for (my $t = 0; $t < $risetime*2 + $dur; $t += 1/$fs) {
+for (my $t = 0; $t < $risetime * 2 + $dur; $t += 1/$fs) {
 
   if ($t < $risetime) {
 
@@ -68,30 +68,32 @@
     $vol = dB(0);
   }
 
-  $f_filt = $lp_alfa_fm * $f + (1 - $lp_alfa_fm) * $prev_f;
-  $prev_f = $f_filt;
+  $f_filtered = $lp_alfa_fm * $f + (1 - $lp_alfa_fm) * $prev_f;
+  $prev_f     = $f_filtered;
 
   my $noise = rand() - .5;
-  my $noise_filt = $lp_alfa_noise * $noise + (1 - $lp_alfa_noise) *
+  my $noise_filtered = $lp_alfa_noise * $noise + (1 - $lp_alfa_noise) *
     $prev_noise;
-  $prev_noise = $noise_filt;
+  $prev_noise = $noise_filtered;
 
-  $ph_fm += 2 * 3.14159 * $f_filt / $fs;
-  $ph_am += 2 * 3.14159 * $f_am / $fs;
+  $ph_fm += phaseInc($f_filtered);
+  $ph_am += phaseInc($f_am);
 
   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] *
+    $mix += $signal_gain * $sig * (dB(0) + $depth_am * cos($ph_am));
+    $mix += $noise_gain * $noise_filtered * $noise_harmonics[$n] *
       cos(($n + 1) * ($ph_fm * $noise_shift));
   }
 
-  print $stream pack("s", dB(-14) * $vol * $mix * 0x7FFF);
+  print $stream pcmWord(dB(-14) * $vol * $mix);
 }
 
-print $stream pack("s", 0) x ($padding * $fs);
+print $stream pcmWord(0) x ($padding * $fs);
 
 close $stream;
 
-sub dB { 10 ** ($_[0] / 20); }
+sub dB       { 10 ** ($_[0] / 20); }
+sub pcmWord  { pack "s", $_[0] * 0x7FFF; }
+sub phaseInc { 2 * 3.14159 * $_[0] / $fs; }
diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -13,9 +13,9 @@
 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 modulation index
+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
+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

diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -11,19 +11,19 @@
 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
+my $padding     = 0.5;         # silence before and after, sec
 my $f_am        = 20;          # AM noise frequency
-my $vol_am      = 0.18;        # amplitude thereof
-my $sig_vol     = 1;           # overall signal gain
-my $noise_vol   = 4;           # overall noise gain
-my $noise_shift = 1.0;         # from harmonic center (1 = none)
+my $vol_am      = 0.18;        # AM modulation index
+my $sig_vol     = dB(0);       # overall signal gain
+my $noise_vol   = dB(12);      # overall noise gain
+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 = (1, 0.141, 0.022, 0.0398, 0.0282, 0.0063);
-my @noise_harmonics = (1, 0.9, 0.8, 0.7, 0.6, 0.5);
+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 / $bps;
@@ -50,22 +50,22 @@
   } elsif ($t > $risetime + $dur) {
 
     $f = $fc - ($t-$dur-$risetime) / $risetime * $riseband;
-    $vol = 1 - ($t-$dur-$risetime) / $risetime;
+    $vol = dB(0) - ($t-$dur-$risetime) / $risetime;
     $harmonics[0] = ($t-$dur-$risetime > $risetime * .33 ? 0 :
-      1 - (($t-$dur-$risetime) * .33) / ($risetime * .33));
+      dB(0) - (($t-$dur-$risetime) * .33) / ($risetime * .33));
 
   } else {
 
     $f = $fc;
-    $harmonics[0] = 1;
+    $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 = 1;
+    $vol = dB(0);
   }
 
   $f_filt = $lp_alfa_fm * $f + (1 - $lp_alfa_fm) * $prev_f;
@@ -87,9 +87,11 @@
       cos(($n + 1) * ($ph_fm * $noise_shift));
   }
 
-  print $stream pack("s", 0.2 * $vol * $mix * 0x7FFF);
+  print $stream pack("s", dB(-14) * $vol * $mix * 0x7FFF);
 }
 
 print $stream pack("s", 0) x ($padding * $fs);
 
-close $stream;
+close $stream;
+
+sub dB { 10 ** ($_[0] / 20); }
diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -18,7 +18,7 @@
 my $noise_vol   = 4;           # overall noise gain
 my $noise_shift = 1.0;         # from harmonic center (1 = none)
 my $lp_alfa_fm  = 0.004;       # pre-fm lopass bandwidth
-my $lp_alfa_noise = 0.009;     # noise lopass bandwidth
+my $lp_alfa_noise = 0.009;     # noise bandpass bandwidth
 my $fshift      = 0.077 * $fc; # FSK shift
 
 # relative harmonic powers

diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -6,26 +6,28 @@
 
 my $data        = $ARGV[0] // "OHAI!";
 
-my $fs          = 44100;
-my $fc          = 2600;
-my $bps         = 100;
-my $risetime    = 0.09;
-my $padding     = 0.5;
-my $f_am        = 20;
-my $vol_am      = 0.18;
-my $sig_vol     = 1;
-my $noise_vol   = 4;
-my $noise_shift = 1.0;
-my $lp_alfa_fm  = 0.004;
-my $lp_alfa_noise = 0.009;
-my $fshift      = 0.0769 * $fc;
-my $riseband    = 0.7 * $fc;
+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
+my $f_am        = 20;          # AM noise frequency
+my $vol_am      = 0.18;        # amplitude thereof
+my $sig_vol     = 1;           # overall signal gain
+my $noise_vol   = 4;           # overall noise gain
+my $noise_shift = 1.0;         # from harmonic center (1 = none)
+my $lp_alfa_fm  = 0.004;       # pre-fm lopass bandwidth
+my $lp_alfa_noise = 0.009;     # noise lopass bandwidth
+my $fshift      = 0.077 * $fc; # FSK shift
+
+# relative harmonic powers
+my @harmonics = (1, 0.141, 0.022, 0.0398, 0.0282, 0.0063);
+my @noise_harmonics = (1, 0.9, 0.8, 0.7, 0.6, 0.5);
+
 $data           = "\xAA\xA7" . pack("C", length($data)) . $data;
 my $dur         = length($data) * 8 / $bps;
 
-my @harmonics = (1, 0.141, 0.022, 0.0398, 0.0282, 0.0063);
-my @harmonics_noise = (1, 0.9, 0.8, 0.7, 0.6, 0.5);
-
 my $prev_noise = 0;
 my $prev_f = $fc - $riseband;
 my $f, my $f_filt, my $vol;
@@ -81,7 +83,7 @@
   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 * $harmonics_noise[$n] *
+    $mix += $noise_vol * $noise_filt * $noise_harmonics[$n] *
       cos(($n + 1) * ($ph_fm * $noise_shift));
   }
 

diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -26,17 +26,16 @@
 my @harmonics = (1, 0.141, 0.022, 0.0398, 0.0282, 0.0063);
 my @harmonics_noise = (1, 0.9, 0.8, 0.7, 0.6, 0.5);
 
-open my $stream, '|-', "sox -t .s16 -c 1 -r $fs - whistle.wav"
-  or die $!;
-
-print $stream pack("s", 0) x ($padding * $fs);
-
-my $t = 0;
 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) {
@@ -58,9 +57,9 @@
     $f = $fc;
     $harmonics[0] = 1;
 
-    my $bitind = int(($t - $risetime) * $bps);
-    my $byte   = substr($data, int($bitind / 8), 1);
-    my $bit    = ((ord($byte) >> ($bitind % 8)) & 1);
+    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;
 

diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -32,12 +32,12 @@
 print $stream pack("s", 0) x ($padding * $fs);
 
 my $t = 0;
-my $prevy = 0;
+my $prev_noise = 0;
 my $prev_f = $fc - $riseband;
 my $f, my $f_filt, my $vol;
 my $ph_am, my $ph_fm;
-for (0.. ($risetime+$dur+$risetime) * $fs) {
-  $t += 1/$fs;
+
+for (my $t = 0; $t < $risetime*2 + $dur; $t += 1/$fs) {
 
   if ($t < $risetime) {
 
@@ -59,33 +59,34 @@
     $harmonics[0] = 1;
 
     my $bitind = int(($t - $risetime) * $bps);
-    my $byte   = substr($data, int($bitind / 8),1);
+    my $byte   = substr($data, int($bitind / 8), 1);
     my $bit    = ((ord($byte) >> ($bitind % 8)) & 1);
 
-    $f = ($bit-.5)*$fshift + $fc;
+    $f = ($bit - .5) * $fshift + $fc;
 
     $vol = 1;
   }
 
-  $f_filt = $lp_alfa_fm * $f + (1-$lp_alfa_fm) * $prev_f;
+  $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) * $prevy;
-  $prevy = $noise_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 $total = 0;
-  for (0..$#harmonics) {
-    my $s = $harmonics[$_] * cos(($_+1) * $ph_fm);
-    $total += $sig_vol * $s * (1 + $vol_am * cos($ph_am));
-    $total += $noise_vol * $noise_filt * $harmonics_noise[$_] *
-      cos(($_+1) * ($ph_fm * $noise_shift));
+  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 * $harmonics_noise[$n] *
+      cos(($n + 1) * ($ph_fm * $noise_shift));
   }
 
-  print $stream pack("s", 0.2 * $vol * $total * 0x7FFF);
+  print $stream pack("s", 0.2 * $vol * $mix * 0x7FFF);
 }
 
 print $stream pack("s", 0) x ($padding * $fs);

diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -1,9 +1,12 @@
+# 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          = 96000;
+my $fs          = 44100;
 my $fc          = 2600;
 my $bps         = 100;
 my $risetime    = 0.09;
@@ -76,10 +79,10 @@
 
   my $total = 0;
   for (0..$#harmonics) {
-    my $s = $harmonics[$_] * sin(($_+1) * $ph_fm);
-    $total += $sig_vol * $s * (1 + $vol_am*sin($ph_am));
+    my $s = $harmonics[$_] * cos(($_+1) * $ph_fm);
+    $total += $sig_vol * $s * (1 + $vol_am * cos($ph_am));
     $total += $noise_vol * $noise_filt * $harmonics_noise[$_] *
-      sin(($_+1) * ($ph_fm * $noise_shift));
+      cos(($_+1) * ($ph_fm * $noise_shift));
   }
 
   print $stream pack("s", 0.2 * $vol * $total * 0x7FFF);

diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -17,7 +17,7 @@
 my $lp_alfa_noise = 0.009;
 my $fshift      = 0.0769 * $fc;
 my $riseband    = 0.7 * $fc;
-$data           = "\xAA\xA7".chr(length($data)).$data;
+$data           = "\xAA\xA7" . pack("C", length($data)) . $data;
 my $dur         = length($data) * 8 / $bps;
 
 my @harmonics = (1, 0.141, 0.022, 0.0398, 0.0282, 0.0063);

diff --git a/whistle-encode.pl b/whistle-encode.pl
@@ -0,0 +1,90 @@
+use warnings;
+use strict;
+
+my $data        = $ARGV[0] // "OHAI!";
+
+my $fs          = 96000;
+my $fc          = 2600;
+my $bps         = 100;
+my $risetime    = 0.09;
+my $padding     = 0.5;
+my $f_am        = 20;
+my $vol_am      = 0.18;
+my $sig_vol     = 1;
+my $noise_vol   = 4;
+my $noise_shift = 1.0;
+my $lp_alfa_fm  = 0.004;
+my $lp_alfa_noise = 0.009;
+my $fshift      = 0.0769 * $fc;
+my $riseband    = 0.7 * $fc;
+$data           = "\xAA\xA7".chr(length($data)).$data;
+my $dur         = length($data) * 8 / $bps;
+
+my @harmonics = (1, 0.141, 0.022, 0.0398, 0.0282, 0.0063);
+my @harmonics_noise = (1, 0.9, 0.8, 0.7, 0.6, 0.5);
+
+open my $stream, '|-', "sox -t .s16 -c 1 -r $fs - whistle.wav"
+  or die $!;
+
+print $stream pack("s", 0) x ($padding * $fs);
+
+my $t = 0;
+my $prevy = 0;
+my $prev_f = $fc - $riseband;
+my $f, my $f_filt, my $vol;
+my $ph_am, my $ph_fm;
+for (0.. ($risetime+$dur+$risetime) * $fs) {
+  $t += 1/$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;
+    $vol = 1 - ($t-$dur-$risetime) / $risetime;
+    $harmonics[0] = ($t-$dur-$risetime > $risetime * .33 ? 0 :
+      1 - (($t-$dur-$risetime) * .33) / ($risetime * .33));
+
+  } else {
+
+    $f = $fc;
+    $harmonics[0] = 1;
+
+    my $bitind = int(($t - $risetime) * $bps);
+    my $byte   = substr($data, int($bitind / 8),1);
+    my $bit    = ((ord($byte) >> ($bitind % 8)) & 1);
+
+    $f = ($bit-.5)*$fshift + $fc;
+
+    $vol = 1;
+  }
+
+  $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) * $prevy;
+  $prevy = $noise_filt;
+
+  $ph_fm += 2 * 3.14159 * $f_filt / $fs;
+  $ph_am += 2 * 3.14159 * $f_am / $fs;
+
+  my $total = 0;
+  for (0..$#harmonics) {
+    my $s = $harmonics[$_] * sin(($_+1) * $ph_fm);
+    $total += $sig_vol * $s * (1 + $vol_am*sin($ph_am));
+    $total += $noise_vol * $noise_filt * $harmonics_noise[$_] *
+      sin(($_+1) * ($ph_fm * $noise_shift));
+  }
+
+  print $stream pack("s", 0.2 * $vol * $total * 0x7FFF);
+}
+
+print $stream pack("s", 0) x ($padding * $fs);
+
+close $stream;
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