Demonstration of Nyquist's Theorem.

nyquist.pl

use strict;
use warnings;
use Audio::Wav;
use Math::Complex;

use constant TWO_PI => pi() * 2;

my $wav = Audio::Wav->new();
my $sample_rate = 44100;
my $bits_sample = 16;

write_out( 'nyquist_good.wav', 8000, 2 );
write_out( 'nyquist_bad.wav', 36000, 2 );

sub write_out {
   my $filename = shift;
   my $write = $wav->write($filename, {
      bits_sample => $bits_sample,
      sample_rate => $sample_rate,
      channels    => 1,
   });
   add_sine( $write, @_ );
   $write->finish();
}

sub add_sine {
   my ($write,$hz,$length) = @_;
   my $max_no = (2 ** $bits_sample) / 2;
   $length   *= $sample_rate;

   for my $pos (0..$length) {
       my $time = ($pos / $sample_rate) * $hz;
       my $val  = sin(TWO_PI * $time);
       my $samp = $val * $max_no;
       $write->write($samp);
   }
}