The Audio::DSP module allows you to write generated tones to the soundcard. The PDL::Audio module generates realistic bird calls from data. :-) The script below, generates a series of numbers, that is fed to the soundcard, play with it for different tones.

#!/usr/bin/perl
use warnings;
use strict;
use Audio::DSP;
$| = 1;

my $sample_rate = 22050;   #44100 gives best sound, but highest cpu
                           #8000 works 
my $channels = 1;
my $format = AFMT_S16_LE;  #8 bit won't work on SBLive
my $buffer = 4096;

my $dsp = new Audio::DSP(buffer   => $buffer,
                      channels => $channels,
                      format   => $format,
                      rate     => $sample_rate);
$dsp->init() || die $dsp->errstr();

############################################################
my $freq_adj = .1;
my $vol = .5;
my $toggle = 1;

while(1){
  make_tone($freq_adj, $vol);

  if(($freq_adj > 4) or ($freq_adj < .1)){ $toggle *= -1;}

  $freq_adj += ($toggle * .001); #higher increment numbers are slower
                                 #0 is pure tone
}

sub make_tone {
     my $rad = 0;
     my ($freq_adj, $vol) = @_;
     while ( $rad < 6.283 ){
         $rad +=  $freq_adj;     
     my $raw = ($vol*32768) * sin($rad);    #max times
       my $num = pack( 'V', $raw  ); 
           $dsp->dwrite($num);
        }
}
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