random ambient sound (pink/red noise)

ambient.pl

#!/usr/bin/perl
use strict;
use warnings;

use Math::FFTW;
use Audio::DSP;
use Time::HiRes qw(time);

my $amp = 0xffff;
my $len = 0xfff;
my $rate = 48000;
my $hard = .5; # 0=pink, 1=pink..red

my $start = time;
my $epsilon = 0.0001;

my $dsp = new Audio::DSP(
	buffer   => $len*2,
	channels => 1,
	format   => 16,
	rate     => $rate,
);
$dsp->init() or die $dsp->errstr();


sub min($$) { $_[0] < $_[1] ? $_[0] : $_[1] }
sub max($$) { $_[0] > $_[1] ? $_[0] : $_[1] }
sub clamp($$$) { $_[1] < $_[0] ? $_[0] : $_[1] > $_[2] ? $_[2] : $_[1] }
for (;;) {
	my $white = [map {rand($amp-1)-$amp/2} 0..$len];
	my $coeff = Math::FFTW::fftw_dft_real2complex_1d($white);
	my $n = scalar(@$coeff)/2;

	my $t = time;
	my $pow = (1+$hard/2)+($hard/2)*sin($t/20); # 1=pink, 2=red/brown
	my $nyquist = $rate/2;
	my $f = 1;
 	for (3..8) {
		$f *= .5+.5*abs(sin($t/$_));
 	}
	my $start_freq = 100 + 400 * $f;
	my $start_i = int(.99+$n*$start_freq/$nyquist);
	$start_freq = $start_i/$n*$nyquist;
	for(my $i=$start_i; $i<$n; $i++) {
		my $p = $i/($n-1);
		my $a = $p*$nyquist/$start_freq;
		my $b = log($a)/log(2);
		my $c = (2**$b)**$pow;
		$f = 1./$c;
		#print "".($p*$nyquist)." $start_freq $a $b $c : $f\n";
		$coeff->[$i*2+0] *= $f;
		$coeff->[$i*2+1] *= $f;
	}

 	for(my $i=1; $i<$n; $i++) {
		my $p = $i/($n-1);
 		my $f = 1;
 		for (3..8) {
 			$f *= .9+.1*sin($t/$_);
 		}
 		$coeff->[$i*2+0] *= $f;
 		$coeff->[$i*2+1] *= $f;
 	}

	my $pink = Math::FFTW::fftw_idft_complex2real_1d($coeff);

	$n = int(.99+$rate*0.001);
	for(my $i=0; $i<$n; $i++) {
		my $f = $i/$n;
		$pink->[ $i] *= $f;
		$pink->[-$i] *= $f;
	}

	$dsp->datacat(pack "s*", @$pink);
	$dsp->write() or die $dsp->errstr();

	my $delta = time - $start;
	my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday) = gmtime($delta);
	$sec += $delta - int($delta);

# 	my $n = scalar(@$coeff)/2;
#  	for(my $i=1; $i<$n; $i+=int($n/60)) {
# 		printf "%6d %s\n", $i/$n*$nyquist, '#' x int(log(1+sqrt(
# 				$coeff->[$i*2+0]**2 + 
# 				$coeff->[$i*2+1]**2 
# 			))*4);
# 	}

	$|=1; 
#	print "";
	printf "\r";
	printf "%dd ",    $yday if $yday;
	printf "%2dh ",   $hour if $hour||$yday;
	printf "%2dm ",   $min  if $min ||$hour||$yday;
	printf "%6.3fs ", $sec  if $sec ||$min ||$hour||$yday;


}