Code

Pink Noise Generator

September 26, 2011 Coded in Matlab

This code snippet generates "pink" noise by generating white noise and apply filter to turn it into pink noise.  See wiki article: http://en.wikipedia.org/wiki/Pink_noise

In general, pink noise is viewed as more natural than white noise and is used as test sources in many audio applications.

function out = create_pink_noise(Fs, Sec, Amp)

% Creates a pink noise signal and saves it as a wav file
%
% Usage: create_noise(Fs, Sec, Amp);
%
%        Fs is the desired sampling rate
%        Sec is the duration of the signal in seconds
%        Amp is the amplitude in dB of the signal (0dB to -144dB)
%
% Author: sparafucile17 06/14/02

%error trapping
if((Amp > 0) || (Amp < -144))
    error('Amplitude is not within the range of 0dB to -144dB');
end

%Create Whitenoise
white_noise = randn((Fs*Sec)+1,1);

%Apply weighted sum of first order filters to approximate a -10dB/decade
%filter.  This is Paul Kellet's "refined" method (a.k.a instrumentation
%grade)  It is accurate to within +/-0.05dB above 9.2Hz
b=zeros(7,1);
for i=1:((Fs*Sec)+1)
    b(1) = 0.99886 * b(1) + white_noise(i) * 0.0555179;
    b(2) = 0.99332 * b(2) + white_noise(i) * 0.0750759;
    b(3) = 0.96900 * b(3) + white_noise(i) * 0.1538520;
    b(4) = 0.86650 * b(4) + white_noise(i) * 0.3104856;
    b(5) = 0.55000 * b(5) + white_noise(i) * 0.5329522;
    b(6) = -0.7616 * b(6) - white_noise(i) * 0.0168980;
    pink_noise(i) = b(1) + b(2) + b(3) + b(4) + b(5) + b(6) + b(7) + white_noise(i) * 0.5362;
    b(7) = white_noise(i) * 0.115926; 
end

%Normalize to +/- 1
if(abs(min(pink_noise)) > max(pink_noise))  
    pink_noise = pink_noise / abs(min(pink_noise));
else
    pink_noise = pink_noise / max(pink_noise);
end

%Normalize to prevent positive saturation (We can't represent +1.0)
pink_noise = pink_noise /abs(((2^31)-1)/(2^31));

%Scale signal to match desired level
pink_noise = pink_noise * 10^(Amp/20);

%Output noise signal
out = pink_noise(1:end-1);

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