Difference between revisions of "Ripple Sounds"
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| Line 25: | Line 25: | ||
| the ripple density in the frequency domain | | the ripple density in the frequency domain | ||
|- | |- | ||
| − | | | + | | rippleType |
| determines if the ripple is ascending or descending | | determines if the ripple is ascending or descending | ||
|- | |- | ||
| − | | | + | | modulationDepth |
| half the amplitude of the modulation | | half the amplitude of the modulation | ||
|} | |} | ||
| − | The variables that are sin modulated | + | The variables that are sin modulated are denoted by the prefix 'sin_', the cos modulated by '_cos'. |
| − | The variables in the time domain are denoted by '_time' | + | The variables in the time domain are denoted by the suffix '_time' and variables in the frequency domain by the suffix '_freq'. |
<pre> | <pre> | ||
% Generate array with pink noise | % Generate array with pink noise | ||
| − | + | pinkNoise_time = pinknoise(length(t)); | |
% Create modulation functions for time domain (velocity modulation) | % Create modulation functions for time domain (velocity modulation) | ||
| Line 53: | Line 53: | ||
% Apply time modulation to pink noise in the time domain | % Apply time modulation to pink noise in the time domain | ||
| − | + | sin_modulatedNoise_time = sin_modulation_time .* pinkNoise_time; | |
| − | + | cos_modulatedNoise_time = cos_modulation_time .* pinkNoise_time; | |
% Perform fft to convert the signals to the frequency domain | % Perform fft to convert the signals to the frequency domain | ||
| − | + | sin_modulatedNoise_freq = fft(sin_modulatedNoise_time); | |
| − | + | cos_modulatedNoise_freq = fft(cos_modulatedNoise_time); | |
% Apply frequency modulation in the frequency domain | % Apply frequency modulation in the frequency domain | ||
| − | + | sin_rippledNoise_freq = sin_modulation_freq .* sin_modulatedNoise_freq; | |
| − | + | cos_rippledNoise_freq = cos_modulation_freq .* cos_modulatedNoise_freq; | |
% Perform ifft to get rippled noise in the time domain | % Perform ifft to get rippled noise in the time domain | ||
| − | + | sin_rippledNoise_time = ifft(sin_rippledNoise_freq, 'symmetric'); | |
| − | + | cos_rippledNoise_time = ifft(cos_rippledNoise_freq, 'symmetric'); | |
% Determine the ripple type (ascending vs. descending) | % Determine the ripple type (ascending vs. descending) | ||
| − | switch | + | switch rippleType |
case 'ascending' | case 'ascending' | ||
| − | + | combinedRippledNoise_time = sin_rippledNoise_time + cos_rippledNoise_time; | |
case 'descending' | case 'descending' | ||
| − | + | combinedRippledNoise_time = sin_rippledNoise_time - cos_rippledNoise_time; | |
end | end | ||
% Calculate the final rippled stimulus in the time domain | % Calculate the final rippled stimulus in the time domain | ||
| − | + | rippledStimulus_time = pinkNoise_time + modulationDepth * combinedRippledNoise_time; | |
</pre> | </pre> | ||
Revision as of 11:05, 16 August 2024
Introduction
%todo
FFT-iFFT method
Below is an example of an implementation in matlab. It is based on a broadband signal consisting of pink noise. The input parameters are:
| Term | Description |
|---|---|
| t | time domain array in seconds |
| octaves | frequency domain array in octaves |
| ripples_per_sec | the ripple velocity in the time domain |
| phi | a phase that can be added to the time modulation |
| ripples_per_octave | the ripple density in the frequency domain |
| rippleType | determines if the ripple is ascending or descending |
| modulationDepth | half the amplitude of the modulation |
The variables that are sin modulated are denoted by the prefix 'sin_', the cos modulated by '_cos'.
The variables in the time domain are denoted by the suffix '_time' and variables in the frequency domain by the suffix '_freq'.
% Generate array with pink noise
pinkNoise_time = pinknoise(length(t));
% Create modulation functions for time domain (velocity modulation)
sin_modulation_time = sin(2 * pi * ripples_per_sec * t + phi);
cos_modulation_time = cos(2 * pi * ripples_per_sec * t + phi);
% Create modulation functions for frequency domain (density modulation)
sin_modulation_freq = sin(2 * pi * ripples_per_octave * octaves);
cos_modulation_freq = cos(2 * pi * ripples_per_octave * octaves);
% Mirror the frequency modulation components for ifft compatibility
sin_modulation_freq = [sin_modulation_freq, fliplr(sin_modulation_freq)];
cos_modulation_freq = [cos_modulation_freq, fliplr(cos_modulation_freq)];
% Apply time modulation to pink noise in the time domain
sin_modulatedNoise_time = sin_modulation_time .* pinkNoise_time;
cos_modulatedNoise_time = cos_modulation_time .* pinkNoise_time;
% Perform fft to convert the signals to the frequency domain
sin_modulatedNoise_freq = fft(sin_modulatedNoise_time);
cos_modulatedNoise_freq = fft(cos_modulatedNoise_time);
% Apply frequency modulation in the frequency domain
sin_rippledNoise_freq = sin_modulation_freq .* sin_modulatedNoise_freq;
cos_rippledNoise_freq = cos_modulation_freq .* cos_modulatedNoise_freq;
% Perform ifft to get rippled noise in the time domain
sin_rippledNoise_time = ifft(sin_rippledNoise_freq, 'symmetric');
cos_rippledNoise_time = ifft(cos_rippledNoise_freq, 'symmetric');
% Determine the ripple type (ascending vs. descending)
switch rippleType
case 'ascending'
combinedRippledNoise_time = sin_rippledNoise_time + cos_rippledNoise_time;
case 'descending'
combinedRippledNoise_time = sin_rippledNoise_time - cos_rippledNoise_time;
end
% Calculate the final rippled stimulus in the time domain
rippledStimulus_time = pinkNoise_time + modulationDepth * combinedRippledNoise_time;
N.B. when the density is zero 'rippled_noise' by itself has an envelope of a rectified sine wave (which has double the velocity). Only after adding the original noise the envelope is the correct one.
Band filter method
%todo
References
% todo