감마톤 필터

A gammatone filter is a linear filter described by an impulse response that is the product of a gamma distributionand sinusoidal tone. It is a widely used model of auditory filters in the auditory system.

출처: <https://en.wikipedia.org/wiki/Gammatone_filter>

감마톤 필터 대역폭은 1.01일 때와 필터 차수 4일 때 청각 특성을 가장 잘 반영한다.(한국음향학회 논문). 아래 매트랩 툴박스의 감마톤 필터의 필터 차수는 4로, 대역폭은 1.019로 설정되어있다. (gammatoneFast.m파일 참고)

Matlab Toolbox - need to install

bm = gammatoneFast(x,cfs,fs) 

bm = gammatoneFast(...,align) 

[bm,env] = gammatoneFast(...) 

[bm,env,delay] = gammatoneFast(...)

NOTE: this function is now available from the IoSR Matlab Toolbox as iosr.auditory.gammatoneFast. 

<Example>

fs = 48000; % sample rate 

numchans = 8; % number of frequency channels 

t = -0.005:1/fs:0.025; % time (s)

% impulse 

imp = zeros(numel(t), 1); 

imp(t==0) = 1;

% centre frequencies 

cfs = iosr.auditory.makeErbCFs(500, 7500, numchans);

% calculate impulse response fine structure 

x1 = iosr.auditory.gammatoneFast(imp, cfs, fs); 

x2 = iosr.auditory.gammatoneFast(imp, cfs, fs, true);

% normalise each frequency for plotting 

for c = 1:numchans 

x1(:, c) = x1(:, c) ./ max(abs(x1(:, c))); 

x2(:, c) = x2(:, c) ./ max(abs(x2(:, c))); 

end

% draw 

figure 

% non-phase aligned 

subplot(1, 2, 1), iosr.figures.multiwaveplot(t*1000, 1:numchans, x1') 

h = gca; 

% phase aligned 

subplot(1, 2, 2), iosr.figures.multiwaveplot(t*1000, 1:numchans, x2') 

h(2) = gca; 

% plot settings 

set(h, 'yticklabel', num2str(round(cfs)')) 

for n = 1:2 

xlabel(h(n), 'Time [ms]'); 

ylabel(h(n), 'Frequency [Hz]'); 

end 

title(h(1), 'Non-phase-aligned gammatone filterbank') 

title(h(2), 'Phase-aligned gammatone filterbank')

출처: <https://kr.mathworks.com/matlabcentral/fileexchange/32212-gammatone-filterbank>