MATLAB: Need help with this

audio filterfft

turn all the amplitudes of frequencies which are higher than 3500 Hz into 0’s and amplify the rest of the spectrum (by just multiplying the spectrum by some large number so that the amplitudes are around 2000-3000 in magnitude

how do i do this ? like what would the code be like?

Best Answer


a = [10;15;3600;4500;45;67;100];
[ind,~] = find(a>=3500);
b = a;
b(ind) = 0;
c = b*30

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MATLAB: Efficient pass filters for EEG signals

The lowpass function (and those like it) have 2 outputs, the second being a digital filter object. Save the digital filter object and use it with filtfilt to use it with other signals.

That is much more efficient than designing it each time you use it, which is what it appears you are doing now. So, design it once and use it as often as necessary afterwards.

MATLAB: I need to get the maximum amplitude in this code but the final answer is wrong

‘i am fairly certain my code is wrong’

So am I.

Try this:

D = load('Data.mat');
f = D.f;
t = D.t;
dt=t(2)-t(1);% t vector has equally spaced t so this seprates t values
N=numel(t);
F=fft(f)/N; %fast fourier transform of f/N
Fshifted=fftshift(F);%place 0 frequency in the centre
Fmag=abs(Fshifted);%magnitude of fshifted 
nu_NY=(1/dt)/2;%nquist frequency 
nu=linspace(-nu_NY,nu_NY,N);%spectrum of frequncy vals associated with FFT frequencies 
%adding postive and negative frequncies 
F1=Fmag((N/2)+1:N);
F2=Fmag(N/2:-1:1);
% a=[F1,0]+[0,F2];
%plotting amplitued vs assoicated frequencies
plot(nu,abs(Fshifted)*2)
[pks,locs] = findpeaks(abs(Fshifted)*2, 'MinPeakHeight',10);
fprintf(1,'Peak Frequencies & Amplitudes:\n\tFrequency\tAmplitude\n')
fprintf(1,'\t%8.4f\t%8.4f\n', [nu(locs); pks])

producing:

Peak Frequencies & Amplitudes:
	Frequency	Amplitude
	 -7.9790	 14.2000
	  8.0290	 14.2000

My changes are primarily with respect to ‘nu’, although I also correctly scaled the result of your fft call. I added a call to findpeaks (link). (I did not delete parts of your code that I believe to be irrelevant to what you want to do.)

Best Answer

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MATLAB: Efficient pass filters for EEG signals

MATLAB: I need to get the maximum amplitude in this code but the final answer is wrong

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