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Lecture Series on Digital Signal Processing by Prof.T.K.Basu, Department of Electrical Engineering, IIT Kharagpur. For more details on NPTEL visit http://nptel.iitm.ac.in
Views: 40936 nptelhrd

13:12
http://AllSignalProcessing.com for more great signal processing content, including concept/screenshot files, quizzes, MATLAB and data files. FIR filters with generalized linear phase can have even or odd order and even or odd symmetry, resulting in four different types. Constraints on the frequency response and zero locations are presented for each filter type.
Views: 37994 Barry Van Veen

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00:38 Fs=8000; %Specify Sampling Frequency Ts=1/Fs; %Sampling period. Ns=512; %Nr of time samples to be plotted. t=[0:Ts:Ts*(Ns-1)]; %Make time array that contains Ns elements %t = [0, Ts, 2Ts, 3Ts,..., (Ns-1)Ts] f1=500; f2=1500; f3=2000; f4=3000; x1=sin(2*pi*f1*t); %create sampled sinusoids at different frequencies x2=sin(2*pi*f2*t); x3=sin(2*pi*f3*t); x4=sin(2*pi*f4*t); x=x1+x2+x3+x4; %Calculate samples for a 4-tone input signal %N=16; %FIR1 requires filter order (N) to be EVEN %when gain = 1 at Fs/2. %W=[0.4 0.6]; %Specify Bandstop filter with stop band between %0.4*(Fs/2) and 0.6*(Fs/2) %B=FIR1(N,W,'DC-1'); %Design FIR Filter disp('Please specify the filter type'); FilterType={'low','high','bandpass','stop'}; disp('Here is the filter option:'); disp('1: Low Pass Filter '); disp('2: High Pass Filter'); disp('3: Band Pass Filter'); disp('4: Band Stop Filter'); disp('You only need enter number. EX. 4 means Band Stop filter') FilterOption=input('FilterOption='); while FilterOption ~=1 && FilterOption ~=2 && FilterOption ~=3 && FilterOption ~=4 disp('You only need enter number : 1,2,3 or 4. EX. 4 means Band Stop filter'); FilterOption=input('FilterOption='); end userFilterType=FilterType{FilterOption}; disp('Enter the order of the filter(Must be a positive even number, should be less than 100'); FilterOrder=input('FilterOrder='); str=sprintf('Here is all the frequency infromation in this experiment:Fs=%d; f1=%d; f2=%d; f3=%d; f4=%d;',Fs,f1,f2,f3,f4); disp(str); if FilterOption==1 disp('Enter the Edge Freq. in Hz. Note: the value should be within 0~Fs');W=input('omega='); elseif FilterOption==2 disp('Enter the Edge Freq. in Hz. Note: the value should be within 0~Fs');W=input('omega='); elseif FilterOption==3 disp('Enter the Edge Freq. in Hz. Note: the value should be within 0~Fs');W=input('omega cutoff1=');W2=input('omega cutoff2='); W=[W W2]; elseif FilterOption==4 disp('Enter the Edge Freq. in Hz. Note: the value should be within 0~Fs');W=input('omega cutoff1=');W2=input('omega cutoff2='); W=[W W2]; end %Fs, W, W=W./(Fs/2); % [1600 2400] N=FilterOrder; Window_Option={'hamming','rectwin'}; disp('Here is the Windowing option:'); disp('1: hamming'); disp('2: rectwin'); WindowOption=input('WindowOption='); while WindowOption ~=1 && WindowOption ~=2 disp('You only need enter number : 1 or 2 means rectwin'); WindowOption=input('WindowOption='); end %WindowOption='rectwin'; switch Window_Option{WindowOption} case 'hamming' userWindow=hamming(N+1); case 'rectwin' userWindow=rectwin(N+1); otherwise disp('Wrong windowing option. EXIT'); eixt end %B=FIR1(N,W,'bandpass',userWindow); %Design FIR Filter B=fir1(N,W,userFilterType,userWindow); %Design FIR Filter %B %Leaving off semi-colon causes contents of %B (the FIR coefficients) to be displayed. A=1; %FIR filters have no poles, only zeros. figure; zerophase(B,A); disp('Checking the Zero-Phase Response of the designed filter, enter any key to continue'); pause; figure; %Create a new figure window, so previous one isn't lost. freqz(B,A); %Plot frequency response - both amp and phase response. disp('Checking the Freq. Response of the designed filter, enter any key to continue'); pause; figure; subplot(2,1,1); %Two subplots will go on this figure window. Npts=200; plot(t(1:Npts),x(1:Npts)) %Plot first Npts of this 4-tone input signal title('Time Plots of Input and Output'); xlabel('time (s)'); ylabel('Input Sig'); %Now apply this filter to our 4-tone test sequence y = filter(B,A,x); subplot(2,1,2); %Now go to bottom subplot. plot(t(1:Npts),y(1:Npts)); %Plot first Npts of filtered signal. xlabel('time (s)'); ylabel('Filtered Sig'); disp('Checking the Filtering Effect of the designed filter in time domain, enter any key to continue'); pause; figure; %Create a new figure window, so previous one isn't lost. subplot(2,1,1); xfftmag=(abs(fft(x,Ns))); %Compute spectrum of input signal. xfftmagh=xfftmag(1:length(xfftmag)/2); f=[1:1:length(xfftmagh)]*Fs/Ns; %Make freq array that varies from %0 Hz to Fs/2 Hz. plot(f,xfftmagh); %Plot frequency spectrum of input signal title('Input and Output Spectra'); xlabel('freq (Hz)'); ylabel('Input Spectrum'); subplot(2,1,2); yfftmag=(abs(fft(y,Ns))); yfftmagh=yfftmag(1:length(yfftmag)/2); %Plot only the first half of FFT, since second half is mirror image %the first half represents the useful range of frequencies from %0 to Fs/2, the Nyquist sampling limit. plot(f,yfftmagh); xlabel('freq (Hz)'); ylabel('Filtered Signal Spectrum');

54:04
Multistage filter design