# Interpolation/Decimation

Started by August 31, 2004
 I had a real digital signal with digital frequency f1=1/5.Changed the sample rate by a factor of 5/8 through a combination of filtering,decimation and interpolation. Then I plotted the power spectrum of the original signal and then the changed signal.The signal seemd to have been attenuated (apart from the effects of interpolation,decimation i had expected) why? Here is my code: amp = 1; %The amplitude numSam = 64; %Number of samples freq = 1; %Frequency Fs = 5; %Sampling frequency Ts =1/Fs; t = (0:Ts:(numSam-1)*Ts); %Getting the cos wave cosine = amp*cos(2*pi*freq*t); %Getting the fourier transform of the signal and calculating %the power spectrum. fourier = fft(cosine); PowerSpectrum = (abs(fourier)).^2; %Converting the power spectrum to dB. PowerSpectrum_DB = 10.*log10(PowerSpectrum); Fd = (0:(numSam-1))/numSam; %Getting the digital frequency Fd1 = (0:(numSam*5/8-1))/(numSam*5/8); resampledSignal = resample(cosine,5,8); resampledSignal_fft = fft(resampledSignal); resampledSignal_Power = (abs(resampledSignal_fft)).^2; resampledSignal_Power_dB = 10.*log10(resampledSignal_Power); figure(1) subplot(2,1,1); stem(Fd(1:(numSam)/2),PowerSpectrum_DB(1:((numSam)/2)),'b') grid on; xlabel('Digital Frequency'); ylabel('Power Spectrum '); title('\bfPower Spectrum Vs Digital Frequency'); subplot(2,1,2) resampledSignal = resample(cosine,5,8); resampledSignal_fft = fft(resampledSignal); resampledSignal_Power = (abs(resampledSignal_fft)).^2; resampledSignal_Power_dB = 10.*log10(resampledSignal_Power); stem(Fd1(1:(numSam)/2),resampledSignal_Power_dB(1:((numSam)/2)),'r') grid on;