EECE301 Discussion 12a DT Filter Applications

EECE301 Discussion 12a DT Filter Applications - EECE 301...

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EECE 301 Prof. Mark Fowler Discussion #12a • DT Filter Application
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These notes explore the use of DT filters to remove an interference (in this case a single tone) from an audio signal. Imagine that you are in the your home recording studio and have just recorded what you feel is a “perfect take” of a guitar solo for a song you are recording, but you discover that someone had turned on some nearby electronic device that caused electromagnetic radiation that was picked up somewhere in the audio electronics and was recorded on top of the guitar solo. Rather than try to recreate this “perfect take” you decide that maybe you can design a DT filter to remove it. We will explore two different cases: i. a high-pitched tone that lies above the significant portion of the guitar signal’s spectrum, and ii. a mid-pitched tone that lies in the middle of the guitar signal’s spectrum.
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Amp & AA Filter ADC Store in Memory Interference DT Filter (Implemented in S/W & run by CPU) Store in Memory DAC Amp Real Set-Up
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I. Signal Access and Exploration 1. Use MATLAB’s wavread command to load the guitar1.wav file 2. Listen to the guitar signal using MATLAB’s sound command. 3. Plot the first second or so of the signal in the time domain to see what the signal looks like. 4. Look at the guitar signal in the frequency domain by computing and plotting (in dB) the DFT of various 16384-pt blocks of the guitar signal. Verify that the significant portion of the guitar signal’s spectrum lies below 5 kHz.
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%%%%%% I. Signal Access and Exploration %%%%%%%%%% [x,Fs]=wavread('guitar1.wav'); x=x.'; % convert into row vector sound(x,Fs); t=(0:49999)*(1/Fs); plot(t,x(1:50000)) X1=fftshift(fft(x(20000+(1:16384)),65536)); X2=fftshift(fft(x(40000+(1:16384)),65536)); X3=fftshift(fft(x(60000+(1:16384)),65536)); X4=fftshift(fft(x(80000+(1:16384)),65536)); f=(-32768:32767)*Fs/65536; Figure; subplot(2,2,1); plot(f/1e3,20*log10(abs(X1))); subplot(2,2,2); plot(f/1e3,20*log10(abs(X2))); subplot(2,2,3); plot(f/1e3,20*log10(abs(X3))); subplot(2,2,4); plot(f/1e3,20*log10(abs(X4)));
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II. Adding A High Frequency Interference 1. Create a sinusoid whose frequency is 10kHz that is sampled at the same rate as the guitar signal and has the same length. The amplitude of this sinusoid should be 1.
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This note was uploaded on 02/29/2012 for the course EECE 301 taught by Professor Fowler during the Fall '08 term at Binghamton University.

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EECE301 Discussion 12a DT Filter Applications - EECE 301...

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