Sharif University of Technology Department of Computer Engineering CE242, Signals and Systems, Fall 2007 Prof. H. R. Rabiee Lab#1 The objectives of this assignment are: • To experiment with sound signals • To experiment with noisy signals This assignment consists of two part. In the first part, you will become familiar with reading and a sound signal from the real world, manipulate it and convert it to an audio signal; and in the last part, you will manipulate signal with some kind of noise and then you should recover the signal from the noise. Part 1: Sound Signals • Choose a piece of an audio signal ‐ which you must take from me ‐ with large enough samples (typically more than 200000). • Plot the magnitude of its FT. Note that frequency axis should be indexed with appropriate values with respect to sampling frequency. • Plot the phase of its FT. • Determine the range of frequency for which the content of signal is significant. • Eliminate the portion of the signal spectrum which is corresponding to the frequencies above 8 KHz. • convert the signal to audio and listen to it. Explain the difference. Part 2: Noise • Add a uniform noise to the original signal. • Plot the magnitude of FT of noisy signal and compare with original signal. • Regarding result of previous part, explain the effect of noise. • Convert the noisy signal to audio signal and listen to it. Hints: • [y,Fs,bits] = wavread('filename',[N1 N2]) Read Microsoft WAVE (.wav) sound file specified in the ‘filename’ and load its data to vector y (samples N1 through N2). Fs returns the sampling frequency and bits returns the number of bits used for encoding. • wavwrite(y,Fs,N,'filename') Writes the data stored in the variable y to a WAVE file called ‘filename’. Fs is sample rate and N is the number of bits used for encoding. N = 8, 16, 24, or 32 • How to make a signal noisy? Y = rand (m,n) generates uniformly distributed random numbers (noises) over [0,1] interval. In order to generate a uniform distribution of random numbers on a specified interval [a,b], multiply the output of rand by (b‐a), then add a. • Use the following command to the first part of assignment: fft, abs, angle Note: You should send me a .pdf document which contains all the figures asked in the assignment + necessary explanation of each part. Your audio signals must be in a separate folder “Audio” with having referenced in the main document. Assignments without Matlab codes will not be graded. Upon having any problem, contact [email protected]. Good Luck Reyhaneh Jabarvand