# -Filter Design project- DSP (((Help)))

Discussion in 'Homework Help' started by DSP student, Dec 28, 2009.

1. ### DSP student Thread Starter New Member

Dec 28, 2009
1
0
hello everyone,
i need your help in this designing project...

*project preview:
An intelligence agency has intercepted a voice message from a foreign terrorist. Unfortunately, the message has some form of distortion that makes it unintelligible. The voice message was sent to your lab
for analysis

*the Details:

a) Load the wave file associated with your number in the ee360 class. For example, if your number
is 34, load the file named f34.wav using wavread and store it in a variable named x

b) What is the sampling rate Fs of the file you loaded (in Hz)? What is its total length (in sec)?

c) Listen to the sound contained in x. Can you understand the message? What form of distortion
prevents you from understanding the voice message?

d) Plot the first 100 samples of x[n].

e) Compute Xf the FFT of x using Nfft=16000 points. Define a new variable Xfm and let it be
equal to the magnitude of the first 8000 points of Xf. Plot Xfm and make sure that the x-axis
scale is such that it starts at 0 Hz and ends at Fs/2 Hz.

f) Again, plot the magnitude spectrum of x from 0 to 4kHz by using freqz(x,1,F,Fs) and
compare with (e).

g) Plot the spectrogram of x using spectrogram(y2,512,250,512,Fs)and comment on it
to indicate where is the signal and where is the interference.

h) Using the plots (e,f,g), can you identify the cause of the problem? What is it? At which
frequencies is it? What type of filter/filters is needed to remove it, LPF, HPF, or Single Notch?

i) Use fdatool to design an appropriate filter to remove the distortion. Keep the units at Hz

j) Specify all the parameters that you have chosen to design the filter (e.g., fs, fc, fnotch,
Bandwidth,  etc). Note that every type of filter has different parameters, so you must specify
the type of filter that you chose and all its parameters.

k) Click the Design Filter Button. From the File menu click generate m file and choose a
name such as Filter1.m. Repeat if you have more than one filter.

l) The filter parameters can be easily loaded into your program by writing: h1=Filter1

m) What are the coefficients of this filter? What is the filters structure? (Direct form I , II , . etc ?)

n) Plot the frequency response of the filter/filters using: freqz(h1)

o) Use h1 to filter x using: y= filter(h1,x). If you have more than one filter then you need
to filter the output again using the other filters.

p) Plot the spectrogram of the final clean output and comment on it to indicate where is the signal
and where is the interference.

q) Listen to y. Can you understand the voice message now? What is the message?