 # Filtering Garbled Voice Recording

Subject Engineering MATLAB for Engineering

## Question

You are supplied a recording of a person saying a specific data and time in a .wav file.
Unfortunately while recording, a fire truck passes by and masks the speech with a loud siren sound. Your task is to low pass filter the given signal such that the speech signal is cleat enough to hear the spoken day and time.

Requirements
First decide on the low pass filter requirements such as pass band and stop bend frequencies based on the spectrum of a typical male voice. Describe how these values were chosen. The filter order should be the lowest value needed that result in a clear date and time.
After filtering you will notice some ‘in-band’ interference from aliasing of the siren. To mitigate this interference some editing based on signal amplitude may be needed.

Implement the low pass filter using the three IIR filter: Butterworth, Chebyshev I and Elliptical using Matlab. Provide magnitude plots of the filter’s frequency response in dB vs. radian frequency (0 to pi), phase plots using Matlab unwrap and angle commands, and the group delay.
You are then to implement the low pass filter using the Kaiser Window Method as outlined in section 7.5.3. Do not use the fdatool for this part of the project. Provide a magnitude plot of the filter’s frequency response in dB vs. radian frequency (0 to pi). Also provide a pole-zero plot for this filter.

Textbook: Alan V. Oppenheim and R.Schafer, Discret-Time Signal Processing, 3rd edition. ISBN: 0-13-198842-5

## Solution Preview

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function Hd = Butterworth
%BUTTERWORTH Returns a discrete-time filter object.

% MATLAB Code
% Generated by MATLAB(R) 8.3 and the Signal Processing Toolbox 6.21.
% Generated on: 02-May-2015 14:01:49

% Butterworth Lowpass filter designed using FDESIGN.LOWPASS.

% All frequency values are in Hz.
Fs = 16000; % Sampling Frequency

Fpass = 2000;       % Passband Frequency
Fstop = 2500;       % Stopband Frequency...

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