%% L12_Audio_Filtering
%% ======================
%% Script to illustrate application of Butterworth filters (lowpass, 
%% highpass, bandpass and bandstop) to a digital audio signal.
%%
%% Created  : 24 Aug 2005
%% Modified : 24 Aug 2005
%%
%% Copyright (c) 2005 Salman Durrani.
%% ------------------------------------------------------------

clc
clear all
close all

%% wav file
[Ysignal,Fs]=wavread('speech_dft');
% [Ysignal,Fs]=wavread('wchimes30');

%% Chip.mat is available inside Matlab
%% Fs=8192 Hz
% load chirp
% Ysignal=y;

%% Nyquist Freq
Fn = Fs/2;
%% Filter order = 2*n
n=8;

%% Low pass filter
Fc=1000;
[num,den] = butter(n,Fc/Fn,'low');

%% High pass filter
% Fc=1000;
% [num,den] = butter(n,Fc/Fn,'high');

%% Bandstop filter
% Fc= [300 1500];
% [num,den] = butter(2,Fc./Fn,'stop');

%% Bandpass filter
% Fc= [3000 3200];
% [num,den] = butter(n,Fc./Fn);

%% Analyse filter
fvtool(num,den)

%% Apply the filter 
Yfiltered = filter(num,den, Ysignal);

%% Compare time domain signal 
figure
subplot(2,1,1)
plot(Ysignal); 
title('Original Signal')
xlabel('Time Sample n')
ylabel('Amplitude')
subplot(2,1,2)
plot(Yfiltered); 
title('Filtered Signal')
xlabel('Time Sample n')
ylabel('Amplitude')

%% Compare spectrum
figure
subplot(2,1,1)
PlotFFT(Ysignal,Fs); 
title('Original Signal')

subplot(2,1,2)
PlotFFT(Yfiltered,Fs); 
title('Filtered Signal')

%% Play sound
wavplay(Ysignal,Fs)
pause(2);
wavplay(Yfiltered,Fs)