% ke spusteni tohoto programu potrebujete funkce readl16 a writel16 
% z http://www.fit.vutbr.cz/~cernocky/speech/matlab

% zprasime recovy signal 1000 Hz a pak ho prefiltrujeme ... 
s = readl16('test.l16',0,inf); s = s/32768; soundsc(s); 
L = length (s); 

% vyrobime 50Hz:
n50 =  sin (2*pi*1000/8000 * (1:L)); soundsc(n50); 

% secteme
y = s + n50;  soundsc(y); 

% jeste to zapiseme do souboru, ktery pak budeme filtrovat pomoci 
% programu v c ...
yout = y / max(abs(y)); writel16 ('y',yout * 32767)

% vyrobime filtr
Wp = [900 1100] / 4000;  % pass-band
Ws = [950 1050] / 4000;  % stop-band
Rp = 3;               % zvlneni pass
Rs = 40;              % potlaceni stop

[N, Wn] = ellipord(Wp, Ws, Rp, Rs)
[B,A] = ellip(N,Rp,Rs,Wn,'stop')

% jakou ma frekv. char ?
freqz (B,A,512,8000); 
%slidify (1,3,1,10) 

% a co poly a nuly ? 
zplane (B,A)

% prefiltrovat a zahrat vystup: 
out = filter (B,A,y); soundsc (out); 

% ukaz koeficienty:
format long
A
B

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
ted uz ne v Matlabu, ale na prikazove radce:

# ve Windous neumim prehravat lin-soubory (GoldWave, CoolEdit ?)
# v Linuxu takhle:

# originalni
play -t .raw -f s -s w -r 8000 test.l16
# zacuneny
play -t .raw -f s -s w -r 8000 y.l16

# filtrujeme
filter y.l16 out.l16

# a zahrajeme si vysledek:
play -t .raw -f s -s w -r 8000 out.l16