Signály

Budeme sa zaoberať nasledovnými typmi signálov:

• umelé,
• prírodné,
• audio,
• video.

Umelé testovacie signály

Na testovanie sa používajú umelé signály

• impulz
• skok
• harmonický signál
• šum

• 

  Impulz

• 

  Skok

• 

  Sínus

• 

  Šum

% Uvedene signaly v Octave vyrobime takto

 PulseSignal = zeros(1000,1); PulseSignal(5)=1;
 StepSignal  = zeros(1000,1); StepSignal(6:50)=1;
 SinusSignal = sin(linspace(0,4*pi,100));
 NoiseSignal = 0 + 0.6 * randn([100 1]); % \mu = 0, \sigma = 0.6
 HeartSignal;

% A vsetky naraz nakreslime. Po skonceni skriptu mame signaly
% nachystane v pamati. Mozeme ich dalej pouzivat.
%
 clg; figure(1);
 
 subplot(5,1,1);
 stem(PulseSignal); axis ([0 100 -0.5 1.5]);

 subplot(5,1,2);
 stem(StepSignal,"b"); axis ([0 100 -0.5 1.5]);

 subplot(5,1,3);
 plot(SinusSignal,"g"); axis([0 100 -1.5 1.5]);

 subplot(5,1,4);
 plot(NoiseSignal,"r"); axis([0 100 -1.5 1.5]); 

 subplot(5,1,5);
 plot(heart(:,1),heart(:,2)); axis([0 5 -1 2]);

Download

• signaly.m  

Toto nefunguje (a asi ani nebude): http://virtuallab.kar.elf.stuba.sk/robowiki/images/5/52/Mfile_icon.png signaly.m

Po stiahnutí si súbor uložte ako signaly.m a v Octave napíšte demo signaly.

Harmonické signály

• Počúvanie fázového posunu

V nasledujúcom príklade vytvoríme v Matlabe/Octave harmonický signál a jeho rôzne kombinácie.

• 

  Komorné A (A4)

• 

  Akord (A+Cis+E)

• 

  Zašumené A4

%  Priklad na vytvaranie harmonickych signalov
%  
%  Okrem vykreslovania mozeme spravit export do .wav suboru a potom
%  si vysledne zvuky prehravat a prezerat napriklad v Audacity
%  
%  (c) Richard Balogh, 30. 5. 2008
% 
%
%
% %%%%%%%%%%%%% Signal 1 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

f_sample = 8000;  % [Hz] - pre telefony OK
duration =    1;  % [s]  - jedna sekunda

  time = 0 : (1/f_sample) : duration;
% time = linspace(0,duration,f_sample);  % Alternativa zapisu

freq = 440;                          % Komorne A4 = 440 Hz
   A = 0.9;                          % Amplituda je z intervalu <-1,1>
  fi = 0;                            % Fazovy posun
   
A4 = A * sin(2*pi*freq*time + fi);
	
% plot(A4);                          % Mozeme si aj nakreslit

wavwrite(A4',"sinusA4_8k.wav");      % A4' - wavwrite potrebuje stlpec

% %%%%%%%%%%%%% Signal 2 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

A = 1.9;                             % To iste, ale zvacsime apmplitudu
A4 = A * sin(2*pi*freq*time);
wavwrite(A4',"sinusA4_8k_orez.wav"); % Orezany signal, ma vyssie harmonicke

% %%%%%%%%%%%%% Signal 3 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

f_sample = 44100;                       % [Hz] - CD audio
duration =     1;                       % [s]  - jedna sekunda
    time = 0 : (1/f_sample) : duration;

freq = 440;                             % Komorne A4 = 440 Hz
   A = 0.9;                             % Vratime zasa naspat
   
A4 = A * sin(2*pi*freq*time);
wavwrite(A4',f_sample,16,"sinusA4_44k.wav"); % Musime zadat, ak f_sample != 8k
 
% %%%%%%%%%%%%% Signal 4 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Akord  A4 + C5# + E5
% A4  = 440 Hz
% C5# = 554,37
% E5  = 659,26
% http://www.phy.mtu.edu/~suits/notefreqs.html
%
A4   = A * sin(2*pi*440.00*time);
Cis5 = A * sin(2*pi*554.37*time);
E5   = A * sin(2*pi*659.26*time);
Tone = (A4 + Cis5 + E5)/3;              % Aby amplituda bola <-1,1>
wavwrite(Tone',f_sample,16,"chordA4_44k.wav"); 


% %%%%%%%%%%%%% Signal 5 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Pridame k tonu sumovu zlozku
%
noise    = 0 + 0.2 * randn(size(time)); % \mu = 0, \sigma = 0.2
Tone = (A4 + noise)/2;                  % Aby amplituda bola <-1,1>
wavwrite(Tone',f_sample,16,"noiseA4_44k.wav");

Download

• signalyA4.m

Prírodné signály

Týmto neohrabaným názvom označujem signály, ktoré pochádzajú z reálneho sveta, nie z počítačovej simulácie. Môžete si ich stiahnuť a robiť s nimi neskôr pokusy. Časom snáď pribudnú ďalšie a lepšie.

• 

  Srdce - EKG

• 

  Teplota vzduchu

• 

  Flauta - A4