How could i give audio file as an external input to system in matlab ?

Hello,

I have matlab code. Right now in this code i am giving fi as a external input that is fi = cos(10*Tspan) but instead of this how could i give audio file or *.wav file as an external input to this system ? I have read wavread function but not getting idea.

As per my perception, if i have for example engine.wav file then should i right fi = wavread(engine.wav) and this fi i can used as a external input ? or i have to write something extra for this ?

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function dz = myeqd(t,y,ti,fi)

dz = zeros(3,1);

mu=0.7;

r= sqrt(y(1)^2 + y(2)^2);

K=2;

F=interp1(ti,fi,t);

dz(1)= (mu - r^2)*y(1) - y(3)*y(2) +K*F;

dz(2) = (mu - r^2)*y(2) + y(3)*y(1);

dz(3) = (-K*F) * (y(2)/sqrt(y(1)^2 + y(2)^2));

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then call this function

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Tspan= 0:0.01:500; % time vector

fi = cos(10*Tspan); % external perturbation

ti=Tspan;

[T,Y]=ode45(@(t,y) myeqd(t,y,ti,fi),Tspan,[1;1;30]);

plot (T,Y(:,3))

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thank you

Answer 1

[Walter Roberson]

Yes, you can use fi = wavread('engine.wav');

Do be careful, though: many audio files are stereo, and so wavread() would result in two columns but your code appears to be expecting only one column.

Answer 2

[Aniket]

thanks Walter

and small doubt if the file is stereo then i have to use left and right coloumn and if file is mono then i can directly use fi as an input ?

[Walter Roberson]

Yes.

Answer 3

[Jan]

Exactly:

fi = wavread('engine.wav')

Be sure to catch the frequency also, otherwise you cannot correlate the signal with the real time.

But a problem remains: You function to be integrated has discontinuities caused by the linear interpolation of a discontinuos perturbation. The stepsize control of ODE45 requires a smooth function, see: http://www.mathworks.com/matlabcentral/answers/59582#answer_72047. In consequence you can get 1. long runtimes and inaccurate results, 2. a warning and inaccurate results, or 3. an error, which stops the integration depending on the input data. From a scientific point of view, this is not a reliable calculation and therefore a waste of time.

[Aniket]

hello Jan

How could i catch the frequency of sound file ?

[Jan]

@Aniket: The documentation of wavread reveals the relevant details: doc wavread . While this should be easy, handling the discontinuities remains a serious problem.

[Aniket]

Hello Jan

as per your comment i am facing same problem , its giving me inaccurate results . Then how should i solve this discontinuities? should i use simulink model for above equation instead of ode45 ? please give me suggestions and guidance.

Thanks in advance

[Jan]

Try a fixed step solver and define the steps such, that they happen at the discontinuous changes of the right hand side.

[Aniket]

Means you are saying i have to use simulink ? because simulink using fixed step solver ...i have searched in matlab doc about fixed step but i am not getting any search result .

[Walter Roberson]

http://www.mathworks.com/matlabcentral/newsreader/view_thread/272631