Revision as of 15:55, 6 September 2011

Sampling of an A 440

Explain how one can use MATLAB to play an A 440. Discuss your choice of sampling rate. (Feel free to post a sound file of your output.)

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Answer 1

The signal we want is $ x(t) = cos(440 * 2\pi) $.

We can first create a vector of sample times. In this case, we'll let the sample frequency be 1320 Hz over a sample interval of [0,1]

t = 0:(1/1320):1;

Next, we can generate the sound samples vector from the sample times vector.

y = cos(440*2*pi*t);

Finally, we play the signal by using the "sound" command, which needs the user to specify the sound vector and the sample rate of that vector. Our sample was 1320.

sound(y, 1320);

The sample frequency was chosen so that it was more than twice the note frequency, so that the signal could be completely recovered from this sample.

Instructor's comments: Did you actually try it in MATLAB? Did it work? -pm

Answer 2

I chose the sample rate to be 1/1000.

n = 1:10000;

x = cos(2*pi*400*n/1000);

x = x';

sound(x)

Answer 3

% The following script plays a pure note A-440.

% It provides an adjustable sampling rate.

sampling_rate = 1500;

% Sampling rate should be larger than Nyquist Rate, i.e. 880Hz in this case.

t = 1:(1/sampling_rate):3;

x = cos(2*pi*440*t);

sound(x,sampling_rate);

Answer 4

Back to ECE438 Fall 2011 Prof. Boutin