why should we multiply the number of samples with sound frequency to calculate the sine wave?

I have a code that aims to produce sine waves for durations of interest. in line related to creating sine wave, it's written:

tone_dur = sin(2*pi*freqs*t);

t is the number of samples needed for each tone duration and freq is the tone frequence (500 Hz). What I don't get is that why should we multiply the number of samples with sound frequency to calculate the sine wave? I don't get the rational!

Answer 1

[Geoff Hayes]

joly - I think that t is usually a time array (in seconds). From fft examples, t can be initialized as

Fs = 1000;            % Sampling frequency                    
T = 1/Fs;             % Sampling period       
L = 1500;             % Length of signal
t = (0:L-1)*T;        % Time vector

Then you should be able to continue as before.

If t were just the number of samples, i.e. a scalar, then tone_dur would be a scalar value as well....and I don't think that is exactly what you want.

[joly Alipor]

Actually t is not a scalar. :

sampleFreq = 44100;

dt = 1/sampleFreq;

t = [0:dt:intervals(i)];

Now can we still say that t is a time array (in seconds)?

[Geoff Hayes]

joly - you had posted (before including any code) that t is the number of samples which (to me) describes a scalar and not an array.

In the above code, the units for sampleFreq is samples/second, so dt will be seconds per sample. What are the values for intervals since you haven't posted that? What does t mean to you then?

[joly Alipor]

Now to me t is an (1*n) array describing the time. Is it right?

interval(i), say interval(1) is 0.230 s.

[Geoff Hayes]

If interval is a time i.e. 0.230 seconds, then t, which is an array from 0 to interval(k), would be an array describing time.

[joly Alipor]

That's exactly right. Thanks a lot for your great help.