How to generate a sine signal with changing frequency, but with predetermined number of elements and periods?

Hi.

I have to generate (plot) a sine signal which should have predetermined number of elements (lat say 200000) and predetermined number of periods (20). That means, 10000 elements per period.

The function (or a script) should also provide an option to freely select how the frequency is changing between those 20 periods. Actually, I want to change frequency anywhere between 1 Hz and 50 Hz. Let say, from 1 Hz to 50 Hz and then back to 1 Hz. Or, from 1 to 5 Hz in first 15 periods and then accelerate to 50 Hz in last 5 period. Possibilities are endless, but first two conditions (num. of elements and periods) should always be met.

I have made a script, but this is not exactly what I want. The code is attached below. Problem here is, that the number of periods is not OK. Here I am changing a frequency with values in array "Freq". If Freq = [1 20 1], then frequency will change from 1 to 20 (in the middle) and back to 1 Hz. This way I can change a frequency as I want, but the number of periods is not constant (20).

I would be very grateful, if someone could help me with that problem.

Thank you in advance.

 clear all;

 Freq = [1 20 1];

 % Number of elements
 Fs = 200000;

 Ts = 1/Fs;
 T = 0:Ts:1-Ts;
 N = Fs / (length(Freq)-1);

 switch numel(Freq)
   case 1
     FreqArray(1,1:Fs) = Freq(1);
   case 2
     FreqArray = linspace(Freq(1), Freq(2), N);
   case 3
     FreqArray = [linspace(Freq(1), Freq(2), N) linspace(Freq(2), Freq(3), N)];
   case 4
     FreqArray = [linspace(Freq(1), Freq(2), N) linspace(Freq(2), Freq(3), N)...
                 linspace(Freq(3), Freq(4), N+2)];
   case 5
     FreqArray = [linspace(Freq(1), Freq(2), N) linspace(Freq(2), Freq(3), N)...
                 linspace(Freq(3), Freq(4), N) linspace(Freq(4), Freq(5), N)];
   case 6
     FreqArray = [linspace(Freq(1), Freq(2), N) linspace(Freq(2), Freq(3), N)...
                 linspace(Freq(3), Freq(4), N) linspace(Freq(4), Freq(5), N)...
                 linspace(Freq(5), Freq(6), N)];
   case 7
     FreqArray = [linspace(Freq(1), Freq(2), N) linspace(Freq(2), Freq(3), N)...
                 linspace(Freq(3), Freq(4), N) linspace(Freq(4), Freq(5), N)...
                 linspace(Freq(5), Freq(6), N) linspace(Freq(6), Freq(7), N+2)];            
 end

 Phi = 2 * pi * cumsum(FreqArray) / length(T);
 Sin = sin(Phi);

 plot(T, Sin); grid;

Answer 1

[Shane]

Try this: http://www.mathworks.com/matlabcentral/fileexchange/41088-variable-frequency-sine-wave

[matico]

Thanks for sharing this.

In my case, the frequency should not change instantly, but it should change over some range. If I would have defined 2 frequencies (start at 1 Hz and finish at 50 Hz) it should "accelerate" through a whole range of 20 periods. If I have 3 frequencies [1 50 1], it should accelerate from start to the half and then slow down back to 1 Hz.

[rasam aliazizi]

Did you get any luck on this? If so would you mind sharing your findings?

Answer 2

[matico]

Nobody else has any idea? I was trying to modify function, which was suggested by Shane, but with no success.