Function to create a sound --> (Error: Too many Input Arguments?)

So, I am required to creat a function that displays a simple tone, based on a numerical value corresponding to a key number, a duration, and an amplitude.

After messing around a bit, I came up with this. This does in fact display a sound, but I do not know if it is correct.

     function x = note(keynum, dur, A)
        fs = 44100;                          % sampling frequency
        freq=440*2^((keynum-49)/12);
        t = 0:1/fs:dur; 
        x = A*sin(2*pi*freq*t); 
        plot(t,x); 
        sound(x,fs)

While I think this could be correct, I am confused as to the purpose of an "(sine wave?)" equation we are required to use.

That equation is apparently:

%x(t) = (A)sin(2 pi f t) + (A/3)sin(2 pi(3f)t) + (A/5)sin(2 pi(5 f)t) + (A/7)sin(2 pi(7f)t)

I assume this is some sort of way of creating a more pure and accurate sound, but am not sure.

I tried replacing this equation with the line %x = A*sin(2*pi*freq*t); in my first function( at Line marked with (%%%), resulting in a new function:

function x = note(keynum, dur, A)
  fs = 44100; % sampling frequency
  freq=440*2^((keynum-49)/12); 
  t = 0:1/fs:dur; 

   x(t) = (A*sin(2*pi*(freq)*t)) + ((A/3)*sin(2*pi*(3*freq)*t)) + ((A/5)*sin(2*pi(5*freq)*t)) + ((A/7)*sin(2*pi*(7*freq)*t));     %%%

   plot(t,x); 
   sound(x,fs)

So, I figured I had this all figured out, but when I call the function with, for example a Middle C tone, duration of 1, and an amplitude of 2, %x=note(40,1,2), I get an error:

     ??? Error using ==> pi

     Too many input arguments.

     Error in ==> note at 5          (Line 5 is marked with %%%)

The first function gave a response, but the new one doesn't.

So, I have no idea if I did EVERYTHING wrong in regards to my function and the usage of the (sine wave?) equation is wrong, or its a simple mistake I am not catching.

Any help or pushes in the right direction would be greatly appreciated. I can try to provide more details if needed. Thanks in advance.

Answer 1

[Walter Roberson]

You coded

pi(5*freq)

when you meant

pi*(5*freq)

[Spencer]

Thank you! I would have likely not even noticed that.

Unfortunately I am now getting

??? Subscript indices must either be real positive integers or logicals.

Error in ==> note at 5

However, I think I am on the right track, and will continue to tweak and experiment.

[Spencer]

Never mind, got it,Somehow I left the (t) in when assigning the equation to x.

Thanks again!

[Walter Roberson]

Your t are not integer, but you are trying to store into x(t). You should just be storing to x, not x(t)

Answer 2

[sing lai]

I try to use your code, but there is error in this line: freq=440*2^((keynum-49)/12) why?