You can download the shareware program GoldWave from www.goldwave.com. It comes up with two windows, as shown below.

When you click new, you get the window shown below. Just accept the settings shown there, possibly changing the time to something shorter, like 10 seconds.

You get a subwindow in which your sound will be pictured. Now go to the menu and select Tools-Expression evaluator.

In the window that opens up, enter the expression you want to hear. In the picture below, it's sin(440*2*pi*t), which is a wave with frequency 440. This should give us a musical note A. Click start to have your expression evaluated. This may take some time.

The sound looks like a solid green glob, but when you play it, you get a better picture of what's happening. To play it, go to the device control window and click one of the green arrows.

To modify the expression, select the expession evaluator tool again. Modify the expression as you wish, and click start again. Here is what I saw after I changed the expression to sin(440*2*pi*t)+1/3*sin(3*440*2*pi*t). So we do get a good graphical picture of the sound as well as being able to hear it.