KG: If you can hook up a cable from the line level out of your computer, you can download a program off the net. While this might not be exactly what you were looking for, it might give you what you want with little to no further expenditure. Even if you don't need it now, it may come in handy later.
Head over to Marchand and download their FG Lite.exe
program on this page. The FG stands for Function Generator and it allows you to generate a sine, square or triangle waveform at any given frequency that you want. Simply program in a frequency, select the type of waveform and have at it. You can even do pre-programmed sweeps starting at XX Hz and stopping at XXX Hz if you like. If you want to get "crazy", you can generate very complex waveforms by having multiple signals going. This is done by opening up several different FG's at one time and programming them individually. Real cool stuff, all for free from Marchand.
If you want to go another route, i would highly suggest purchasing a very versatile tool that will pay for itself in the long run. That is, take a gander at a decent multimeter with a frequency counter built into it. The Tenma 72-4025
will will do just about anything that you'll ever need or want for "tinkering" and won't break the bank. It is a multi function Digital Multi-Meter
of more than reasonable accuracy for what you want. It can measure voltage, resistance, current, capacitance, frequency, transistor's, digital logic, diode's, continuity, etc... AND it does it all for $39.99!!! Talk about the "trickle down" effect of technology!!! The first DMM that i bought that could do all of this was over $600 MSRP!!! For the record, i was able to find it for $130 brand new. I'm good like that : )
I hope this helps. I'm always glad to see someone striving towards a better understanding of audio and being able to fix their own problems. A better understanding of what you are dealing with not only helps you solve such problems, it will also help you to "de-bunk" a lot of what you are told by so-called "experts" on the subject. Believe me, once you start getting your hands dirty and understanding what is going on in your room and equipment, you'll never read another review with the same frame of mind ever again. Sean