What are you talking about? There is no single frequency.
Read this and try to understand what do you really want:
http://en.wikipedia.org/wiki/Spectrogram[
^],
http://en.wikipedia.org/wiki/Fourier_transform[
^],
http://en.wikipedia.org/wiki/Fast_Fourier_transform[
^].
[EDIT]
Follow-up discussion:
"Pitch watch system that can change the Frequency of a signal to a note symbol."
It does not "change". This is a very complex problem of the
musical pitch recognition. It's not a "note symbol". This question along shows how far you are. This is a task of recognition of the audio into, technically speaking, a MIDI sequence.
It looks like you have no idea how complex are the issues you're trying to thinks of. If you think that even relatively simple Fast Fourier transform is something difficult to translate in code, I cannot imaging that you can approach the problem of pitch recognition.
I can tell you one thing. I found some free programs for musical pitch recognition, and I worked with human voice recognition readily available on Windows. Even though human voice recognition seems much more complex, I found Microsoft engine quite successful; it works even with my accent in English pretty well and does not require teaching.
In contrast, all I tried for musical pitch recognition was only more or less close, but effectively failing. Even a relatively clear voice of electronic keyboard was barely recognized. The notation scores looked like a mess I would not easily play back, with multiple mistakes. I can understand it. There are no pure tones in any real-life record; music is a wealth of noises and over-tones but not in the frequency-phase space but in time. There is no clear definition of what a pitch is. You should not be mistaken by a easy of recognition by a trained human ear. Maybe the problem is that this task is not in high demand compared to speech recognition. Maybe these days you can find something much better (see below). Maybe, but…
To have an idea on what involved, look here:
http://www.eetimes.com/design/embedded/4006427/A-DSP-algorithm-for-frequency-analysis[
^].
This is an available framework in Java:
http://marf.sourceforge.net/api-dev/[
^].
Don't even try to discuss that this is a different computer language. The problem itself is many orders in magnitude more complex than the barrier between computer languages.
These are the C# articles on very basic techniques of working with audio input and spectral analysis:
Sound visualizer in C#[
^],
Sound Activated Recorder with Spectrogram in C#[
^].
Do this go get into it some more:
http://en.lmgtfy.com/?q=(audio+OR+music)+pitch+recognition+%22C%23%22[
^],
or better
http://en.lmgtfy.com/?q=(audio+OR+music)+pitch+recognition[
^].
I wish you luck. You would need a lot of luck just come close to the problem.
—SA
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