Frequency Spectrum

DDG Goodie, as discussed in:
https://dukgo.com/ideas/idea/238/wave-frequency-audible-and-visible
https://dukgo.com/forum/thread/4733/html-5-graphics-audio-in-an-instant-answer-goodie

(my DDG username is 'danielh')

I decided to not start on the oscillator or do other examples of frequencies yet and just implemented an answer with spectrum details about specific frequencies.