Demodulated_version_of_343058__kb7clx_2tri_DTBLKFX_RemoveHarm.wav

This sound is a transformation of
http://freesound.org/people/kb7clx/sounds/343058/
Please see description of the original sound for full details.

When inspecting the original file's waveform in Audacity, I realized that the carrier tone has a complex wave - The ideal waveform was probably a series of alternating positive and negative pulses, but the actual waveform deviates a lot the shape of rectangular pulses. Most likely due to loss of high frequency contents and maybe phase issues due to cheap sound electronics. Lets remember that the purpose of this unit is to produce an easily audible tone of varying pitch according to light intensity. It is not supposed to produce an exact wave shape or to have hi-fi circuitry.

In any case, what this meant was that the carrier waveform was too complicated for me to remove via demodulation with standard waveforms. I am sure there is a way of typing some copde in the Nyquist prompt in Audacity that could allow a sample portion of the carrier wave to be used to demodulate the whole file. But doing this is beyond my limited ability.

So, I decided to stick to the 101Hz triangle wave as my best approximation for the carrier and to remove the leftover harmonics using the DtBlkFx plugin in Audacity.
The 101Hz fundamental had already been removed by the demodulation process. So with DtBlkFx I removed the partials at ~200Hz, ~400Hz, etc.

This was the result.