building stuff, more stuff, and a little bit of… stuff
UPDATE: Maybe I wasn’t so far off after all. Neurophone inventor Patrick Flanagan has since confirmed the TL494 pseudo-Neurophone design CAN produce Neurophone effects, though it’s still probably not as good as the real thing. Some research suggests this is why: TL494’s square-wave output gets differentiated by the piezos (which are capacitors), producing a “Lilly wave”-like signal that mimics signals produced by nerves. (The Lilly Wave, as far as I understand, is a sharp positive spike followed by an equal but negative one. The idea is the first peak transports something, I think ions, across the barrier between nerves while negative spike brings them back so the nerves can use them again.)
The TL494 pseudo-“Neurophone” is pretty far off from a real one. Here’s why.
It turns out Flanagan’s Neurophone does two things:
- It replaces the rising and falling edges of the audio signal wave with edges that have the _slope_ of a 40-50kHz ultrasonic wave. The 40kHz carrier is unimportant, the slope is key.
- It then double differentiates and highpass filters the result. This mimicks what would happen if you fed the signal into an antenna and then received the electromagnetic waves with your brain! The double-differentiated signal is now converted to mechanical energy with a piezo speaker, bypassing the brain’s radio receiver.
The implication of this is that there are bits of our brain that act as a radio receiver with 100kHz bandwidth, and can process incoming audio. Which is crazy.