[sdiy] Hiss, Crackle, and Pop

[Tom Wiltshire]

Hi all,

Here's what I've been working on the last couple of days. I call it "Hiss, Crackle, and Pop" since that's what it does. It's a dose of instant added "vintage" character for whatever you add it to. ;)

	http://electricdruid.net/wp-content/uploads/2017/04/HissCracklePop.jpg

The basic gist of it is that the PIC uses a long (47-bit) LFSR to generate noise on three channels. The code also produces two channels of random trigger pulses, one frequently (the "Crackle" channel) and the other more infrequently (the "Pop" channel). These trigger pulses are shaped into a basic decay envelope and used to control the volume of the noise channels. These are tone-shaped to give them different characters, and then the whole mess is mixed back together.

Here's what it sounds like. First, the three elements separately, then the mix.

	http://electricdruid.net/sounds/HissCracklePop.mp3

If anyone spots anything stupid/odd in the schematic, I'd appreciate any pointers. Particularly the mixer, since I borrowed the design and then modified it to run at 5V. Designing with transistors is not something I've really done much, and I was mostly making it up as I went along. Here's the original mixer:

http://www.electroschematics.com/2917/audio-mixer-with-one-transistor/

The VCA's are the Roland "Swing type" VCA, from the DR110 and probably elsewhere, so I'm pretty happy about that part.

Enjoy!
Tom