[sdiy] Hiss, Crackle, and Pop

[Richie Burnett]

Cool, Tom.  I like the idea of generating noise on three different time 
scales and then shaping the spectrum of each before mixing them together. 
I've always wondered about designing a circuit that would simulate "vintage 
vinyl surface noise".  This comes very close, but doesn't quite nail the 
surface noise sound that I can hear in my mind.  Maybe my vinyl nostalgia is 
a bit off ;-)

There's a fair bit of 50Hz mains hum and it's harmonics in there too from 
what I can hear! ;-)

Did you think about possibly doing the whole thing in dsPIC software 
(noise+filtering+envelopes+mixing) ?  I was just thinking that a "hiss, 
crackle, pop" circuit is probably one of the few things that the dsPIC's 
built-in DAC would be ideally suited to (>.<)

-Richie,

-----Original Message----- 
From: Tom Wiltshire
Sent: Saturday, April 01, 2017 1:28 PM
To: Synth DIY
Subject: [sdiy] Hiss, Crackle, and Pop

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


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