[sdiy] Hiss, Crackle, and Pop

[Tom Wiltshire]

Hi Richie,

Yeah, I was probably aiming for something about 30 years earlier than vinyl! But I know what you mean, that "old 78s" noise would be lovely. You could probably get closer with a bit of fine tuning of the circuit.

The mains hum…I dunno. I think it might be from recording the sample on the laptop with an unshielded cable. I should really have added a mains hum generator into the mix too, with a EU/US 50/60Hz selector!

And no, I definitely didn't think of using a dsPIC! A 16-bit processor to make the noise of old wax cylinders going round?! Are you crazy, man?!
No, I used a simple *8* bit processor for a job like that!! I even stayed away from op-amps because that just seemed too modern for the job. Maybe a 741 would be allowable.

But you're dead right - it's one place the background hiss on the internal DAC might even be a benefit…

Tom

On 1 Apr 2017, at 15:18, "Richie Burnett" <rburnett at richieburnett.co.uk> wrote:

> 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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