[sdiy] Hiss, Crackle, and Pop

[Tom Wiltshire]

On 1 Apr 2017, at 18:53, Neil Johnson <neil.johnson71 at gmail.com> wrote:

> Hi Tom,
> 
>> 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…
> 
> A few years ago a friend of mine (top-notch DSP engineer with an
> interest in audio) developed a DSP system for recreating the sound of
> 78s (I gather it was a homer project in between designing DSP code for
> satellite comms).  It had everything you could imagine - wow&flutter,
> scratches, hiss, and so on.  It was very convincing.  Not sure where
> it went, but suffice it to say that doing it right is a lot lot lot
> harder than it seems...
> 
> Neil

Hohoho! Yeah, I bet! You could definitely throw a pile of hardware/software at the problem.

I had several ideas for extending my basic version - lowpass filtering a noise output to give a wandering CV, and then sing that to control the volume of the other channels. Obviously this could be repeated several times for several channels…
I also think that two channels is still sufficiently simple that your ear can differentiate them. If there were three or four or five, I think you'd get a noticeably  richer effect.
It might also be fun to build a version with knobs on. Each channel could have  a"frequency/probability" control for the basic rate the events occur, a "decay" control for the envelope, and then "lowpass" and "high pass" filter knobs. Resonance would be a nice touch too. Several channels of that would enable you to mix up many flavours of noise.

There's a certain overlap with some other experiments I've done. One is a "granular oscillator" that I wrote as an alternative code load for Bruce Duncan's Modcan AHDBDSR envelope generator. That had raised-cosine-enveloped pitched grains, and you could alter the randomness of the pitch , start point, and the frequency of the grains in the grain cloud. It produced a range of textures from sputtery/spattery to rainy to sizzly.
The other area that this borrows from is analog percussion synthesis. I borrowed Roland's VCA, but the basic idea of a blast of shaped noise with a tone filter is the guts of many a drum machine sound. This suggests other interesting directions, like trying alternative sources like the "Metal noise" combinations of CMOS oscillators used for cymbals, either XOR'd or not as the mood or your vintage inspiration take you.

So…yes, I can definitely understand how they might have spent quite a lot of time and DSP power on the problem!

Tom