[sdiy] Hiss, Crackle, and Pop

Mon Apr 3 19:51:53 CEST 2017

I need to finish designing and building the Organ Donor module first, but I
would love to have one of these hiss, crackle, and pop chips! At the rate
I'm going, I won't have to buy any pre-made modules for my rack. :)

On Mon, Apr 3, 2017 at 12:44 PM, Tom Wiltshire <tom at electricdruid.net>
wrote:

> If you find another several dozen people who feel the same way, sure! ;)
>
> Unless there's a lot of interest, I won't bother getting pre-programmed
> chips sorted out, but I've got no problem programming the odd one for
> anyone who asks nicely.
>
> Tom
>
> On 3 Apr 2017, at 16:43, Elain Klopke <functionofform at gmail.com> wrote:
>
> Hey Tom,
>
> Does saying so here count as emailing you? Can we see these chips in your
> shop?
>
> On Mon, Apr 3, 2017 at 10:37 AM, Tom Wiltshire <tom at electricdruid.net>
> wrote:
>
>> Thanks. It does have some high pass, but you might be right that more
>> would be better. I've got it on the breadboard, so I'll give it a try.
>>
>> It's an "adjust to taste" circuit really - you could do a lot of tweaking
>> in terms of pop/crackle frequencies and tone.
>>
>> Since I posted it here, I've written it up and put it online:
>>
>> http://electricdruid.net/adding-vintage-hiss-crackle-and-pop/
>>
>> Tom
>>
>> On 3 Apr 2017, at 15:25, Amos <controlvoltage at gmail.com> wrote:
>>
>> If I might offer a small aesthetic suggestion, I think the "crackle"
>> channel might sound a lot better (er, more crackly) with a simple highpass
>> filter on it.  Very cool project. :)
>>
>> On Sun, Apr 2, 2017 at 12:25 PM, Tom Wiltshire <tom at electricdruid.net>
>> wrote:
>>
>>> I'm not sure how you'd synthesise the vinyl bump sound, but getting a
>>> periodic noise wouldn't be hard.
>>>
>>> If you used the same firmware in two H.C.P. chips and started them up at
>>> exactly the same moment, I suppose you might hear something, since they
>>> follow the same LFSR pattern. However, it would be easy to change the
>>> random seed in one of the chips at programming and then they'd follow
>>> completely different paths. The LFSR is 47-bit  so doesn't repeat for 2^47
>>> bits. It's running at 90KHz or so, and I calculate it a byte at a time, so
>>> that brings it down to 2^44, but it's still a vast number and a long repeat
>>> time - over 6 years. Set one at a different point in the pattern and they
>>> could well be 18 months apart.
>>> The other significant fact is that the chip uses the internal RC
>>> oscillator not any external crystal so even if they started in sync they
>>> won't stay that way for long. The two sets of sample outputs will be close
>>> to the same rate, but they'll drift in and out. That means there'll be no
>>> relationship between when the random crackles and pops occur on the two
>>> chips, even at the sub-millsecond level we're talking about.
>>>
>>> Tom
>>>
>>>
>>> On 2 Apr 2017, at 16:19, Mike HEQX <mike at heqx.com> wrote:
>>>
>>> > Tom,
>>> >
>>> > That's a great idea, but my synths do this on their own LOL
>>> >
>>> > If you wanted a cyclic bump like on vinyl what would you need to do?
>>> Could this thing drive a timer externally? If you had two of H.C.P working
>>> together would it create any type of convergence that might sound like
>>> something periodic?
>>> >
>>> >
>>> > Mike
>>> >
>>> >
>>> > On 4/1/2017 3:02 PM, Tom Wiltshire wrote:
>>> >> 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
>>> >>
>>> >>
>>> >>
>>> >>
>>> >>
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