[sdiy] Hiss, Crackle, and Pop

Mon Apr 3 17:43:50 CEST 2017

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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