
Analog computation, Part 1: What and why - hk__2
https://www.analogictips.com/analog-computation-part-1-what-and-why/
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mariefred
Maybe I'm old but that's common knowledge, the reason more and more
computations are moving to the digital world is weirdly the simplicity of
implementation and not accuracy, speed, price, reliability or anything else
super sophisticated.

It's much easier, faster, maintainable and usually cheaper to add a cheap
controller and peripherals than to find an electrical engineer to do the math
and design a circuit.

~~~
setquk
Actually it's usually better in the digital domain for all of those reasons.
Most systems these days have minimal transducer processing stuff in the
analogue domain and get it into the digital one as quickly as possible.

Analogue systems have a lot of non-ideal characteristics such as drift,
thermal sensitivity, parasitic capacitance and inductance, impedance matching
problems, insane cumulative errors and manual tuning requirements that don't
exist in the digital domain. They are also more expensive to modify, and the
price goes up significantly with complexity and speed. Not to mention small
and fast is really difficult in the analogue domain thanks to everything being
a transmission line.

~~~
jacquesm
> insane cumulative errors

Any sufficiently advanced analog computer is indistinguishable from a noise
generator.

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audiometry
Omega Tau podcast has quite a long episode on analog computers.

~~~
adyavanapalli
Episode link: [http://omegataupodcast.net/159-analog-
computers/](http://omegataupodcast.net/159-analog-computers/)

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Tade0
I still have a few operational transconductance amplifiers lying around which
I tried to use for my guitar effects projects(none of them ever reached
completion of course).

Not obvious to work with, but a great solution if you want to multiply two
signals.

~~~
atoav
Other ways to do this: \- Vactrols (a LED/LDR combination) \- Blackmer VCA
Chips (e.g THAT2181 or SSM2164) \- Analog Multiplier ICs (these are actually
four-quadrant multipliers), (e.g. AD 633) \- PWM switching \- ...

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bogomipz
The FAQ states:

>"Q: What are some of the issues associated with analog computation?

A: They are similar to the ones that are of concern whenever analog functions
(op amps and more) are used for signal processing or signal conditioning.
These include linearity, offset, temperature-related drift, aging, and
bandwidth."

I understand bandwidth but could someone elaborate in lay terms what these
other "concerns" are in analog circuits? Specifically what are linearity and
drift?

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pjc50
Linearity: if a system is linear you can draw a nice straight line on an X-Y
plot of input vs output. Nonlinearity is a measure of how much it deviates
from that line.

Drift: component values are not fixed! Most vary slightly with temperature,
and capacitors change value over time too. Can be seen in any kind of old
equipment which needs to "warm up".

~~~
bogomipz
Thanks for the wonderful and detailed responses. I really appreciate it.

One follow up - is it accurate to say that linearity and drift are always
related then?

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pjc50
Not really, they're separate parameters. Things like crystals and diodes are
subject to drift without being linear at all. And ADC/DAC designers worry
about linearity a lot while not being concerned about drift, because that gets
outsourced to the reference voltage.

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adamnemecek
They will come back in the form of continuous variable quantum computers.

~~~
jacobush
Distinct quanta ... variable?

