YES! Someone finally used the audio-in pins!

The SID has audio-in that can be summed with internally-synthesized sounds and routed through the on-chip filters before going back out.

I found this pinout in the programmer's reference guide and tinkered with it a bit as a kid, but I didn't really know what I was doing, so it never went beyond a novelty. Who knew, forty years later, that it'd get proper treatment as an effects generator!

Thanks for explaining - I had no idea there were audio in pins, and was searching the page for how they managed to route audio to the SID without any modification.

Warning to the curious: it is very easy to fry your SID connecting directly to the audio in (don't ask how I know this). Make sure of your levels before you connect, and don't plug this in with the power on in case there's a short.

Is this still the case with recent audio hardware? I was under the impression that a typical instrument's output levels are far too low to cause any damage and that all inputs would be surge protected.

> don't ask how I know this

Tease!

I also know this.

In my defense, I was like 9 at the time and didn't know about AC-coupling for audio signals yet. That smoked SID is still down in my basement somewhere, I wonder how much of it still works.

any suggestions to protect it? e.g. buffer with an op-amp, right? Any way to use diodes for static protection, etc.?

One common way to provide input overvoltage protection is through a pair of schottky diodes. This article is a good resource https://www.digikey.com/en/articles/protecting-inputs-in-dig...

That's a pretty good article. Also, the classic one-volt-or-so voltage limiter is a pair of antiparallel silicon diodes. You can put them in series for a bigger limit.

There are some good practical solutions here ( https://www.lemon64.com/forum/viewtopic.php?t=55483&sid=2710... ) but the most important thing is keep the voltages down. They suggest three volts max peak to peak, which seems prudent.

This is fantastic, but I wonder how could I miss it in the old days. I had the full C64 reference manual and all I found was an audio in that could only turn on and off the incoming signal, which of course was a lot less fun than letting it through the SID filters; was it a different input? I'm not sure I used the DIN connector though, I probably interfaced to the user port; can't remember.

I think Machinae Supermacy band does this: https://www.youtube.com/watch?v=XKkmyMKbPKE

... or emulate the whole thing using a free VST plugin.

(shameless plug)

Find the right garage sale and the C64 is a free plugin =D

It makes me want a guitar and a C64!

One thing to note about a wah-wah pedal[1] if you ever want to simulate it in software is that if I understand it correctly it’s a parametric equalizer and when you wobble the peddle you are affecting the Q (bandwidth) of the equalization. You can hear this for yourself if you use a normal mixing desk, just play something, set a reasonable boost to some mid frequency on the parametric eq and wobble the Q backwards and forwards. You basically get the effect of the pedal.

[1] And it has to be a “wah-wah”, not “wah”.

This is incorrect.

When you move the wah pedal, you're moving the cutoff of the filter, not the Q. The Q is fixed.

You're also incorrect about the name. Just 'wah' is perfectly acceptable.

Wikipedia has it as “wha-wha pedal.”

https://en.m.wikipedia.org/wiki/Wah-wah_pedal

Because of the Wha-Wha (or Wa-Wa) effect.

https://en.m.wikipedia.org/wiki/Wah-wah_(music)

All true, but Wikipedia is just a reference, not an authority, right? “Wah” and “Wah Wah” are both fine. I assume the “Wha-Wha” spelling you used is autocorrect or accident?

Shopping online it looks to me like “Wah pedal” is more popular than “Wah-Wah pedal”. Here’s a pile of examples of guitarists using “Wah pedal”: https://www.sweetwater.com/c976--Wah_and_Filter_Pedals https://www.guitarcenter.com/Wah-Filter-Effects-Pedals.gc https://www.guitarworld.com/features/best-wah-pedals https://www.bestreviews.guide/guitar-wah-pedals https://www.musicradar.com/news/the-best-wah-pedals

Literally the first sentence of your first link:

"A wah-wah pedal, or simply wah pedal"

> And it has to be a “wah-wah”, not “wah”.

this is just not true. guitarists regularly call it either. i hear it called a “wah” more often these days than “wah-wah”.

anyone will clearly understand and not look at funny if you say “wah pedal”