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The sixtyforgan

The sixtyforgan is a Commodore 64 equipped with a spring reverb, featuring the keyboard layout of a chromatic button accordion.


Echoes from the past

Back in 2008 I had an epiphany about church organs: At least in theory, organ pipes produce very simple waveforms, much like 8-bit sound chips do—and the reason church organs don't sound like chiptunes is primarily because of the acoustics of the church. I released an album called Reverberations where I programmed a Commodore 64 with organ music, and added enough reverb to make it sound like a church organ. But this wasn't live.

Then, in 2010, I created the Chipophone by gutting an electric organ and putting my own 8-bit synthesizer inside, so I could play video game music live.

Inside that organ was a spring reverb tank. Since I had no use for a reverb effect in the Chipophone project, I disconnected the tank, but left it mounted on the inside wall of the enclosure. From Making the chipophone:

Time will tell if I ever get around to doing this, but it bugs me that I have a perfectly good spring reverb tank just laying around.

It took me a decade, but the idea eventually resurfaced. Events that took place in 2010, 2008, even 1685, still reverberate.

Button layout

The keys on a qwerty keyboard are not arranged in a rectangular grid; the rows are staggered. This is because on a mechanical typewriter, each key is connected to a lever, and the levers are mounted on a common axle.

A chromatic button accordion solves the same mechanical problem in more or less the same way. Each key is connected to a lever for controlling the valves of that particular note across all the different registers. Accordion keys don't have to withstand the same force as typewriter keys, so the levers can have slight bends and turns, but the general principle is the same.

The button layout is highly regular: When you go from left to right, the pitch goes up by three semitones. When you go diagonally down and to the right, the pitch goes up by one semitone. Simply extend this pattern as far as possible in all directions:

Button layout diagram.

On an interesting side note, this means that if you go diagonally up and to the right, the pitch goes up by a whole tone.

The whole pattern repeats vertically, so you only need a minimum of three rows of buttons. A full-size accordion will usually have five rows of buttons, since the redundant rows provide more fingering options. A qwerty keyboard has four rows which is a good compromise.

Because of its regularity, this system is quite easy to learn. If you know the shape of a particular chord or scale, you can automatically play the same thing in another key just by moving your hand. (Five rows make this possible for every combination of musical motif and key; with four rows, you have to learn at most two different fingerings. The proof of this is left as an exercise for the reader.)

I can't stress enough what a brilliant system this is. On the piano, the C major scale is easy to learn, because it's made up of just the white keys. But then you have eleven more major scales to learn, and those are all different; they all have different fingerings. Now, I love the traditional piano layout because I grew up with it and feel very much at home with it. And yet it seems like a huge design flaw that you have to learn eleven complicated things by heart just so you don't have to learn the twelfth.

But it wasn't a flaw in the old days. Before the prevalence of equal temperament, chromatic transposition was practically useless, so designing a keyboard around it would have seemed ludicrous. Decisions and ideas from the past are still lingering today. We should savour those echoes from the past, but also transform and recombine them in new and fanciful ways. By adding our own tone colour, we become a part of their reverberation.

Posted Sunday 28-Mar-2021 22:13

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Mon 29-Mar-2021 03:38
simply superb!
Mon 29-Mar-2021 11:21
Hi Linus,
i would like to try that out myself.
I have a 6 voice c64 and a spring reverb from an old organ too.

Still waiting for the code of the Chipophone too ;)

most of us are not as good with Assembler and Maschinencode as you ^^"

kind regards from Germany Lara
Tue 30-Mar-2021 13:45
May I ask which waveform you chose for the organ? Is there a modulation or combination? Just asking for a friend..
Tue 30-Mar-2021 14:00
This has just made my day. The most bonkers thing I've seen in ages, and an utter delight. Thank you so much for sharing - I'm still giggling now!
Tue 30-Mar-2021 14:28
Having played with Hauptwerk this suddenly makes ~£500 plus another ~£200 for an instrument look quite expensive!

Brilliant demonstration that us choristers all knew! A generous acoustic hides a multitude of sins and just makes everything sounds much better.

Super demo and project!
Going to read up on this reverb device!
Wed 31-Mar-2021 16:39
wonderful project, very very well explained! Is the C64 playing program available for download? I made a similar program but for piano-like keyboard
Thu 1-Apr-2021 08:38
Can't you eliminate ghosting in software by verifying keypresses by lighting up different parts of the matrix?
Thu 1-Apr-2021 11:46
I like everything about this, but I do love how you casually quoted the Amiga Basic "Music" demo in the first video :)
Thu 1-Apr-2021 12:42

LaraCraft wrote:

i would like to try that out myself.

Me too!
Thu 1-Apr-2021 13:17
Thankyou for doing this - it's fascinating, the device really sounds like a big church organ. I've built a Z80 single board computer, and after hearing this, I want to try connecting a sound chip to it, and then tweak the output wave. I have this big Teac reel-to-reel tape recorder, and I recall creating a "reverb" affect with it by feeding playback head output back into record head. But using the electromechanical reverb unit is genius - you get a complex polyphonic sound that renders Bach very nicely. -MCL, Waterloo, Canada.
Mon 5-Apr-2021 23:22
I'm really impressed!
Wed 7-Apr-2021 11:08
Quote of the day:
"I didn't have a cathedral at home but I did have this spring reverb tank"

Also, it would be fun to hear the sixtyforgan without reverb tank in an actual cathedral. Maybe you should visit Reyn?

Sat 10-Apr-2021 18:39
I am posting here so you will see this comment. I would like to tell you that "Autosokoban" is broken. The link for level seeds no longer work, and they don't load up.