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Hardware projects

The sixtyforgan

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

Download

  * Linus Akesson - Sixtyforgan - Ich ruf' zu dir.mp3 (MP3, 2.6 MB)

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

Discuss this page

Disclaimer: I am not responsible for what people (other than myself)
write in the forums. Please report any abuse, such as insults,
slander, spam and illegal material, and I will take appropriate
actions. Don't feed the trolls.

Jag tar inget ansvar for det som skrivs i forumet, forutom mina egna
inlagg. Vanligen rapportera alla inlagg som bryter mot reglerna, sa
ska jag se vad jag kan gora. Som regelbrott raknas till exempel
forolampningar, fortal, spam och olagligt material. Mata inte
tralarna.

Anonymous
Mon 29-Mar-2021 03:38
simply superb!
[Report abuse]
[Quote & reply]
LaraCraft
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
[Report abuse]
[Quote & reply]
Anonymous
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..
[Report abuse]
[Quote & reply]
Anonymous
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!
[Report abuse]
[Quote & reply]
Anonymous
Tue 30-Mar-2021 14:28
Having played with Hauptwerk this suddenly makes ~PS500 plus another
~PS200 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!
[Report abuse]
[Quote & reply]
Anonymous
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
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