Accordion -> MIDIbox SID

MIDIbox SID
1

No, you read the title right :slight_smile:

So, I have one of these Roland Virtual Accordions. An fr-3x, to be specific. It’s basically a keyboard with a bellows attached, bass buttons and integrated sound system. It also has MIDI output. All in all, it’s an abomination on all that is good and holy about accordions.

And I was wondering how I might make it play SID sounds, and considered briefly making sound sets to load into its registers. But this seems to be a strangely underdocumented feature. It would also be a terribly inflexible way of doing it. Then I thought “with all the crazy stuff people are still doing with C64 hardware, surely someone has built a MIDI syntheziser with the SID chip”. And here I am.

For this purpose, I want to build either a fairly simple MIDIbox with one or two SID modules, or maybe simply a sammichSID (assuming there are more kits available).

I just have a few questions before I start hunting for parts/kits (please forgive me if you’ve seen some of them before, or if they seem stupid):

  1. One of the points of the digital accordion is that by default, volume is affected directly by bellows pressure. And in the MIDI signal, bellows pressure is expressed through the CC11 (control change 11) channel. With a MIDIbox SID, how hard would it be to make CC11 affect volume for instance? (Or other properties of the waveform, come to think of it). Are these kinds of mappings a standard feature of the available software?

In case it’s not, could I do such tricks by modifying it, or writing my own software?

  1. I still haven’t understood the MIDIbox SID completely: The SID chip has three channels. How does this work in connection with MIDI input? Are MIDI instruments just mapped to SID channels? And what happens then if you send multiple notes on a channel simultaneously (i.e., try to play a chord)? Does it play only one note, or can it do some clever switching to make it sound like all the notes are played at once?

  2. Somewhat related to 2: The treble keys and bass keys of the accordion are treated as two different MIDI instruments. Would it make sense to have two SID modules, and dedicate each to one instrument. If simultaneous notes can’t be played on a single SID channel, this would in theory make it possible to play chords for instance, by using the three channels on each chip. Alternatively, maybe all three channels could be mixed to create more interesting sounds for the instruments?

I’m most curious about the first question. It would feel somewhat pointless to hook up a digital accordion if I can’t at least affect the volume with bellows pressure.

2
  1. One of the points of the digital accordion is that by default, volume is affected directly by bellows pressure. And in the MIDI signal, bellows pressure is expressed through the CC11 (control change 11) channel. With a MIDIbox SID, how hard would it be to make CC11 affect volume for instance? (Or other properties of the waveform, come to think of it). Are these kinds of mappings a standard feature of the available software?

The SID volume can only be controlled with 4 bit resolution, in addition you will notice a crackling sound (which was mis-used in the past to play samples)

So, controlling the volume is no suitable option.

You could control the cutoff frequency though. Or an external VCA controlled via an AOUT module (-> expensive, but you asked for this)

In case it’s not, could I do such tricks by modifying it, or writing my own software?

Currently CC#11 isn’t assigned to any parameter (for good reasons, because controlling the 4bit volume could be annoying), but you could do this in src/sid_cc_table.inc

  1. I still haven’t understood the MIDIbox SID completely: The SID chip has three channels. How does this work in connection with MIDI input? Are MIDI instruments just mapped to SID channels? And what happens then if you send multiple notes on a channel simultaneously (i.e., try to play a chord)? Does it play only one note, or can it do some clever switching to make it sound like all the notes are played at once?

If you are using the Multi Engine, the note stack allocation algorithm will cleverly assign voices automatically like a polyphonic instrument :slight_smile:

  1. Somewhat related to 2: The treble keys and bass keys of the accordion are treated as two different MIDI instruments. Would it make sense to have two SID modules, and dedicate each to one instrument. If simultaneous notes can’t be played on a single SID channel, this would in theory make it possible to play chords for instance, by using the three channels on each chip.

The multi engine allows you to assign voices to different MIDI channels, so that no second MBSID is required.

E.g. you could assign the three voices of the “left channel SID” to MIDI channel #1, the other three voices of the “right channel SID” to MIDI channel #2

Alternatively, maybe all three channels could be mixed to create more interesting sounds for the instruments?

Thats possible as well, the Multi Engine is very flexible!

Best Regards, Thorsten.

3

Or an external VCA controlled via an AOUT module (-> expensive, but you asked for this)

You know, it is a bit expensive, but if you are an accordionist looking at this type of thing, you would probably do very well to spend a few bucks and do this. You could control an external VCA right from MIDIbox SID, or you could control it using a separate MIDIbox.

You would gain the ability to control anything analog with your bellows! A VCA, a VCF, a pair of VCAs (bellows-controlled panning?), the brightness of an LED, PWM on a VCO - a lot of really interesting opportunities here.

4

The SID volume can only be controlled with 4 bit resolution, in addition you will notice a crackling sound (which was mis-used in the past to play samples)

So, controlling the volume is no suitable option.

I did wonder if the ‘crackling bug’ would be a problem. A fix for that might be to simply use an 8580 or 6582 chip (where that bug was mostly fixed, as I recall. To the great annoyance of many). I could probably get my hands on one of those.

And 4 bit resolution could maybe work, but yeah, it would certainly be noticeable.

You could control the cutoff frequency though. Or an external VCA controlled via an AOUT module (-> expensive, but you asked for this)

I’m not actually that much of a musician or hi-fi guy, so I just had to look up what a VCA was :slight_smile:

Certainly sounds like a much better solution. I’ll have a look at getting one when I’ve finished the MIDIbox. Do you have any good suggestions?

If it’s just somewhere below $400, I don’t mind so much. But I may get queasy if it goes far above that.

Alternatively, it sounds like something that could be DIY built for simple functionality.

Currently CC#11 isn’t assigned to any parameter (for good reasons, because controlling the 4bit volume could be annoying), but you could do this in src/sid_cc_table.inc

Thanks. I’ll probably try this with the volume, just to hear for myself if it really sounds that bad. But the prospect of affecting other parameters is interesting…

Thats possible as well, the Multi Engine is very flexible!

It certainly sounds exactly like what I want :slight_smile:

Well. Then there’s “just” the practical stuff left. I was considering a sammichSID kit, but if these only exist in limited supply, it’s probably best to leave them to someone else. I should be able to handle the building of a MIDIbox, and I’d prefer to have the complete control surface anyway. I even have a non-functioning C64 that I have no problem cannibalising for a case.

For me, the greatest issue seems to be how to make the front panel. It doesn’t seem possible to order them finished. And working in metal or plastic doesn’t appeal much to me.

But maybe a plain wooden panel would work? And then I could simply burn the labels into the wood by hand… This might even end up looking quite nice, if a little primitive.

But hey. SID _is_ technology from the eighties, so…

I’ll start by finding most of the necessary components/kits, and do some more reading. Then at the end of july, I’ll be at a summer camp for a week with likeminded geeks, and likely access to better equipment. With any luck, I can at least get a core module with LCD running then.

Many thanks. I’ll be back later, complaining about all the problems I will surely have!

5

Good luck with this. Every so often someone comes up with an idea like this and I’m desperate to see how it turns out. This is one of those times. Please keep us up to date with progress.

6

Good luck with this. Every so often someone comes up with an idea like this and I’m desperate to see how it turns out. This is one of those times. Please keep us up to date with progress.

Don’t be too impatient. I’ll do what I can, but it’s likely going to take a while. I’m a computer scientist by vocation and have done very little in electronics the past many years. And what I have done was mostly digital circuits. I find those easier to understand :slight_smile:

I am also not a great accordionist yet. I only took it up again recently, after having been without accordion for about 15 years. But I’ll get better, I’m sure.

I’m just a little afraid that by connecting a digital accordion and a MIDIbox SID, I will inadvertently concentrate so much awesome in one place that it collapses into a black hole and destroys the world. But it’s a risk worth taking, I think.

Anyway, I’m still evaluating my options:

On the VCA suggestion, I found some additional information here:

http://www.mhennessy.f9.co.uk/preamp/analogue_research.htm

So a digital potentiometer could perhaps also work. But for this part, I think I would still prefer some kind of boxed, premade solution, even if that’s going to be somewhat expensive. We’ll see. I know it’s possible now, so I’ll just have to build the midibox with an AOUT module and take it from there.

On the MIDIbox SID itself (I’m going from this, mostly: http://www.ucapps.de/midibox_sid_manual_hw.html ):

The sammichSID is likely out of the question, as it doesn’t seem to have an AOUT module.

The MB-6582 looks interesting, but also a bit overkill-ish. I don’t need 8 SIDs for this purpose. 2 should be sufficient.

There seems to be a number of extra modules involved in building the complete control surface, so I’ll start with the minimal one, since I really just need the ability to set up two “SID instruments” for the accordion.

Theoretically, I can just extend the control surface later if I want, by adding modules, and drilling more holes in the front panel :wink:

But the C64 case might turn out to be too small or constrained in the end. At least if I start extending with more modules. But I have a SparcClassic case which should be big enough for it, and future extensions (I am steadily cranking up the old-&-obscure-hardware-o-meter now).

So it looks like it will be a modular setup, starting out with the following:

1 Core module.

2 SID modules. (For bass and treble instruments from the accordion)

1 AOUT module. (For bellows pressure indication to some external amplifier. Alternatively, for a digital potentiometer maybe a DOUT module could do the job. But I don’t think anything prevents me from having both, really.)

A minimal control unit/surface (DINX2 module and various other stuff)

This would put the two SID modules in a “stereo” configuration on the same core, even though they wont really be used like that. But I am getting the sense that this simply makes the use of the two SIDs more flexible. It also saves me from having to build two cores :slight_smile:

Yees.. I think I can do this.