Midi Omnichord

[Dimitree]

hello everyone :)

I'm trying to understand how the Suzuki Omnichord works

this is a schematic:

 

https://doc-10-8c-docs.googleusercontent.com/docs/securesc/lk54a81tnkfa15utnl5v22uglsogf3ls/nqti4dgff7k1rilokqh8irq5j6646enh/1363003200000/02641102607401280949/03078043583709180525/0B8-MOD-DNXkHZGE3NmU4NzctZDhkYi00Njg0LWIwMmQtNjQ3ZDJjZDAxNzk4?nonce=ds9rb1d857csm&user=03078043583709180525&hash=jke3063mf4b7k81s36scpsah1vhcbc2l

 

Since I think it's a pretty simple device, I was wondering if I can build its tone generator around Midibox. The "Midibox side" (I mean chord generation, control program, etc) is not a problem for me since I'm a programmer, but I really can't undestand how this thing can do sounds.

 

Looking at the schematic those are my guesses:

the main CPU monitors the switches to decide which chord to output. Then there's a 8253 timer chip that should be able to output square waves tones. The output is sent to some dividers (upper-right on the schematic) that I don't undestand at all what are doing. There's then a circuit (on the center-right of the schematic) that makes the drum sounds (I can skip this part, I don't need it at all).

Last, on the bottom part of the schematic, there are 13 touch sensor that trigger the notes, then the amplifier and the power supply.

Looks like the sound generation is digital, the 13 triggers are only there to activate the right note coming from the digital chip.

Replacing the main CPU with a midibox should be fairly simple, but what about the tone generation?

 

Now since I have Omnichord samples, I can't undestand how this schematic can make such waveform (at the lowest note), and then become a triangle-like waveform at the highest notes.