My first major Propeller project

PaulForgey

I've mostly completed my first major hobby project using the Propeller. Although the Propeller is not a DSP, I was curious to see how far I could get with an FM synth project. The result is a 8 note polyphonic, 4 operator, 12 algorithm standalone FM synth with a VGA UI and MIDI controlled input.

I started it with the motivation of trying to push the things as far as I could, and I'm sort of pleased with how it turned out. The code and circuit description is on GitHub.

I actually don't do DSP work in real life, and if somebody who does takes some interest and has feedback, it would of course be greatly appreciated!

https://github.com/PaulForgey/spinSynth

T Chap

Congrats, sounds like a fun project. Youtube audio samples?

PaulForgey

My keyboard skills are about that of a first grader with a month of lessons . I'll find a good MIDI track I can send it

T Chap

No keyboard skills needed to press middle c.

Mickster

PaulForgey wrote: »

My keyboard skills are about that of a first grader with a month of lessons .

IOW, today's pop music level? That's fine

Chris Savage

LOL @ Mickster

JLS

Hi Paul

This is very interesting project.

Is possible make library for independent use like SIDCOG, AYCOG ?

Many thanks

Kamil

PaulForgey

@JLS I tried to keep the components usable as they are without too much infrastructure around them. Some things need a bit of work, e.g. the envelope generator makes a few strange assumptions but it mostly generically useful. The oscillators are very usable standalone and could be worked into almost any sort of FM synthesis scenario.

I'm not trying to emulate anything in particular, although I did use my knowledge of the DX7's internals as a general guide how to structure the overall project.

JLS

Thanks info about project.

But im very bad programmer is possible make simple example how to generate sound ? (project is very complex for me :-) )

Many thanks

PaulForgey

I'm currently working on completely re-doing the mess I've made of the envelopes. After that, I'll put together a high level document giving an overview to how all the pieces work. I've tried to document things inline at the component level.

PaulForgey

JLS wrote: »

Thanks info about project.

But im very bad programmer is possible make simple example how to generate sound ? (project is very complex for me :-) )

Many thanks

Envelopes are a rather critical piece of the puzzle, but this shows how to minimally make noise using some of the components. If you want to make use of the envelopes, the most critical thing about them is they need to have their 'Advance' method called as an idle process.

CON
    _clkmode = xtal1 + pll16x
    _xinfreq = 5_000_000
    
OBJ
    osc     : "synth.osc"
    out     : "synth.out"
    
VAR
    LONG    TriggerPtr
    LONG    AudioPtr
    LONG    Inputs[8*4]
    LONG    Envelope[5]
    BYTE    Algo
    BYTE    Feedback
    
PUB Main | v
    ' start oscillator cog. This provides 8 oscillators/2 voices
    ' leave Algo and Feedback set to 0 for organ mode (all oscillators output, no modulation) and no feedback
    osc.Start(@Inputs, @Algo, @Feedback)

    ' array of one element for audio outputs and triggers
    AudioPtr := osc.OutputPtr
    TriggerPtr := osc.TriggerPtr
    
    ' output cog also drives envelopes. Even if we don't need them.
    ' must provide at least one envelope set (5 longs each)
    ' we have one set of audio/triggers
    ' output to pin 9
    out.Start(9, @AudioPtr, @TriggerPtr, 1, @Envelope, 1)

    ' play a C   
    Inputs[0] := $6132
    ' 0 = full output (no attenuation)
    ' $8800 is silent, log scale
    Inputs[1] := 0

JLS

Many thanks example working :-)

PaulForgey

cool! I hope to have an overview document added to the GIT repository shortly