Idea for a Prop based music board, for chip emulators and synthesizers
onewheeltom
Posts: 40
After spending some time with the PropSID emulation code designed by Ahle2, I have been thinking about a design for a Propeller based music/audio board. My main interests are in the C64 SID chip and electronic music. I also have an interest in modular synthesizers, but they tend to be very costly. I would like to build usable instruments based on these emulators...instruments that are designed in software but have physical controls that can be manipulated. Instruments that can be used by musicians.
My goals are as much creative as they are technical. I want to keep this relatively simple, but flexible enough to be used for different purposes. For example, a Prop based SID synthesizer or something like an emulation of the EMS Synthi A :
http://en.wikipedia.org/wiki/EMS_Synthi_A
One can still purchase a Synthi A, but they cost between $7,000 and $12,000.
Something similar to this was described in a posting on the Parallax forums from 2010 :
http://forums.parallax.com/showthread.php?118285-SIDcog-The-sound-of-the-Commodore-64-!-(Now-in-the-OBEX)&p=948744&viewfull=1#post948744
The first project would be an add on board for the QuickStart. It will likely not conform to QuickStart dimensions, but could be attached with mounting hardware, and would likely include the following :
- 8 input analog multiplexer (like the MCP3208) for adding knobs or reading CV (control voltage). May want the option of soldering the pots directly to the board to create an "all in one" device.
- Board space for a 16 bit audio DAC, for higher quality audio out
- Midi IN and MIDI out - I may want to use the Prop to control MIDI devices in addition to controlling the Prop with MIDI devices.
- Audio Line out, perhaps a small chip amp. Maybe even a little speaker.
My goal is to create a basic platform design so that more time can be spent developing instruments. I also want this to be something that will be accessable to beginners. It would be nice to "normalize" some settings and pinouts to reduce initial frustration; make success more likely.
I have other ideas but would like to focus on getting something finished, making some boards, then moving on to another related project. PCB designs will be available for general use through some sort of open source license.
I look forward to your comments and suggestions.
--Tom
My goals are as much creative as they are technical. I want to keep this relatively simple, but flexible enough to be used for different purposes. For example, a Prop based SID synthesizer or something like an emulation of the EMS Synthi A :
http://en.wikipedia.org/wiki/EMS_Synthi_A
One can still purchase a Synthi A, but they cost between $7,000 and $12,000.
Something similar to this was described in a posting on the Parallax forums from 2010 :
http://forums.parallax.com/showthread.php?118285-SIDcog-The-sound-of-the-Commodore-64-!-(Now-in-the-OBEX)&p=948744&viewfull=1#post948744
The first project would be an add on board for the QuickStart. It will likely not conform to QuickStart dimensions, but could be attached with mounting hardware, and would likely include the following :
- 8 input analog multiplexer (like the MCP3208) for adding knobs or reading CV (control voltage). May want the option of soldering the pots directly to the board to create an "all in one" device.
- Board space for a 16 bit audio DAC, for higher quality audio out
- Midi IN and MIDI out - I may want to use the Prop to control MIDI devices in addition to controlling the Prop with MIDI devices.
- Audio Line out, perhaps a small chip amp. Maybe even a little speaker.
My goal is to create a basic platform design so that more time can be spent developing instruments. I also want this to be something that will be accessable to beginners. It would be nice to "normalize" some settings and pinouts to reduce initial frustration; make success more likely.
I have other ideas but would like to focus on getting something finished, making some boards, then moving on to another related project. PCB designs will be available for general use through some sort of open source license.
I look forward to your comments and suggestions.
--Tom
Comments
Sounds like an interesting and fun project. Good luck with it.
This would make for a much larger board than would be required by using a small board for the ADC chip and ribbon cable to connect the inputs to the pots. It would also make replacing pots difficult when they go bad.
Using small separate board for this would minimize any noise pickup caused by having digital circuitry on the same board.
With all the rotary pots, slide pots, and other controls required you will need a case that is large enough to fit several small module boards as well. They could connected with ribbon or audio cables as required. This will make the system easier to build and debug, as well as allowing it to be expanded with additional modules/functions in future.
It would be relatively simple to cut and paste the individual modules to make a single board out of the project at some future date.
I think it would look cool to have the pots sliding on their own as they play back recorded positions.
I don't know if they'd be a good fit for your project of not. SparkFun also sells these motorized pots with an audio taper.
The DAC and multiplexer will be on the separate board that is plugged into the Quickstart, which should help some with noise.
Should I put the DAC on one side of the QuickStart "bus" and the multiplexer on the other? Will that help minimize noise? Perhaps a large ground plane surrounding the analog inputs and audio outputs?
I thought back and forth about having the pots on a separate board. For a first pass, I think I'll put them on the same board close to the edge. I would rather have it "all in one" which may allow operation without a case. I can include pin headers in the layout that would allow the pots to be moved off the board. With the small pots I will likely be using, this shouldn't be a problem. Guess I'll find out. :-) Thanks for the feedback.
--tom
First of all I must say that I'm humbled by the fact that my sound chip emulators sparked your interest in the Propeller. It's really great for applications like this!
I think your project is a great idea and I have been pondering something similar but never got past square one.
At the moment I'm a little bit busy with work and private things, but as soon as things will settle a little bit I will join in.
http://forums.parallax.com/showthread.php?115258-TheBlackBox-Release-v2.0-Propeller-HSS-FX-Sequencer-with-Digital-Audio-SPDIF&highlight=blackbox
For best results when laying out a board with digital and analog circuitry try to keep the analog portion separate from the digital circuit. This is not always easy to do when both analog and digital signals are on the same chip. Try to avoid having analog traces run parallel to digital ones, place a ground plane around the analog section as you mentioned, and if you have separate analog and digital supplies connect the analog and digital power grounds together at one point only.
I've seen your PM and will reply asap. The old synthesizer doesn't exist anymore, but I'm building
a new one which includes the SIDcog. The current version is being re-written in C (Propeller GCC Compiler).
I suggest following components for a Control Panel (e.g. if using 64 potentiometers):
MCP3208 ADC (8 ch) , 8 x CD4051 Analog Multiplexer, Shift Register
Another possible solution is: Shift Registers + Rotary Encoders + Buttons
Cheers