[sdiy] Re: FPGA 2-OP FM MIDI Polysynth

[Richard Wentk]

On 4 May 2009, at 18:56, Veronica Merryfield wrote:

> My suggestion is to have each unit with a fixed frequency input, an  
> envelope and an input from another unit. The unit is just a sine  
> oscillator followed by an amplitude modulation stage controlled by  
> an envelope and perhaps another input. This is followed by an  
> accumulator where the output of this and other units can be  
> gathered to provide an input to other units.

This would be not unlike one of these:

http://knorretje.hku.nl/wiki/Sogitec_4X

> I further proposed for the envelopes that multiple linear stages  
> are used. Linear stages are much easier to implement digitally and  
> provide the user the facility to create exponent curve  
> approximations through the use of multiple linear stages. If the  
> user interacts with software rather than the raw data, the software  
> can make this task simple. The envelope mechanics also need a  
> sustain point or the ability to loop until the release. The looping  
> allows for volume of frequency effects (vibrator, tremolo, etc)  
> normally associated with LFO on an analog synth.

This how some softsynths solve the problem. In Max/MSP you have  
smooth control of envelope slopes from (piecewise approximations of)  
exp to lin to log.

It's a simple system and it sounds good.

Richard