[sdiy] Cheapest, simplest but still reliable VCO & VCA for polyphonic project

[Tom Wiltshire]

On 9 Jan 2009, at 06:17, Antti Huovilainen wrote:

> On Fri, 9 Jan 2009, George Hearn wrote:
>
>> Believe me I would love to cut corners in components and cost but  
>> sound is paramount to me, LFO's can be digital, but not env's.
>
> Why not?
> It's not that hard to get 1 kHz update rate for envelopes which  
> should be smooth enough (with RC smoother per cv output) and fast  
> (minimoog can get about 1ms attack time and is generally considered  
> to have one of the fastest attack times).

This is one of those areas where opinions differ! I talked to George  
about it at the Synth DIY UK gathering in July. He's a hardcore  
analogophile in this regard, although I'm still hoping to win him over.

The digital Quad Env I coded for Bruce Duncan/Modcan used a 25KHz  
sample rate and could output around 20 samples for even the shortest  
(sub 1 mS) curve. In my opinion this is entirely indistinguishable  
from analogue in use. The other benefits (more stages are possible  
with no further circuit complexity, various envelope curves are  
easily selectable) also swing the balance for me definitively in  
favour of digital envelopes.

They got a bad name back in the days when people were using one 68000  
or similar to produce all the envelopes for an 8-voice synth,  
whereupon the update rate finishes up being in the hundreds of Hertz,  
but nowadays that limitation is gone.

T.