[Fpga-synth] Envelope - linear attack & expo decay/release?

[Scott Gravenhorst]

Eric B. wrote:
>Here's a philosophical question:
>
>Last weekend I built an ADSR for my ARM/FPGA synth and it seems to work 
>fine. The thing that's bugging me is that I used linear calculations for 
>the gain, so when doing a long release that last little tail seems to 
>cut off rather abruptly.
>
>The obvious solution is to use exponential decay for the release. I know 
>how I'd implement that in hardware (scale the difference between where 
>you are and where you're going by some constant related to the rate & 
>add to current state). Question is, is the exponential curve also 
>appropriate for the attack & decay phases?
>
>The ultimate envelope would seem to be one with the option for 
>log/lin/expo curve on each segment, along with variable rate & target. 
>You'd need three parameters to define every segment. Probably too 
>complex, but certainly flexible.
>
>Thoughts? What have you tried in the past?
>
>Eric

I went back to my GateMan synths and they are linear only ADSRs.  They have the same
"problem" that Eric describes.

My question is: What envelope shapes are most useful?

How much does it matter that A and D are expo?

Would the most useful modification to an ADSR be simply selectable lin/expo for R?

-- ScottG
________________________________________________________________________
-- Scott Gravenhorst
-- FPGA MIDI Synthesizer Information: home1.gte.net/res0658s/FPGA_synth/
-- FatMan: home1.gte.net/res0658s/fatman/
-- NonFatMan: home1.gte.net/res0658s/electronics/
-- When the going gets tough, the tough use the command line.