[sdiy] VC ADSR

[jbv]

Hi,

Ahem... Don't you think that even a simple hand-made
schematics would speak better to newbies like me...

Anyway; VC morphing of LUT values is pretty
straightforward with a uC : no extra hardware, and only
a few instra lines of code...

JB


> hello ppl
>
> > This is something I've been brainstormin on lately :
> > I decided to use a uC and LUT to generate log / lin slopes,
> > and even parabolic & other exotic shapes...
> >
> > I've even considered VC-morphing between those slopes.
> > This is feasable via software, but the downside is the number
> > & type of controls to make it easy to use : the front panel of each
> > VCADSR would feature more pots than the rest of the modular...
>
> VC morphing is much more feasable if your doin' it completly
> analog . Simple brute force solution : lets asume control inputs
> of vcadsr accept 0-5V CV and that you have 0-5V morph CV .
> Make one unity gain inverter with opamp and feed morph CV to it .
> Note output of this opamp as CV1 . Make inverting unity gain
> summing amp with two inputs . feed one input with CV1 and
> other input with consatant 5 volts . Note output of summing amp
> as CV2 . Make inverting unity gain summing amp with two inputs
> and use lets say 1k resistors for it . Take two 1M pots and
> conect one between one summing input and CV1 and other
> between other summing input and CV2 ( ! pots are used
> here as variable resistors not variable voltage dividers ,
> therefor one leg of pot is left unconnected ) .
> These two pots will give you Attack1 and Attack2 values .
> Make same pots+summing amp arangements for decay , sustain
> and release . Feed outputs of summing amps to coresponding
> VC inputs of ADSR . Now you can with morph CV make
> continous changes between two sets of values for A,D,S and R .
>
> As for parabolic , you only need linear AD envelope generator
> and simple sine shaper as one from VCOs ( cos uncle Fourier
> will tell you that a-x*x is very very very close to cosx
> for segment -Pi/2<x<Pi/2 ). And better yet , you could
> normaly change A time and D time and thus make
> assymetrical parabolic envelope . Or you can feed
> complete adsr to sine shaper or you can feed env or lfo
> to full wave rect. or trough DC coupled state variable
> filter . This is what modular analogs are all about .
> Modelling nonlinearity in analog domain by actually
> solving some math equation by circuit is very wrong aproach .
>
> And finaly , i think there should be no problem at all
> with switchable lin/log envelope . If we look at env generator
> it can be simplified as follows : you feed some sort of gate
> signal to either first order LPF and you get log ( or
> should I say "log" ; why the hell people call this
> log when all segments are desribed with expo function )
> or feed it to integrator and you get linear segments .
> So we need something that acts as VConepoleLPF or
> (one switch away) VCintegrator . We actually do have
> such circuit . Take a look at first order cell in
> SSM2040 . It is integrator with unity gain feedback around
> it wich turn it into first order low pass . You just
> need switch that cuts feedback path and you have
> core element for lin/log vcadsr .
>
> regards
> urosh
> (have done complex integrations all morning on horrible math exam)