--- On Tue, 11/11/08, Gordon JC Pearce MM3YEQ <gordon@...> wrote:
From: Gordon JC Pearce MM3YEQ <gordon@...>
Subject: Re: [korgpolyex] Hawk-800 Feature Idea
To: korgpolyex@yahoogroups.com
Date: Tuesday, 11 November, 2008, 10:57 PM
Alex Drinkwater wrote:
> Hi.
>
> --- On Tue, 11/11/08, Gordon JC Pearce MM3YEQ <gordon@...>
wrote:
>
>> From: Gordon JC Pearce MM3YEQ <gordon@...>
>> Subject: Re: [korgpolyex] Hawk-800 Feature Idea
>> To: korgpolyex@yahoogroups.com
>> Date: Tuesday, 11 November, 2008, 10:12 PM
>> Atom Smasher wrote:
>>
>>> just add some velocity "accent" and you can
>> not just emulate a 303, but go
>>> beyond a basic 303 sound.
>> Bear in mind that a real 303 also slows down the attack
>> portion of the
>> filter envelope when accent is on, as you increase the
>> resonance.
>
> Ah.. I didn't know that...
> I thought the decay was reduced on accented notes, but I'd never have
twigged the attack was also slowed at the same time. I assume it's only the
filter attack that's altered, not the volume envelope.
Yes, the decay is reduced to minimum.
>> That's why the resonance pot has a double track - one
>> half provides
>> feedback around the filter,
>
> So the resonance-boost on accented notes isn't actually from the
filter circuit itself? Interesting...
I'm not sure that there ∗is∗ a resonance boost on accented notes - I
don't see anything in the circuit that would do that. There might be
something I'm missing though.
Don;t know why I assumed there was, really. Think I probably read it somewhere, actually.
Hmmm...
>> ...the other varies the time
>> constant of an RC
>> circuit formed by C13/VR4/R46 so that as the resonance is
>> increased, the
>> attack is lagged by C13 giving the distinctive 303
>> "weoow". It's damn
>> near impossible to emulate on other synths ;-) In fact,
>> only 303 clones
>> and one 303 softsynth get it nearly right...
>
> Ah.. I seee. I hadn't analysed the sound in such detail, I must admit.
And I don't have a 303 of my own to run tests on, sadly..
> So is the filter env attack only altered on accented notes, or on all
notes, as the resonance is increased?
No, it's only on accented notes.
If you have a look at the circuit for the 303, you'll see that the gate
pulse is differentiated by C54/R148 and buffered by Q36 etc. so it can
charge C62 via D37/R152. The decay control discharges C62 through
D26-D28 and R138, with the first having a resistor to bias it to around
0.6v, presumably to stop it doing odd things to Q39 (I don't fully
understand this bit but suspect it gives the envelope the correct
exponential curve).
Now when accent is triggered, one of IC12's analogue switches shorts out
the decay pot, leaving only R138 to set the decay time. Another of
IC12's switches sends the envelope pulse to one end of the accent pot,
with the wiper going to D24 in the filter accent circuit and also to the
VCA, where it gets added to the the "normal" VCA envelope.
Note that because of D24, the resonance control doesn't affect the VCA
envelope rise time.
I'm afraid I'm not very well-up on microelectronics, sadly.
I probably should be, given the amount of time I've spent fiddling around with various kits over the years...
Damn. I've just spotted a bug in my plugin model ;-)
Glad to be or service (if unknowingly).
a|x
Gordon
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