Electronics Clarification Question

[rogertvr]

Can someone explain something about Signature Electronics for me please?
 
I know that the Q switch adds 8db (?) to the attack of the note. Do the filters work like the cutoff frequency on a synthesizer? i.e. it's what I would know as 'subtractive synthesis'. The filters add neither cut or boost to the output signal, but instead alter the point at which frequencies generated by the pick-ups are blocked from being output?
 
Thanks,
 
Roger

[adriaan]

Roger,  
 
Here's the Electronis 101 thread on filters:
http://alembic.com/club/messages/393/7213.html
 
I have little knowledge of electronics, but many years ago spent a lot of time fiddling with the pots, sliders and cables of an Arp 2600 - so I have a vague idea of what you mean by substractive synthesis. The memories are dim, but let's see what I can come up with.  
 
A quick Google search tells me it was a version 3 model (http://www.vintagesynth.org/arp/arp.shtml) which had a problem with the filters, which made it sound dull. Actually they had to make a change because of a Moog patent, so that's an excuse, I guess.  
 
Another site has the owner's manual (http://oldschoolsound2.free.fr/manuels/arp2600%20owner%20manual.pdf) and on page 18 there's a description of the principles of a low pass filter.  
 
The classic Alembic on-board filter is a low pass filter, so you have a pot to adjust the starting point for cutting off the highs (a.k.a. the cut-off frequency). The laws of electronics dictate that there is a 'natural' boost around the cut-off frequency. The Q switch further increases this boost, but only around the cut-off frequency.  
 
So it's not a boost in the Attack part of the ADSR envelope (any acoustic signal can be broken down into Attack-Decay-Sustain-Release, for which old synths like the Arp 2600 had corresponding pots; touch-responsive keyboards came around only in the 1980s, with a hefty price tag) but rather a boost in the frequency spectrum. It does sound as if you've turned up the volume, but that's probably a psycho-acoustic phenomenon.  
 
Adriaan
 
(Message edited by Adriaan on February 15, 2004)

[rogertvr]

Thanks Adriaan for your reply.
 
I'm a lot wiser now - I've had a read through my synthesizer manuals. I've been trying to relate the controls on Alembics to normal electronics on basses I own or have owned - of course that's not possible. However, if I relate to various type of pass filters, cut off frequency and the resonance control on my synthesizers, I fully understand how Alembic electronics work. Well I do until the Dragon's Wing arrives and I suddenly realise I have it all wrong!!!!!!!!
 
Cheers,
 
Roger