What is the term for this type of "effect"?

[pappasmurfsharem]

For reference think of the intro to Tom Sawyer by Rush.

I don't know if it is an Oscillator or Filter effect or neither. When you hit the first note on the synth and the note goes from a slightly higher pitch and decays to a lower pitch.

I'm asking because I would like to know how to add this effect to a pedal.

I'm thinking about using the Synthbox as a starting point and adding the above to create a guitar synth pedal.
Perhaps with some help on adding an attack and decay knobs to create a moog style synth pedal

Any other pedals too look at with something similar.

[artifus]

i'm not clear on what you are asking, could you clarify please? do you mean the filtered synth sound in the first ten seconds of this:http://www.youtube.com/watch?v=U7DFsBcVMDA? (a link would save others searching on your behalf). you would like each picked note or strummed chord to behave in a similar manner? felines may be parted from their exteriors in many ways... envelope filter and cmos is my first thought, but as i say, i'm not clear on what it is you are asking for exactly.*

*not that i'd have an answer, anyway...

[pappasmurfsharem]

i'm not clear on what you are asking, could you clarify please? do you mean the filtered synth sound in the first ten seconds of this:http://www.youtube.com/watch?v=U7DFsBcVMDA? (a link would save others searching on your behalf). you would like each picked note or strummed chord to behave in a similar manner? felines may be parted from their exteriors in many ways... envelope filter and cmos is my first thought, but as i say, i'm not clear on what it is you are asking for exactly.

Yes, like I said the decay of the synth from the slightly higher tone to a lower tone. I'd be looking to add this on the the synthbox I posted above. Preferably with an adjustable rate. maybe even attack, and decay.

[tubelectron]

Well,

If it is about the guitar, I would try a Ge fuzz placed before a phase 90 or a Small Stone...

A+!

[Mike Burgundy]

I think the sound you're referring to is a swept bandpass over a harmonically rich synthchord. The harmonics mean the sweep actually has something to sweep through, giving the impression of decreasing pitch but the chord is actually held.
That is firmly in synth territory - but no one ever made a rule you can't use a guitar as the signal source.
This stuff can get real complex real fast (think of a moog modular.....) but basically you want a Voltage Controlled Filter (bandpass) and some way of triggering it downwards. Instead of an LFO sweeping the filter up and down, you want it to trigger at the start of audio input, make the sweep down, and stop. End of audio = reset filter to the top.
I don't have anything ready cooked, have a look at the numerous DIY synth sites for ideas, maybe?

[artifus]

so i think you want an envelope controlled filter, but do you want that to effect your guitars direct output or a guitar derived 'synth' sound. fuzz through a filter will get you close if that's what you want.

basically, you want to research filters and envelope detectors. i think. i'm still not 100% but that prolly says far more about me than it does you.

[pappasmurfsharem]

I think the sound you're referring to is a swept bandpass over a harmonically rich synthchord. The harmonics mean the sweep actually has something to sweep through, giving the impression of decreasing pitch but the chord is actually held.
That is firmly in synth territory - but no one ever made a rule you can't use a guitar as the signal source.
This stuff can get real complex real fast (think of a moog modular.....) but basically you want a Voltage Controlled Filter (bandpass) and some way of triggering it downwards. Instead of an LFO sweeping the filter up and down, you want it to trigger at the start of audio input, make the sweep down, and stop. End of audio = reset filter to the top.
I don't have anything ready cooked, have a look at the numerous DIY synth sites for ideas, maybe?

Sounds like you are right on the money. Here is the synthbox audio clip. Which I believe is being run from a guitar http://www.aronnelson.com/gallery/main.php/v/liquids/Synthbox+2+Demo.mp3.html.

That would be the base if what I want with the bandpass you speak of after it

[pjwhite]

Tom Sawyer opens with a portamento sweep on an Oberheim OB-X or OB-Xa with all eight voices playing in unison.  That's where the pitch glides from the starting note (high in this case) to the ending note (low). 

[haveyouseenhim]

I was able to get a VERY similar sound by running an atari punk console through a few pedals. I think I used a delay and a digitech digiverb. Just experiment with different effects.

[pappasmurfsharem]

Tom Sawyer opens with a portamento sweep on an Oberheim OB-X or OB-Xa with all eight voices playing in unison.  That's where the pitch glides from the starting note (high in this case) to the ending note (low). 

Exactly but how do I replicate that portamento with a circuit

I was able to get a VERY similar sound by running an atari punk console through a few pedals. I think I used a delay and a digitech digiverb. Just experiment with different effects.

That's not really what I want though. I have a Line 6 Variax Bass that nails the sound perfectly by itself without any pedals, however I'm just using that as a reference for the filter effects I would want to add to the synthbox pedal I posted above

[aron]

> Exactly but how do I replicate that portamento with a circuit

The closest would be whammy pedal. Portamento is a continuous glide between notes.

[pappasmurfsharem]

> Exactly but how do I replicate that portamento with a circuit

The closest would be whammy pedal. Portamento is a continuous glide between notes.

Ahh well then that isn't the term for the filter effect I'm thinking of then.

I believe Mike was on the right track

I'm lookg around on MFOS is there is anything that would do what I want, and I'm sure there is, but I'm not sure what the technical name of a frequency sweep without oscillation is called

[GGBB]

I'm in way over my head here, but the first guitar thing that comes to mind is an auto-wah with fast attack and slow decay and a higher (and wider?) frequency range.  Or a wah pedal with the same frequency adjustments if you want to sweep manually with your foot.

[Quackzed]

 a foot pedal controller isnt a bad idea...simple, control a  bandpass with a footcontrolled pot.
if you plan on using it after a synthbox,  where the signals volume envelope will be a pretty steady volume from attack to decay, using an envelope filter will have no sweep...
or what about a clean sidechain in parallel to the synthbox that feeds the envelope filter (modded for bandpass, maybee steep and narrow...?!?) and let the
envelope filter action affect the output of the synthbox...
iirc the schocktave had a clean blend that you could borrow to feed an envelope filter, and get the filter end to affect the synthbox side...not sure but it could probably be done easily, i just dont know envelope filters that well  ...
that would be cool tho... xtra synthy.

[Kesh]

Tom Sawyer starts with a filter with resonance turned up, sweeping down over a keyboard note. The filter is so resonant that it is on the point of self oscillation so adding its own note as well as modifying the original note.

If you want it in a pedal, you will either have to trigger the sweep some way, or control it with a foot pedal. Your could trigger it with the amplitude of the input, and you will get some pretty odd effects if you play anything more than a slow one not line.

[aron]

Hmmm apparently done on an Oberheim OB-X. 2 pole filter - with X-mod - meaning the oscillator is also modulation the filter (forgot about that switch). Since the Oberheim 2 pole filters didn't self-oscillate, you can turn up the resonance all the way or close to it.

http://www.rainycitynights.com/band/rush_stuff/tomsawyergrowl.htm