Stereo Pan Tremolo

[AzzR]

How do you mod a tremolo for stereo pan? Can it be done on the Pulsar.

Also im looking for articles on the EA tremolo, Which is the best place to look?

-Dream

[R.G.]

There are three ways.
(a) have a modulator that already provides pushme-pullyou outputs, like some multiplier cells.
(b) subtract the tremolo-ed signal from the input signal. When the tremolo-ed signal is at max, it cancells the dry signal and makes for an opposite output.
(c) add a second modulator and generate an inverted control signal

The pulsar is actually a good place to do (c). The modulator is just an opamp and an NPN transistor, so it's cheap to double up. (b) is always possible with one or two more opamps on any tremolo, but achieving perfect balance can be chancy.

[Mark Hammer]

Stereo pan tremolos involves a few basic things.  First, you have to have an LFO.  Second, you have to have something whose gain or level can be controlled by the LFO, AND you have to have two of them.  Third you have to have a means of producing different versions of the control signal from the LFO.  The most common is to simply invert the LFO going to one of the control elements, so that when one side is going high, the control element for the other channel is going low. 

A somewhat less common version, however, might include what is called a "quadrature oscillator", where the two LFO outputs are not 180 degrees out of phase (i.e., completely opposite in nature), but rather only 90 degrees out.  Here, when output A has reach rock bottom (no output level at all), output B is halfway down going in that direction.  And whan output A has reached peak output level (or is halfway, going to full level), output B is just trailing behind it.

A third, less common way than that is to simply use a two independent LFOs driving two gain cells, and feed the instrument into a splitter.  This has advantages and disadvantages.  The disadvantage is that it involves more parts and more tweaking.  Since the two LFOs are not synced to each other either, you can't simply make the whole thing go faster or slower with one knob; although I suppose you might with a dual-ganged pot.  The advantage is that you get unexpected and surprising patterns of movement and a more animated sound. 

Generally, the human ear prefers this to the fixed cyclical sweep of up and down and up and down and up....  My sense, though, is that if you want very pronounced tremolo, periodic/cyclical tremolo from a single LFO is the way to go since the "surprises" of dual LFOs can be a bit jarring.  On  the other hand, if one wants to use lightmodulation, the semi-randomness of dual LFOs can add a pleasing twinkly dimension and more animation, like butterfly movements. 

The linking principle is that of striking the right balance between surprise and predictability.  When things become too predictable, we lose interest.  When things become too UNpredictable and incoherent, we also lose interest.  So, with heavy modulation, single-LFO modulation allows us to follow the music despite the on/off thing being superimposed.  If the on/off thing started to become random, it would be too hard to track the music.  If the modulation is much less than hard on/off, and the music is easy to follow mentally, despite the modulation, some randomness will start to make it intersting to the ear again.

I guess a reasonable analogy might be this.  Take a realistic photo image with lots of identifiable features.  Now cut it up into square jigsaw pieces and spread the pieces of the image out a bit so there are gaps between the segments. (but not shuffling the pieces around)  You can probably still identify and even appreciate what is in the original photo image.  heck, you may even find you LIKE the effect.  Okay now take an impressionistic painting and do the same.  Chances are, you will not be able to recognize the original painting or appreciate its hedonic quality (i.e., its degree of pleasantness/unpleasantness).  Why?  There are limits to how much randomness and fragmentation of patterns we can tolerate.  The impressionist painting already has some randomness embedded into it, and adding more just makes it that much harder for the images in the painting to easily emerge for the viewer.  The human mind likes a bit of work when perceiving, but starts to choke when the work involved exceeds some level.

The "ideal" general purpose stereo tremolo, then, would have the capacity to sync two outputs to either a single classic opposite phase LFO, a phase-lagging quadrature LFO, or dual LFOs, depending on the effect desired, speed range aimed for, and amount of level modulation (i.e., tremolo depth) used.  of course, you'd never fit that into a 1590B.  Well, maybe Zach could, but not a mere mortal.

[AzzR]

WOW! Thats one hell of an explanation, Thanks.

What im trying to archieve if Ive understood properly is two tremolos in one circuit each one 180 degrees out of phase, I want to have one slowly panning and one quickly panning, Essentially I want two stereo pan tremolos in one but I want them set up in a way that I can also use them both seperatly. I would also like them to be able to also work on a mono channel (if its possible) so that instead of stereo pan it works just like a normal tremolo.

Is it wise to use two different tremolo circuits in the one unit?

I would rather try and have it all in one box rather than use a splitter.

Sorry if this dosent really make sense, My explanations are fairly crap.

Thanks

-Dream

[A.S.P.]

Can it be done on the Pulsar.

Yes, on the so-called E-H "re-issue" Pulsar, it can be done... 

[A.S.P.]

...two tremolos in one circuit each one 180 degrees out of phase, I want to have one slowly panning and one quickly panning, Essentially I want two stereo pan tremolos in one

that would be the "Bi-Pulsar"...
(a so-called :Bi-Trem)

[blanik]

Yes, on the so-called E-H "re-issue" Pulsar, it can be done... 
[/quote]

Do you mean it's not like the original circuit? (talking about the Tonepad Pulsar)

R.

[TELEFUNKON]

that would call for a 4PDT stompswitch, wouldn`t it?

[AzzR]

No idea. These are the kind of things I am trying to figure out

[AzzR]

If anyone listens to Cradle Of Filth, listen to the song Nymphetamine (Fix) at about 2:40 you will hear the effect I am trying to archieve.

*EDIT* or download it here http://www.haggardfx.com/downloads/Stereo_Pan_Sound.mp3

-Dream

[A.S.P.]

anybody mentioned fourpoledoublethrowswitches??? 

[Processaurus]

Go 3pdt w/ Milenium for true bypass, I've heard reliability is poor with the currently available 4pdt's.  Or buffer the input.  That would actually be better if it goes directly to two amps.