CV control, Expression input, LFO and a bunch of other electronic stuff I don't get!

[Kwesi]

So I've been thinking about it for a while and talking to some people but after seeing the video that John Davis posted (http://vimeo.com/10048959) I really want to get into the whole "live electronica" thing starting with my pedalboard. But before that I think I should know exactly what I'm getting into and at least some of the mechanics behind it. The only thing I know right now is that it's expensive lol but what cool gadgets and such aren't? I'm probably going to be making other threads centered around slightly different topics but I wanted to post this one while I still had it in my mind.

So exactly what is CV control? What does it mean? What does it do? How do you use it? And how is it different from control via expression pedal?

And because I feel like this is related, what exactly is an LFO what are it's applications. The most I know about it is the "Wah-O" sound it can create. Video and audio clips would be greatly appreciated if at all possible. I get things better when I can see them work.

[Taylor Livingston]

CV=control voltage. Allows you to control parameters by sending a varying voltage into a piece of gear. Many effects do this internally, generating a control voltage like an LFO, and then using that to control some sound parameter, like filter cutoff frequency for example. Some more complex gear is able to send and receive control voltages between devices, like Moogerfoogers, Lovetone, and most notably modular synth gear. An expression pedal sometimes IS a CV pedal.

LFO=low frequency oscillator. You can think of this as just like somebody turning a knob on your pedal up and down, over and over. For example, a tremolo pedal is an LFO controlling volume, so it's just like if you had a guy turning the volume knob on your bass up and down over and over. By itself, an LFO doesn't make any sound (well, sometimes it makes a ticking sound in poorly made effects ) - you need it to control something in order for you to hear it. Many other common effects are just an LFO controlling one parameter. Flanger, vibrato, and chorus are all variations on a delay with its time controlled by an LFO. A phaser is (unsurprisingly) an LFO controlling phase shift. The LFO gives all these effects the wavering, rotating, animated sound for which they're known.

So what's it all for? A major aspect of electronic music is the way that the sound changes all the time. Whereas in a rock song, the sound of each instrument might change in one abrupt moment (stepping on a distortion pedal when going from verse to chorus), electronic music often involves animating the sound quality of one or more instruments to a complex degree. Control voltages allow you to not just "turn a knob up and down", but turn it slowly and then fast, virtually control a knob with how hard you hit the strings, etc. which allows you to make a bass sound that's constantly changing.

[stranded horse]

Does one have to get one those expensive moogerfooger to get a decent low pass filter by the way?

[fightthepower]

Originally Posted by stranded horse

Does one have to get one those expensive moogerfooger to get a decent low pass filter by the way?

You can find the 'fooger lowpass filter for about $200 used, and it is the lowest priced pedal for this application imo. If you can live with a rack unit, the Electrix filters are definitely worth checking out as they are a few bucks cheaper than the Moog pedal. Potentially even better would be conical jonhsons new filter (the guy who posted above) which iirc will be a simple lowpass filter that should be good for the 'live electronic' or 'synthy' application(ota filter I imagine?); I don't know how it will be priced, but I imagine it will be reasonable and in a package much more convenient than the Moogerfooger.

[Mr. Pickles]

Kwesi,
I would suggest that you watch some of the videos on the Moog site to see some examples of CV and LFOs in action, as Moog is one of the pioneers of modular synthesis. Start with the LPF and other Moogerfooger vids.

[bongomania]

Also, there is almost no better education for this than working with a modular synthesizer. Obviously not everyone has access to a rack of Buchla or Serge modules, but there are lots of software emulations of these things, and they are great for learning how it all works.

[Kwesi]

Thanks for the answers guys and I'll be sure to check out the moog vids on youtube Mr. Pickles.

As far as CV controllers vs. Expression pedals. When are they different? Let me try to give an example or two here. How would plugging a Moog MP201 into an MF101 or a Robot Facotry Brain Freeze differ from using an expression pedal if at all?

On a related note are the cables used to connect CV controllers and expression pedals to the CV/expression input on a pedal different than regular instrument cables and if so where can I get them? And on a not so related note, what are all the jacks on the MF101 for? Just curious.

[bongomania]

CV/expression pedals can operate a few different ways:

Some are just passive pots, AKA variable resistors. The effect box sends a voltage signal out to the expression pedal, the pedal attenuates that voltage by some amount, and the signal then passes back into the effect box. That attenuated voltage controls the "amount" of some parameter.

Some contain their own voltage generator, and the treadle controls the amount of voltage sent out to the effect. Same basic idea as the passive one, except if you use a passive expression pedal with an effect box that doesn't send its own voltage out through the CV connection, then nothing will happen.

With passive ones, the effect may need a specific resistive range to work properly. Some have a built-in trim pot to adjust that range, but not all do. With active ones, the effect will need to receive a specific range of voltage at its input; wrong voltage = wrong response to the control. Some active expression pedals will have a trim pot to adjust the max range of voltage, but again you can't assume it.

Most expression pedals use a TRS-TRS (stereo 1/4") cable, whether active or passive.

[bongomania]

Moog in/outputs:
audio in = plug bass in here
cutoff = frequency corner of filter
mix = controls the blend of dry and filtered signals
res = resonance = the intensity of the "feedback" ringing/wet quality of the filter.
amount = range of the filter sweep
audio out = goes to amp
env out = sends the dynamically-controlled envelope shape to any external effect, so you can control other modular synth type pedals with the same envelope as that filter is using.

[Gashaponcito]

Originally Posted by bongomania

but there are lots of software emulations of these things, and they are great for learning how it all works.

could you be a little more specific please?

[bongomania]

Well, not really, because I am a fanatical hardware kinda guy. But I have seen literally dozens of different modular synth software packages out there, either stand-alone or as plugins for Protools or other popular platforms--so they will not be hard to find at all, if you look.

[Taylor Livingston]

A good list:

http://en.wikipedia.org/wiki/Modular...e_music_studio

[Mr. Pickles]

I'm in the same boat as the OP.

Synthesizers fascinate me, but my experience is limited to software. Waiting for my copy of Modular Synthesis for Dummies to shed some light on the subject.

[Kwesi]

Thanks again for the info Bongo. Unfortunately, it didn't quite answer my question .

Originally Posted by Kwesi

As far as CV controllers vs. Expression pedals. When are they different? Let me try to give an example or two here. How would plugging a Moog MP201 into an MF101 or a Robot Factory Brain Freeze differ from using an expression pedal if at all?

I guess the best answer I could ask for would be soundclips but I don't know how viable an option that would be for anyone here. I guess what asking is when are they controlling different things or is that on a very case by case basis? And for those of you who have used an MP201 and an expression pedal with a wah brain or lowpass filter how did they work differently?

[bongomania]

As to "when they are controlling different things", that depends on (a) any hardwired control voltage routing, and (b) any optional CV inputs or switchable routing.

The idea is that increasing or decreasing a voltage, routed into the control over one parameter, will change that parameter. A parameter may be damn near anything: amplitude, frequency, filter peak, resonance, blending, really anything that could conceivably be controlled by a rotary knob or a multi-position switch.

How it specifically works will vary totally between different devices.

Imagine any one knob on any effect pedal--or even any one knob on your bass! Then imagine there is an invisible hand turning that one knob. That's like CV. It has nothing to do with any specific function, only what you (or the pedal designer, usually) have routed it to do.

[Kwesi]

Lol, I don't know why I thought it could actually be simpler than that. The knob analogy pretty much set it straight for me. I guess I'll have to try it out for myself .

[Taylor Livingston]

Maybe to be a little more specific to our question, the difference between an expression pedal and an MP201 is that the expression pedal just allows you to "turn a knob" with your foot. So you can only turn that knob in the ways that your foot can physically move. There is a limit to the speed and precision that most folks can operate their feet.

Whereas with the MP201, you can set it to do all kinds of more complex knob turning. So at its most basic, it's still just turning a knob to change the sound in a particular way. But the MP201 can turn that knob up and down at hyperspeed, and with more precision than your foot can.

[fredguy]

I'll throw my $0.02 into the mix. I'm a long time bass player, with an absurd gear to ability ratio, and have recently stuck my head into the world of modular synths. The above explanations of cv and lfo are spot on but what the use of lfo control of cv's allows is to change the waveform of the lfo. At one extreme you could have a square wave lfo controlling a cv. If this was sent to an amplifier it would act like a switch turning your volume on and off. A triangle or sine wave would provide a tremolo sound ramping your volume up and down. A sawtooth lfo would ramp your volume up and the abruptly drop it back down. These waves could also control a filters cutoff frequency, phase, or an effects wet/dry mix. Now imagine you can control the frequency of that lfo with another lfo. The possibilities are endless.

If you want an thorough read on synthesis have a look at the synth secrets series on the sound on sound web site:

http://www.soundonsound.com/sos/allsynthsecrets.htm

Start at part one and go from there. I'm also happy to try and answer any specific questions.

dave

[Eric!]

I'm glad you asked about CV, I was wondering the other day, and now I know!

[fightthepower]

Originally Posted by Kwesi

Thanks again for the info Bongo. Unfortunately, it didn't quite answer my question .



I guess the best answer I could ask for would be soundclips but I don't know how viable an option that would be for anyone here. I guess what asking is when are they controlling different things or is that on a very case by case basis? And for those of you who have used an MP201 and an expression pedal with a wah brain or lowpass filter how did they work differently?

The MP201 is basically the brain behind all the single function specialty and novelty effects on the market. Pair it with a few pedals that have CV inputs (many exp inputs also work well, like EHX pedals), and you can replace a large board single function pedals... with a large board of a few big ass pedals But you get a lot more control, you get to design your single function effects into presets instead of stompboxes. We'll focus on a simple filter: we have boxes for filter driven by dynamic 'envelopes', filters called 'autowahs' generally controlled by simple sine or triangle lfo's, filters housed in treadles called 'wahwahs', sample&hold and stepped filters which are also just lfo-driven filters, etc. Notice these are all just filters with a different type of modulation, either a control voltage from the strength of your attack, or a control voltage that moves the filter around based on the knob settings only.

With an MP201 and a Lowpass filter, you can create all of those filter effects and have presets for each one. Here are a few examples of what you can do with the MP201 in a bass guitar setup-- there's a whole other world if you're using a computer in your setup, or if you add a CP251, and chain up a few 'foogers and use it as a monosynth with a MIDI keyboard! The MP201's MIDI/CV converter works very well.






__________________________________________________ __________
With the MP201, you can use it in 'expression' mode, and basically it acts as a big sturdy expression pedal with an extra smooth sweep; by using it as an expression controller, it is basically patched into the 'wah brain' and becomes the treadle; a modular cry-baby you could say.

Now, we're still using the MP201 patched into the 'wah brain' or 'lowpass filter''s "frequency" input: Go into the MP201's menu, change it from "expression" mode to "LFO" mode, and select an LFO; pick, for instance, a 'triangle' lfo. This LFO will now be automatically sweeping the filter, and we have now turned the 'filter/wah brain' into an "Autowah", or potentially a "dubstep wobble"*

*Since we're not using the MP201's treadle to manually sweep the filter anymore, we can set it to control other things, like the rate of the LFO, the amount of LFO sweeping the filter (ie small sweep or wide sweep), etc. You can also tap in the tempo of the modulation with the adjacent footswitch, or set it to follow a MIDI clock. The MP201 gives you tap tempo functionality to all pedals that have inputs, be it phaser, flanger, filter, etc.

With the MP201's 100 presets, there is plenty of room for presets for all types of sounds. If you have the MP201 plugged into the Lowpass filters Freq, Envelope, and Resonance inputs for instance, you could quickly switch from a synthy lowpass sweep with high resonance, to a wet & bubbly envelope filter, to a dubbed out lowpass filter with no resonance for huge low end, , to a sample&hold filter or self oscillating r2d2 speak, in seconds.

With the Ringmod, you can patch the MP201 into the "carrier in" and use it as a:
*volume pedal, in expression mode
*tap tremolo with lfo's
*treadle or footswitch activated slow gear with the HADSR envelopes
*VCA in a modular synth setup.

With the Moog Delay, you can use the MP201's 'expression' mode patched into the 'Delay Time' input, and with a little bit of work with a stopwatch, you can make presets for certain BPM's that you play in, and use the treadle to control the delay time for slight adjustments in tempo; you can also limit the range of the exp pedals, giving you linear adjustment of a small range throughout its full sweep, ideal for small changes. If you patch a triangle LFO into the delay time input, you can use it for chorus and/or vibrato.



Anyway, I have to stop somewhere, but hopefully that will give you a clearer picture of the MP201, Control voltages in the forms of envelopes/LFO/expression, and how they're applied to regular effects like a plain filter to create the 'step filters' and 'tremolos' and etc. Also, fredguy who posted just above me is also right on the money, a lot can be learned from those soundonsound articles.