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Vbm question?
MUFF WIGGLER Forum Index -> Video Synthesis  
Author Vbm question?
Matos
Since you all love my deep, and earth shattering questions..riddle me this.
On the vbm if nothing is inserted into a input, let's say 2c, then it acts as a 1v bias. Now, as far as I can gather, bias is Just a constant value to the signal. Now, I wanted to control the amount of bias via cv. How would you go about this task? It seemed mentally easy, but my understanding of how video works is highly colored by my audio experience, which I'm quickly learning have little to do with each other except for blinking lights and twisting knobs. An I just dense? Every time I feel as if I'm begging to grasp the larger picture, my mental sync fails to be gen locked and everything becomes fuzzy. hmmm.....
daverj
A DC bias gives you a fixed shade of gray in video. Run that through a VCA and you get a voltage controlled shade of gray.
lizlarsen
It all just comes down to voltages and arithmetic in the end. A DC bias of 0.5V in an LZX patch is 50% gray, like Dave says. Typically you don't need to voltage control anything about that... just use the CV signal itself as the source signal instead of the bias.

Here are some random Notes & Facts!

Summing a DC bias with your signal is adjusting brightness
Adjusting the gain/attenuation of your signal is adjusting contrast
Summing two unipolar (1V, LZX standard signals) is brightness based mixing (you are adding or subtracting from brightness)
Summing two bipolar signals (+/-0.5V) is contrast based mixing (the signals subtract or add from each other's contrast -- LZX modules don't output bipolar signals natively, but you can make them bipolar with TVP, one of the many utility purposes it's useful for)

A big thing here is try to sum signals of all kinds of frequency ranges with each other (video, lfo, audio, etc.) A lot of time adding voltage control to something is as simple as summing it with an LFO (a big thing TVP is designed for.)
Matos
Hmmm...I think I sorta, kinda understand. Essentially, I was using the vector patch as shown on the lzx wiki. Adjusting 1c and 2c controls the dry wet of the brightness position in the patch. I wanted to cv control these knobs to shift the brightness position effect. While turning the knob does this wonderfully, any cv that I feed in simply shifts the position either on the y or x axis based in relation to where I patch it in. Not in the sext rutt way, but in the interesting, but not quite what I need way of up or down, purely in the animation realm. I've tried a variety of methods, but so far I've been unable to achieve this. I kinda gave up and decided to unplug everything to try and organize the hellish monstrosity of power cables that are feeding this video rig. Any tips on how to achieve the above?
smrl
do you have the triple video fader / key generator? if I understand you correctly, you could accomplish this with one of those. You'd put the signal into the A or B side of a channel in 'fade' mode, put the CV into the CV in, and then you'd get control over initial value and control voltage influence. Right now you're not scaling those signals, you're just biasing them up or down with the CV.
Matos
No.not yet....I hope to grab one in two weeks. But that makes sense. Well, there's still plenty to explore. Getting some beautiful stuff, but I want to squeeze everything I can out of this rig.
smrl
Here's an audio modular analogy:

Imagine you've got an LFO you're using as a modulator of something. You want to scale the modulation depth of the LFO over time, and you want to do it with a control voltage.

So you take the CV and you feed it into a DC mixer along with the LFO. Now at the output, you'll notice the LFO is not changing magnitude when you add/subtract DC - you're just biasing it up or down with that voltage. This is what you've accomplished adding CVs to the VBM.

Instead, what you'd want to do is take the LFO and run it into a VCA, and have your CV control the VCA. Now you get a signal which increases/decreases in magnitude with a higher/lower DC voltage. This is essentially what the TVFKG does in fade mode with nothing plugged into one of the two channels.
Matos
Thanks smrl! I totally get that analogy. I was on a similar path, feeding the lfo into the vca, having silent way sequence the vca, but I was just feeding it into the vbm. I've only had it for a few days, so I'm still in the plug anything into every hole and see what happens mode. w00t But since I'm mixing tons of euro and lzx, sometimes I'm not sure if I'm scaling the signals properly, or if I'm just misunderstanding a signals flow. seriously, i just don't get it Thanks for the clarity.
lizlarsen
Yes, for what you describe, you want to use a VCA! To relate it back to my notes & facts above, you're wanting to voltage control the gain of the signal.

Voltage control over contrast = run the signal thru a VCA
Voltage control over brightness = sum a DC offset with the signal

TVFKG is meant to be the swiss army nice of the set of basic modules. It is currently the system's only VCA module. Eventually we may release a more compact multi-vca or matrix-vca type thing, but right now TVFKG does the job. In a vector patch, I love using it to crossfade between ramps or various ramp mixes and inversions that are feeding the VBM matrix!

Scroll down to the bottom of this page... have you seen the interactive flash animation at the bottom? Play with that, it might help understand the VBM's modes a little better:
http://www.lzxindustries.net/interface
johnnywoods
Also, remember that most audio VCAs will cleanly process Ramps, so you can save some Keyer channels. if I recall correctly, when Lars and I did our Scanimate style experiments, we were running a bunch of ramps into a VCAMatrix to get some of the effects.
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