Friday, March 6, 2009

CV Monitor Tool

In the course of developing my Noise Gate, I found it very useful to visualise CV signals in real time. In fact, it surprises me that there isn't a built-in way to do this. So I thought I'd share my very simple "CV Monitor" combinator.

Figure 1 - The CV Monitor

Figure 2 - Connect CV signals to indicated ports

It's a very straightforward device to use - simply connect any CV signal you're interested in to one of the ports on the back of the Combi, as figure 3 demonstrates with the SubTractor's LFO output.

Figure 3 - SubTractor LFO connected to Pitch Bend CV input

Turn the rack around and you'll see one or more of the DDL digital displays changing in real time according to the incoming CV signal. Because the DDL delay starts at one, not zero, I have centred the displays at 1000. So just ignore the leading 1 and read the CV value directly.

Note that the rotary and modulator monitors are restricted to unipolar CV signals from 0 to 127. If you want to view a bipolar signal (such as the sinewave from the Malström LFOs) then you'll want to connect this to the Pitch Bend input. This will display the CV signal from 1 to 2000 for full-range deflection of the Pitch Bend wheel.

This hints at something to be aware of. Reason seems to do CV scaling where necessary, so thinking in terms of absolute CV values can be dangerous at times. For example, if you connect the SubTractor triangle-wave LFO to the Pitch Bend input, you'll see full deflection of the Pitch Bend and therefore the DDL will display a signal oscillating between 1 to 2000. But if you connect the same signal to, say, Rotary 1, then two things happen:
  1. the signal is truncated for negative values, so the DDL will show 1000 for those parts of the LFO waveform.
  2. the signal is scaled so that the maximum CV value maps to the full range of the control being modulated, in this case 127.
So what is the actual CV value? Does it actually matter? It looks like the effect of the CV signal depends on what you connect it to. This is actually quite useful because it means if the CV generator is oscillating full-range, then whatever you connect it to will also oscillate full range, regardless of the resolution of this destination. Therefore I suppose it might make more sense to think of CV signals as percentages, where unipolar full-range is 0 to 100%, and bipolar full-range is -100% to 100%.

I'll think about this some more - if this is true then it might make far more sense for the rotaries to map from 1000 to 1100 instead.

Also note that the Pitch Bend wheel generates CV values from -8192 to 8191, a range that exceeds the display capability of the DDL delay. The Combi programming scales this range down to 1-2000 for display.

The Combi also accepts and displays Aftertouch and Expression MIDI signals, in case that's useful.

Here is the Combinator Patch.

RNS Example 1 has a bunch of CV automations driving the Combi controls directly. Hit 'play' to view.

RNS Example 2 has several LFOs being monitored simulataneously by the device. Note that the SubTractor LFOs are all bipolar, so you'll see the display stick at 1000 for those parts of the waveform that are below half-way.

I hope you find this useful at some stage.

1 comment:

  1. Haha... Yeah, I came across with this one aswell when I used a combi and connected the LFO to the 2 Parameter EQ. I went like "wtf... it is alive!".

    What is interesting with this is using a Cv merger and use the normal split and the inverted split (last slots are inverted).

    Also merging can result into 'strange' behaviour (since merging also has an amount connected to it).

    But with the delays it just becomes 'visual' eye candy so you know what you are doing!

    Great post!