Tuesday, March 24, 2009

Dual Edge CV Gate

Allow me to introduce a rather unusual device. I'm not sure if a proper name exists for this, but I have decided to call it a "Dual Edge CV Gate".


RNS File

Actually it's not really a gate - it's more like a switch. The device is designed to switch on or off depending on the input CV signal. When the switch is on, it will output a high CV signal (127); when off it will output a low CV signal (0) . There are two thresholds - lower and upper, such that if the input signal is between these thresholds, then the switch is on. If it is below the lower threshold, or above the upper threshold, then the switch is off. Figure 2 illustrates this relationship.

Figure 2

It would be fairly straightforward to extend this switch to control a gate which passes or inhibits the original input CV signal. This way you would get a 'piece' of the input CV signal for a particular domain, instead of a straight on/off value.

So how does it work?

Figure 3

Well, once again the Thor synthesiser is more than just an audio synth. Inside a Combinator and with some careful routing rules, Thor is able to implement two step functions. One of these step functions is flipped over. When combined with a logical "AND" operation, the result is a pulse, as illustrated by figure 3.

Figure 4

Figure 5

Figure 4 shows a simplified view of the cabling connections on the rear of the device and figure 5 shows the Thor configuration. The input CV signal is connected to the "CV Input" Spider CV Merger, which drives the Combi's Modulation Wheel input and in turn the Thor modulator wheel. Routing rules 1 to 4 combine this value (sum) with DC signals (via CV In1). However these DC values are scaled by the two Thor Rotaries, labelled "Lower Trigger" and "Upper Trigger". Combi knobs 1 & 2 adjust these rotaries, thereby allowing the user to adjust the DC level added to the Mod Wheel value. The output from these rules (CV Out1 & Out2) are connected to the Combi knobs 3 & 4. These are programmed to modulate the Thor Main Buttons. In a similar manner to my Noise Gate, these buttons only activate when the controlling knob reaches it's maximum value (127). Knob 3 activates Button 1 when the sum reaches 127, and knob 4 activates Button 2 when it reaches 0.

This provides two configurable thresholds - upper and lower. The difference between them is that one will activate when the input signal is above the lower threshold, the other activates when the signal is below the upper threshold. You can see the Thor Button1 & Button2 lights activate when the respective thresholds are crossed. You can adjust the thresholds by setting Combi knobs 1 & 2. Typically, you would set knob 1 to be less than knob 2, otherwise the gate will never open.

The long routing rule (CV In1 > CV Out3 / Button1 / Button2) implements an "AND" operation. CV In1 is a DC signal (value 127). This value is passed to CV Out3 when both buttons are on. If either or both are off, CV Out3 is driven to zero.

There's a bit of logic to implement the "invert" function when Button1 on the Combi is selected.

The CV outputs are taken from the "Gate Output" Spider Splitter. The SplitA output is the normal or inverted output, while the SplitB output is always the inverted output.

Figure 6

Figure 6 shows the gate activating when the Modulator Wheel on the Combi is set within the two thresholds. Both Thor Buttons are lit. Note the two DDL Delays in the CV Monitor Combi - as the Modulator Wheel is moved, the gate will open or close and the DDL displays will indicate this. A value of 127 on the left DDL shows that the gate is open (i.e. the switch is on). The right DDL shows the inverted output (switch off).

Figure 7

Figure 7 shows the input CV value set by the Modulator Wheel below the Lower Threshold. Only one Thor button is lit, because the input signal is below the Upper Threshold, and the gate is closed (switch is off). The left DDL shows zero. The right DDL shows the inverted output (switch on).

So what can this device be used for?

That is actually a really good question!

One idea is to use a CV input value from a Malström LFO. With several Dual Edge CV Gates, you could divide the LFO range into sections, where each section enables a particular instrument. In this example file, the LFO changes through several waveforms, having a distinct effect on the sound. Note that there is some overlap between each section, so that sometimes more than one SubTractor is audible at a time. It's a bit cheesy, but it works.

Example 1 RNS
Example 1 OggVorbis

Another use may be to select different instruments or effects depending on the velocity of a MIDI note, or to select different effects or signal paths in response to the amplitude envelope of another audio source such a drum loop.

Example 2 RNS
Example 2 OggVorbis

This device is really a solution looking for a problem - a building block towards larger, more complex configurations. So if you have any good ideas for creative uses of this device, I'd really love to hear about them.

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.

Sunday, March 1, 2009

Blog Review: "Reason: Patch A Day"

Robbneu from Reason: Patch A Day very kindly mentioned this site recently, so I thought it would be good to review his site here, since I have been following it myself for several months.

Robbneu updates his site regularly. His goal is to create a new Reason patch, every day in fact, as a means of learning new methods of synthesis and sharing these with his readers. While I suspect real life occasionally gets in the way of such an admirable goal, he's certainly prolific. There are currently over 100 great patches posted since the site began only six months or so ago.

Robbneu obviously spends a fair bit of time creating each patch, and this shows. These aren't your typical trance leads that anyone can create in just a few minutes. Although experimentation and luck can play a large part in designing new sounds, it's clear that he usually has something in mind. Each patch comes with a short description of the inspiration or intended result, and some include suggestions for taking things further. A small RNS file is usually provided to demo the patch, and if it's an effect then the demo may turn the patch on and off to highlightthe change in sound.

The patches are typically of very good quality and sometimes follow a theme. For example, recently the theme was "Saturn's Rings" - a collection of subtle atmospheric sounds that have a definite 'space' feel to them. Other times the patches may focus on a particular synth or effect within Reason, or even a particular type of sound, like drums.

Just to note - you'll need a copy of Reason (full or demo) to hear the patches, as recorded samples are not provided. Patches are developed with Reason 4 although perhaps some would work in earlier versions.

Robbneu was kind enough to allow me to post a patch myself. I thought it would be interesting to imagine a sound and then find a way to create it. I didn't quite end up with exactly the sound I set out to find, but I was pretty happy with what I ended up with.

Summary: a great blog to follow if you like to hear new and interesting sounds in Reason. Regular updates mean there's often something new to download and try out yourself.