Audio

Reason CV tutorial

My first project, written in July 2012, was a tutorial series about using (virtual) control voltages (CV) in Propellerhead's Reason software. CV can be kind of mysterious. Different devices seem to vary in how they calibrate or interpret CV signals. For example, the pitch-tracker Neptune puts out a Pitch CV signal that is calibrated to drive Thor's oscillators, but not to match the Sequencer Control note/pitch CV inputs used by other synths. In order to understand and manage these kinds of issues, I developed some analytical tools for looking at CV signals.

This series was written when Reason 6 was current. Reason 6.5 came out just a few months later, with support for Rack Extensions (REs), Propellerhead's proprietary plug-in format. In the following months and years, third-party developers released a number of REs to do all kinds of signal processing on CV signals. These tools make it very easy to do the kinds of manipulations described in this series. Still, you may find these tutorials useful for understanding basic CV signal processing in Reason. And you can still use these techniques even in the most recent versions of Reason.

• Reason CV tutorial 1: Graphic display of control voltages (CV) in Reason. CV signals and audio signals are handled very similarly in Reason. This tutorial shows how to safely route CV signals to an audio track so that signal levels can be measured on audio meters and waveforms can be recorded and displayed in audio clips.
• Reason CV tutorial 2: Control voltages (CV) by the numbers. Calibration of unipolar and bipolar CV signals. Mixing unipolar and bipolar signals using Spider CV. Measuring target parameter response. Converting unipolar to bipolar and vice versa.
• Reason CV tutorial 3: Sequencer Control CV (control voltages). A look at the Sequencer Control CV protocol. MIDI-to-CV conversion with RPG-8, versus with Thor. Calibrating Thor's MIDI-to-CV response. Converting Thor's Last Key CV signal to Sequencer Control.
• Reason CV tutorial 4: Thor as a CV (control voltage) utility, part I. Generating static CV signals; generating CV curves by automating the controls; merging, mixing, splitting, and phase inverting CV signals; multiplying CV signals; gating CV signals; converting bipolar to unipolar and vice versa

Some clarifications

2019-10-31

The UIs of Reason devices and REs have various controls that represent CV sources and targets — knobs, sliders, modulation matrixes, etc. These may be calibrated as integer values 0-100, 0-127, -64 to +63, etc. Or they may be shown as floating-point values 0.0 to 1.0, -1.0 to +1.0, etc. It is important to keep the following points in mind:

• CV signals, even sequencer control note/gate signals, are always represented internally as floating-point values. Reason's CV implementation models Continuously Variable Control Voltages as implemented on analog synths.
• A CV source that is calibrated 0-100 or 0-127 actually sends out floating-point 0.0 to 1.0. If the knob is manipulated or automated, the floating-point output may be quantized (stepped).
• CV sources such as LFOs and envelope generators will typically put out a continuous signal.
• CV signals are not restricted to a ±1.0 range. They can take any floating-point value.
• However, CV target devices may interpret CV signals in various ways. For example, out-of-range signals may be truncated to a range of 0.0 to 1.0, or the incoming signal may be quantized to nominal integer values.
• Sequencer control note/gate signals nominally represent integer values 0-127, which may be MIDI notes 0 to 127 (C-2 to G8) or velocities 0-127. However, these signals are still implemented as floating-point values 0.0 to 1.0. Devices like Matrix and RPG-8 send out floating-point values, even though sequencer control inputs on target devices will interpret them as quantized to integers.
• Sequencer control note inputs can receive any CV signal as input. However, these signals are quantized to MIDI note values 0-127. So if x represents the CV signal level, there is a quantization function such that q(x) = MIDI note number. For example,
  • q(0.0) = 0 = MIDI note C-2
  • q(0.5) = 63 = MIDI note D#3
  • q(1.0) = 127 = MIDI note G8
• A sequencer control note input will typically quantize a continuously varying unipolar CV input to MIDI notes on the tempered chromatic scale from C-2 to G8.
• Reason synths such as Thor, Europa, Complex-1, and the Neptune device use a separate bipolar Pitch CV protocol to control pitches of oscillators. Pitch CV is a bipolar, floating-point CV signal centered on C3 (MIDI note 60). It is available from the KeyNote mod source in Thor, the Key mod source in Europa, the Key source in Complex-1, and the Pitch CV output in Neptune. It is also produced by step sequencers in Thor and Complex-1 in note-quantized form. Complex-1 has a Quant2 module that quantizes any bipolar CV signal to chromatic Pitch CV values. Complex-1 can be used to convert unipolar Sequencer Control Note CV to bipolar Pitch CV by routing the Key source to a CV out. Similarly, Thor's mod matrix can do this conversion by routing the KeyNote or LartNote mod sources to CV outs.
• Don't overlook Reason devices such as Thor, Europa, Grain, and Pulsar for manipulating CV. These have back-panel CV inputs and outputs, mod matrixes for combining and manipulating signals, and CV signal sources such as envelope generators and LFOs.
• To visualize what is happening with CV signals, use metering and signal-monitoring tools such as the following:
  • Skope
  • Skope M4
  • Scope Jr (free RE)
  • CV-2 Meter (free RE)