A÷B×C

1. A Input Numerator input, with scaling knob to its right (light gray).
2. A Constant Knob Constant value added to the numerator input.
3. B Input Denominator input, with scaling knob to its right (light gray).
4. B Constant Knob Constant value added to the denominator input.
5. Error Indicators The LEDs turn on when the inputs don’t match the rules.
6. C Constant Knob Scaling factor.
7. CV Output Result of A÷B×C, guaranteed to be between -C and +C.

Overview ⚓︎

This module does a limited division of two CV signals (A and B), and scales the result by a constant (C).

The CV A and CV B sections have a CV input with an attenuverter (light gray knob) to adjust the input signal level between -100% and 100%. The dark knob sets a constant voltage which is summed to the input.

The C knob sets a constant voltage that serves as a scaling factor for the output signal. For example, if C is set to 5V, then the output is guaranteed to be between -5V and +5V.

Each section has a level meter to display its current value.

The A÷B×C module operates at CV rate, so we don’t recommend connecting audio signals to its inputs or outputs.

Limits ⚓︎

The modules doesn’t implement a true division because the Multiphonics signal path emulates that of an analog synthesizer, where voltages must be kept within a reasonable range.

The two limits are:

• The absolute value of the numerator (A) is not allowed to be greater than the absolute value of the denominator (B). In other words, the result of A÷B will always be between -1 and 1, so that after scaling by C the output of the module is guaranteed to be between -C and C. This prevents the module from generating extreme voltages. The |B|<|A| error LED will turn on when the inputs don’t match this rule.

• The result of a division by 0 is 0. This is a bit arbitrary, but works well in practice in the kind of patch for which the module was designed. The Div by 0 LED will turn on if B is 0.

Usage ⚓︎

This module is a companion to the RMS and Envelope Follower, to help building compression algorithms. By inverting the envelope detected by those modules, we get a CV signal that can be used to control a VCA.

Example ⚓︎

Here is an example of the simplest possible limiter patch (you can find it in the Multiphonics CV-2 Effect library under All Patches/Basics/Simplest Limiter):

In this patch, the Envelope Follower Attack knob is set fully counterclockwise to follow the signal peak as closely as possible because we need to detect when the peak crosses the threshold.

The A÷B×C module inverts that envelope: the numerator (A) is set to 5, and the denominator (B) is the signal envelope. C is set to 10 so that the module output is scaled to control a VCA (unity gain at 10V).

The choice of 5 for the value of A is not random. It ensures that only signals above 5V will be limited:

• As we saw earlier, when B < A, the output is clamped to the value of C (10V). So when the input signal’s peak envelope is below 5V (A), the VCA is at unity gain and does not affect the signal.

• When input signal rises above 5V, the output of A÷B×C starts going down, and the VCA lowers the signal volume.

This patch is surprisingly versatile. It can be used as a peak compressor with no changes:

• The Envelope Follower Attack and Release knobs control the response time.
• Both the A constant knob or the Envelope Follower Gain knob can control the threshold.
• The volume on the Input module is a pre-gain.
• The volume on the Output Mixer is a compensation gain.
• The Output Mixer Dry/Wet knob is a good stand-in for a compression ratio knob, from 0 to infinity.