Controlling Parameters with Control Signals¶

Control signals can be used to control audio modules in two different ways. First, some audio processing modules have dedicated control signal inputs. Examples of these are the VCA and switch modules. In this case, simply wire a control signal output to a control signal input and the connection is made. For modules without a control signal input, a second method is employed. A parameter can be controlled by assigning a control signal to it, just as you would assign an RS-232/485 or analog control to it.

To use the second method, first open the module you want to control with a control signal. Right-click on the parameter to be controlled an choose Assign controller. Click the Add Controller button and then select Internal Control Signal as the Selected Controller. Then click the Select button. A dialog box will come up and allow you to navigate and choose the desired control signal. The ability to automatically assign all non-assigned controls was added by simply right clicking on the module and select the feature from the menu.

Note: Control signals are specified by the name of the module from which they are output. In order to avoid confusion, always use unique names for control modules.

The second method is the most general and flexible way to use control signals. It does have a minor disadvantage in that control signals are updated about every 20ms, while with the first method, they can be updated every sample period (~20µs). Normally this is not an issue due to the fact that control signals tend to change slowly. However, there are cases such as a dynamics module with fast attack times where they may change rapidly. If a control signal controlling a gain is expected to change rapidly, using a VCA module with a direct connection would be preferable to using a Gain module with an Assign Controller connection.

Continuous vs. Boolean Control Signals¶

A control signal may be either a continuous signal, varying smoothly from 0 to 100% or a Boolean signal, either off or on, true or false, 0% or 100%. This analogous to the difference between control voltages used e.g. in old analog synthesizers and digital logic signals. Both types of control signals exist in Symetrix can generally be freely inter-connected. Modules found under the Control Processes heading in Composer deal with continuous control signals while those under control Logics deal primarily with Boolean control signals.

With Boolean control signal outputs, false/off/low/0 results in a 0% output while true/on/high/1 results in a 100% output. For Boolean control signal inputs, typically anything less than 50% is considered to be false/off/low/0. Anything greater than or equal to 50% is considered to be true/on/high/1. Exceptions to this are modules that have hysteresis, programmable thresholds, or programmable output levels and these will be mentioned in the documentation for that particular module.