Introduction to Sound Synthesis Routing modulation
Macro controls
A macro control moves several settings at once, each over its own range and in its own direction. One knob can then change the cutoff, resonance, envelope and other settings of a sound together, and the change can be played in real time.
A sound often depends on several settings that should change together: a brighter version of a pad might need a higher cutoff, a little more resonance, a wider detune and a longer envelope, which is more than one pair of hands can change at the same moment. A macro is a single control whose position is sent to each of those settings by a mapping that sets the range it covers and the direction it moves in. Synthesisers and software instruments with macros usually provide a handful of them, and many list them as sources in the modulation matrix, where they behave like any other source except that a person moves them. On a modular synthesiser, a macro is one control voltage sent through several attenuators to several destinations, with an attenuverter in place of an attenuator wherever a mapping needs to be inverted.
The tool below has one macro mapped to five settings of a two-oscillator voice. Each mapping can be on, inverted, so that it moves the other way, or off, so that its setting stays at the middle of its range.
One macro, five settings
One macro control is mapped to the cutoff, resonance, oscillator detune, filter envelope decay and vibrato of a voice playing a repeating phrase. Each mapping can be switched on, inverted or off.
Listen for Sweeping the macro up with every mapping on changes the sound from a dark, short, steady pluck to a bright, long, wide and wavering tone. Invert the decay mapping and the sound gets brighter as the notes get shorter. Switch mappings off one at a time to hear what each contributes to the overall change.
Ranges, directions and curves
Each mapping turns the macro's position into a value for one setting. Its range sets where the setting sits at either end of the macro, so a mapping can move cutoff across its whole range or nudge a detune by a few cents. Its direction sets whether the setting rises or falls as the macro rises, which is how one macro can brighten a sound while shortening it. Many synthesisers also let each mapping follow a curve, so that a setting changes faster at one end of the macro's travel than at the other. In this tool the cutoff mapping is exponential: each 10% of the macro raises the cutoff by the same ratio, about 35%, so equal movements of the macro move the cutoff by equal musical intervals.
Macros in performance
Because a macro reduces a large change to one movement, it can be handed to a physical control: a knob, a modulation wheel, an expression pedal, or the pressure of a key. Software instruments often show their macros on the front panel and hide the dozens of settings they control, which lets a preset be explored by turning a few named knobs. The same approach works in reverse when designing a sound: decide what one knob should do to the character of the sound, and then find the settings that produce it.
Common questions
What is a macro control on a synthesiser?
A macro control is a single control mapped to several settings at once, each over its own range and in its own direction. Turning the macro moves all of those settings together, so one knob can change a sound from, for example, a dark, short pluck to a bright, sustained tone.
What is the difference between a macro and modulation?
A macro is a control that a person moves, and modulation is usually a signal that the synthesiser produces, such as an LFO. In practice the routing is the same, and many synthesisers list macros as sources in their modulation matrix so they can be sent anywhere an LFO can.
Why do macros matter for performance?
A sound can depend on dozens of settings, more than a player can change at once with two hands. Gathering the settings that should change together under one knob, or under a controller such as a modulation wheel or an expression pedal, makes a large change playable in real time.
Published Glossary