Dexter

Complex FM / Wavetable Oscillator

Dexter is a complex, 4 operator wavetable oscillator with DX style frequency modulation (FM) and extensive control possibilities. Its large number of possibilities and options enables it to produce a wide range of complex sounds, textures and timbres.

Contents

• Background
• User Guide
• Master Controls
• Algorithms
• Operators
• Wavetable Menu
• Modulation Menu
• Context Menu
• How it works
• Connectivity
• Video Demos

Background

FM synthesis is a technique that is often shied away from due to its apparent complex nature and unfamiliar parameters. This perception usually stems from the bad interface design in the synthesiser that popularised the technique in the 1980s, the Yamaha DX7.

Dexter approaches FM synthesis from a usability perspective, as in all the parameters are brought out and made accessible to the user. It employs the traditional 4 operator, algorithmic approach with some neat twists, such as wavetables, phase distortion and sync in order to broaden the sonic pallet of FM synthesis. Sometimes it can be mellow, pristine and chilled, however with a simple knob twist it can becoming growling, snarling and noisy. Almost all of the parameters can be modulated by control voltages, allowing for easy exploration of FM, leading to new sounds and possibilities.

User Guide

Master Controls

The master controls are the main go-to controls in Dexter for basic parameters such as tuning, chords, algorithm selection and overall shape and brightness.

Algorithms

An algorithm describes how each operator modulates and synchronises another, and to which output they are directed to, via a routing matrix. It can be thought of as a recipe for a particular type of sound, as algorithms are often optimised for particular timbres e.g. metallic, brassy, smooth, vocal etc. Dexter offers 23 algorithms where 12 of these share operators for both voices A and B, and the remaining 11 dedicate operators to either A or B allowing for independent timbres from each voice.

1	2	3	4	5	6	7	8	9	10	11	12

13	14	15	16	17	18	19	20	21	22	23

By default, the algorithms also determine the synchronisation source for each operator, where operators synchronise to their parent operator. This can be changed in the context menu to “neighbour” where an operator syncs to the operator to its right on the panel i.e. 1 → 2 , 2 → 3 and 3 → 4.

Operators

Dexter features 4 operators shared between two “Voices”, A and B. Voice A is able to output chords of up to 7 notes spread across stereo outputs (A L and A R), whilst Voice B outputs a mono signal from “B Out”. Both voices can be independently tuned allowing for multi-timbral patches. The individual operators outputs, OP 1 to 4, tap a signal directly from an operator of either Voice A or B regardless of the chosen algorithm.

Below is a diagram of the controls common to each operator:

Notes:

• All CV inputs operate between 0-10V, are scaled by the attenuverters, and are internally clipped.
• All knobs act as an offset when combined with CV e.g. Operator Level = "Level Knob" + "Level CV1" + "Level CV2".

Wavetable Menu

This menu allows you change the operator’s wavetable (or bank), and the sync and phasor shaping modes / methods.

Dexter features 35 different wavetables, providing a vast pallet of timbres and textures to work with. By default the “Opal” table is loaded, but this can be changed by going to the “Wavetable” page in the settings menu, and turning the blue wavetable knob to select another table. The following list gives a description about each table.

Wavetables

The following lists show the different phasor shaping and operator sync modes.

Shape Modes Sync Modes

Modulation Menus

Dexter features 4 assignable modulation inputs. These two menus allow you to route each modulation input to 13 different operator parameters.

The following table gives all of the possible modulation destinations.

Destinations

How it works

Operators

The operators generate a tone using lookup wavetable synthesis using a rising ramp, known as a read phasor, to read the contents of a table. Waves can be scanned through by cross fading between adjacent tables within the same bank of tables. FM synthesis is achieved by offsetting the read phasor’s value with another signal, effectively speeding up / slowing down the read speed. Whilst this is technically known as phase-modulation (PM) and is not true FM, this still modulates the frequency and gives the same effect. If anything, PM is easier to implement, and it is a standard method in commercial FM synthesizers such as the DX series. To expand the versatility of FM synthesis, the read phasor can be shaped in several ways that can distort and mangle the output waveform. Dexter offers 12 shaping modes. By default, the modulator signal is added to the read phasor before shaping, however it can be added post shaping by engaging the “Post Shpe” button. This allows for an alternative timbre and at times can make the shaping sound more pleasant.

Connectivity

Half of Dexter’s front panel is covered in jacks, where most of these are in fact CV inputs. However, whilst it seems intimidating at first glance, there is a lot a of repetition. The following table describes the functionality of each jack:

Outputs Master Inputs Operator Inputs

Context Menu

This menu is accessed by right-clicking on any blank area of Dexter.

• Panel Style: Changes the colour of the front panel. Useful for when patching in poor lighting conditions.
  • Dark
  • Light
• Operator Sync Source: Sets the hard-wired sync source of all operators
  • Parent: Operators syncs to the operator above it in the current algorithm
  • Neighbour: Each operator syncs to the neighbour to its immediate right, i.e. 1->2, 2->3, 3->4
• Operator Outputs Source: Determines which voice of operators the individual outputs are tapped to
  • Voice A
  • Voice B

Video Demos

Omri Cohen has created this great introductory video for Dexter

Andrew Mercer has created a great set of tutorial videos on how to use Dexter