Electro-Tongue Drum Project

Introduction

This is a project to build an electronic emulation of a Tongue Drum, also known as a tank drum or a hank drum.

I've described elsewhere what my motivation is to build this project. See my post “My 1st Project - Say Hello to the ‘Electro Tongue Drum’” in my blog for more information.

Project Brief

The main features of the electro-tongue drum should be:

• The shape of the instrument should echo that of the acoustic instrument, but should not copy it slavishly. Think of the difference between acoustic and solid body electric guitars: the electric guitar replaces the acoustic's hollow body with a solid piece of wood. A similar approach should be taken for the electro-tongue drum. The instrument should be circular or polygonal in plan view, but should be relatively flat and solid. It is not desirable to introduce a large chamber that could amplify the percusive sound of fingers tapping the “tongues” *.
• The instrument should be operated by means of touch sensitve pads, rather than mechanical keys, laid out in a similar pattern to the real instrument’s tongues. This layout should make the transition between the acoustic instrument and this electronic version as seemless as possible.
• Ideally there should be two modes of operation:

  1. Audio Mode where the instrument produces sound when a tongue is touched. The sound may be reproduced via an internal speaker and/or sent to a line level audio jack for external amplification. A headphone output may also be provided.

     A decision is required as to whether the sound should be synthesised or created by triggering samples of a real acoustic instrument.

  2. MIDI Mode where the instrument outputs MIDI messages in response to tongue hits. Such messages should be suitable for interpretation by any physical or virtual instrument capable of being driven by MIDI, It is desirable that the generated MIDI should be compatible with as many tongue drum virtual instruments as possible.
• The instrument should be capabable of stand alone operation.

* – A “tongue” on a tongue drum is the area that the player strikes to create a note. This is analgous to a key on a keyboard.

Progress

This is a long term project and I am very inexperienced, having just begun to learn electronics in April of 2021. Progress is expected to be slow.

The project is very much in the experimental phase. Having determined that the touch sensitive “tongues” are to use capacitive sensing, experiments are being conducted to learn about suitable material and software.

Experiments

To date, these are the experiments that have been conducted:

Design Decisions

Number of tongues

Research has indicated that both eight and nine key tongue drums are popular, so it has been decided to construct the electro-tongue drum as a nine key instrument.

A nine key tongue drum has a central tongue and eight outer tongues around the circumference of the instrument. The following image illustrates the layout:

The eight key tongue drum has the same layout as the nine key version, except that the centre tongue is omitted. In a later version it is proposed to offer an option to switch the instrument into eight key mode by disabling the centre tongue.

Note order

The notes will be laid out in accordance with standard tongue drum practice.

To illustrate let us label the outer tongues according to their compass positions. The lowest note is on the centre tongue, then the notes increase in pitch is this order: south, south-west, south-east, west, east, north-west, north-east and finally north.

The following diagram shows the notes labelled in ascending pitch order from 1 to 9.

Notice that no scale has been specified here, only the order in which pitch ascends (and by inference descends) across the tongues. The matter of scale and tuning will be addressed next.

Tunings

First some facts about the tuning of acoustic tongue drums:

• Acoustic tongue drums are tuned to a pre-determined scale.
• Some manufacturers offer their instruments in a choice of scales.
• Some tongue drums can be re-tuned.
• Some notes from the scale may be omitted, particularly when the notes span more than an octave. For example, all five notes of a pentatonic scale may be present in one octave but maybe only the tonic, 3rd and 5th may be present in a higher octave.

Since the electro-tongue drum will generate its notes artificially, there is no reason why a number of scales can't be supported.

Here's a possible roadmap identifying how such a feature may be added, depending on mode: