Electro-Tongue Drum Project

Introduction

This is a project to build an electronic emulation of a Tongue Drum.

I'm an amateur musician of sorts. I play guitar, write electronic music on my PC, and have a liking for weird and off beat instruments. Canjo anyone? One such instrument is the Tongue Drum (aka Tank Drum, aka Hank Drum):

I fancied buying one, but a decent one isn't cheap, so I couldn't justify the cost given the small amount of use I'd have for it. But how about an electronic emulation of one?

I got the idea when I stumbled across a paper piano project online. The person who built this simply drew the keyboard on cardboard and filled in the keys with pencil "lead". Those pencilled in keys were connected to a wire using a paper clip, of all things, and the wire was attached to an Arduino Uno micro-controller via a high value resistor. The Arduino senses when a finger touches one of the keys and plays a (horrible sounding) note in response. Now this blew my mind! Triggering a circuit just by touching graphite - amazing! So off I went down a rabbit hole looking into the world of capacitive sensing.

Could I try to build my Tongue Drum emulator using touch sensitive keys that would trigger the required note by some means? Possibly. It strikes me there are two ways to approach this:

1. Trigger a sample of a real tongue drum and play it back either through a speaker built into the instrument or via a line output to an amplifier or headphones. Or all the above.

   I found some public domain tongue drum samples that could be used.

2. Trigger a MIDI note and send that via a MIDI port to a sampler or virtual instrument.

   And guess what, I happen to have a couple of MIDI tongue drum virtual instruments on my "studio" PC.

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 often 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 capacitive touch 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, as discussed above:
  1. Audio Mode where the instrument produces sound when a tongue is touched.
  2. MIDI Mode where the instrument outputs MIDI messages in response to tongue hits.
• 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 analogous to a key on a keyboard.

Design Decisions

Number of tongues

Both eight and nine key tongue drums are popular. To gain maximum flexibility 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.

Note order

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

To illustrate let us consider the outer tongues according to their compass positions. The lowest note is on the centre tongue, then the notes increase in pitch in 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 across the tongues. The matter of scales and tuning will be addressed next.

Tunings

First some facts about the tuning of acoustic tongue drums:

• Instruments 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 could be present in a lower octave but maybe only the tonic, 3rd and 5th could be present in a higher octave.

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

Progress

This is a long term, and complex (for me), project and I am very inexperienced. Progress is very slow.

The project is very much in the experimental phase. Having determined that the tongues will 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: