A Text-to-Drumbeat App
https://jxxcarlson.github.io/app/drumlanguage.html
Some time ago, I read James Gleick’s book The Information: a History, a Theory, a Flood. In the first chapter, he recounts a remarkable discovery by John F. Carrington, an English missionary, who took up residence in the Congo in 1938, working for the Baptist Missionary Society. On a trip from the Society’s Yakutsu station on the Upper Congo River through the Bambole Forest, he realized that the local people were able to use drums to send detailed messages over long distances. Here is a short extract of a funeral announcment:
La nkesa laa mpombolo, tofolange benteke biesala, tolanga bonteke bolokolo bole nda elinga l’enjale baenga, basaki l’okala bopele pele. Bojende bosalaki lifeta Bolenge wa kala kala, tekendake tonkilingonda, tekendake beningo la nkaka elinga l’enjale. Tolanga bonteke bolokolo bole nda elinga l’enjale, la nkesa la mpombolo.
In the morning at dawn, we do not want gatherings for work, we want a meeting of play on the river. Men who live in Bolenge, do not go to the forest, do not go fishing. We want a meeting of play on the river, in the morning at dawn.
It took Carrington some time to decipher the secret of the drums. The key fact was that the local language was a tonal one, with two tones, high and low. The drummers, using slit drums, would sound the tones of the words to be sent. Thus alambaka boili, meaning “he watched the riverbank,” was rendered as H L H H L L L, where H is a high-pitched sound and L is low-pitched. While much information is lost in this pitch encoding, that which remains, plus the context, plus the use of many conventional formulae, gives the listener enough information to reconstruct the original sentence.
A Drum App
Inspired by this story, I decided to make a little app to do something similar. You can see a screen shot below. There are two windows, Voice 1 and Voice 2. The first plays in quarter notes, the second in eighth notes. Text in each window is translated into notes via an algorithm we describe later. For example, the text ,,,Hey jude is translated as Rest Rest Rest G3 C3 C3 Rest D4 C3 Bf3 C3, where spaces and commas are mapped to rests. The notes G3 and G4 are the note G in different octaves, and Bf is B-flat. Etc.
Note the period of the two voices taken together. In the case of the voices in the screenshot, the period is 1800 eighth note beats — the least common multiple of twice the length of voice 1 and the length of voice 2 (For this purpose we count in eighth notes). In this way two short fragments, one for each voice, can produce music with a long period — the smallest number of eighth notes before the music repeats.
Mapping text to sound
My approach for generating sound was to map each letter a–z to a phonetic class, then map phonetic classes to musical pitches. The phonetic class of a, e, i, o, u is VOWEL. Consonants are divided into various classes, e.g., m, and n are of class NASAL. Each class is assigned a pitch, and so we can map any string of characters to a sequence of pitch names. For example, Hello is assigned the sequence G3 G2 C3 C3 G2. Here the numerical part of a pitch name refers to its octave, and so G3 is one octave higher than G2. The pitches used to represent the pitch classes are G2 C3, E3, F3, G3, Bb3, D — a dominant ninth chord. This choice of mapping makes the drumming sound relatively harmonious.
Postscript
Gleick writes that Carrington eventually learned to drum, mainly in Kele, a Bantu language in what is now Eastern Zaire. He recounts this story:
A Lokele villager said of Carrington “He is not really European, despite the color of his skin. He used to be from our village, one of us. After he died, the spirits made a mistake and sent him off far away to a village of whites to enter the body of a little baby who was born of a white woman instead of one of ours. But he belongs to us, he could not forget where he came from, and so he came back. If he is a bit awkward on the drums, this is because of the poor education that the whites gave him.”
There is much more in Gleick’s book. It is a really good read.
More info
For more information, see the (open source) code and the README document at
https://github.com/jxxcarlson/DrumLanguage
The code for the app itself — user interface, parsing of the input, translating the input into a form that Tone.js can understand —is written in Elm, a language of pure functions (https://elm-lang.org).
The Tone.js library is used for sound generation. Take a look at the README file at https://github.com/jxxcarlson/DrumLanguage for more details.
