Ephemeris de la Lune

Ephemeris de la Lune was an extended riff on the 800% slower internet trend, where pop songs are transformed into ambient washes through extreme time-stretching. Tracks by Justin Bieber and others became abstract ambient soundscapes: a kind of musical alchemy in which familiar songs were transformed into something strange and unrecognisable. Indeed, this rather harsh sonority was harnessed in my piece Troy Ounce, where Spandau Ballet’s hit Gold! was stretched and played according to movements in the gold price. It’s not exactly easy listening!

Whilst researching this trend I noticed that pop tracks generally became quite noisy as the transients of drum tracks were smeared by the time-stretching algorithm. In contrast, a version of Beethoven’s Moonlight Sonata, stretched to 800% in a YouTube video selling it as relaxing ambient music, produced something quite different: the solo piano sonority stretched out into long drones, as if the listener were microscopically inside the piano.

At around the same time, while researching potential data sources for sonification projects, I had come across astronomical calculations - the ephemeris of the title. The idea that the passage of the Moon through the sky, as the Earth rotates, could become the playhead or needle on the record followed quite quickly. The calculations are made for an observer in Sheffield, meaning that this particular version of the piece is, quite literally, the Moon as seen from Sheffield. The Moon’s azimuth, measured from 0–360°, would determine how far through the stretched recording we had travelled. Unlike Troy Ounce, this was a one-way piece: the recording simply progresses as the Moon moves across the sky. The piece is deterministic, but never fixed: because it begins wherever the Moon happens to be when it is started, and the subsequent mix is continually shaped by its elevation and phase, each journey through it is different. Unlike Troy Ounce, for instance, where the generative system depends upon the unknowable movements of a financial market, Ephemeris de la Lune uses a system whose behaviour is entirely predictable. Its variability comes instead from the point at which the listener encounters that system.

It turned out that Beethoven’s Ninth Symphony had already been the subject of a time-stretching piece that pre-dated the 800% slower craze: Leif Inge’s 9 Beet Stretch. This put me in something of a quandary, because the simple idea of “Beethoven lasts a day” had already been done. I wanted to introduce more sonification elements beyond simply having the playback stretched. Strictly speaking, extreme time-stretching doesn't require live data at all, other than using the Moon's position to establish the starting point.

Many recordings of the first movement of the Moonlight Sonata are actually playing simultaneously - ten in this version - and are controlled by the elevation of the Moon, from -90° (below your feet) to +90° (over your head). The ten recordings are spaced at 20° intervals across this 180° range. This means that, as the Moon rises and falls through the sky, different recordings come into prominence. The gaps between these positions are dealt with by an amplitude window, so rather than sharp breaks between recordings, a continuous mix is heard. This window itself responds to the lunar phase: around the new moon, when illumination is low, the window is narrow; as the Moon approaches full, it widens, ‘illuminating’ more recordings.

Making the piece for the web, I had the source material to hand, having assembled several of these reconstructions already, and a long-range granular time-stretch was relatively straightforward to implement. There were some compromises. This version features ten voices rather than the original nineteen, to stay within the capabilities of the average browser. The computationally expensive phase-vocoder FFT algorithm is replaced by a simpler granular one.

The recordings are also offset from one another in time. Their starting points are distributed at 36° intervals around the Moon’s 360° azimuth, so that each recording begins at a different point in the stretched source material. This creates another layer of variation as the Moon travels across the sky. At 10° of azimuth, say, we might be near the start of one recording while simultaneously hearing the tail end of another. The result is that the Moon is not simply moving a single piece of music through time, but continuously navigating a shifting constellation of stretched performances.

The original version of Ephemeris de la Lune is documented in my PhD thesis.