Archaeoacoustics – Acoustics in Creative Spaces: AES/JAMES Conference - Notes
"One of the most exciting branches of the new multi-sensory archaeology is archaeoacoustics, the archaeology of sound. In February 2014, the pioneers of this field met on the island of Malta for their first international conference. It was truly extraordinary." Kate Douglas, features editor of New Scientist writing in the foreword of 'Archaeoacoustics; The Archaeology of Sound'. This 2015 publication from the first International Multi-disciplinary Archaeoacoustics Conference, where eminent and emerging researchers gathered on the island of Malta, to discuss and share methodologies and analysis of this emerging scientific, arts and humanities field: archaeoacoustics. I was fortunate enough to be in attendance for this first international, multidisciplinary conference, it was truly extraordinary.
Archaeoacoustics is a multidisciplinary practice by its nature requiring the knowledge of anthropologists and archaeologists, architects, acousticians, audio engineers and sound designers, historians and musicologists. As a sound designer and audio engineer I came to archaeoacoustics through the study of acoustic ecology and through conversations with archaeologists. Anthropologist Dr. Ezra Zubrow states in 'Archaeoacosutics; The Archaeology of Sound' "Indeed, many of it's practitioners do not even realize that it is a field, albeit a very immature field. Nor do they think of themselves as archaeoacousticians. Rather they consider themselves to be sound engineers, architects, musical historians, ethnomusicologits and practicing musicians to name a few."
Primarily my research is concerned with the recording, analysis and archiving of impulse responses (IR) recorded in heritage and archaeological sites. Generally this requires man made or naturally occurring spaces used by our ancestors such as caves.
An impulse response is the introduction of a relatively short broadband sound such as a controlled explosion and can be generated successfully by bursting a balloon, firing a starters pistol or amplifying an short burst of random noise (White Noise) through a loudspeaker system and recording the results. A more laboratory approach requires the use of a tone generator replaying a full range 20Hz to 20 KHz sine sweep, an electronically generated tone. In order to fully agitate the acoustic space at all frequencies contained in the sine sweep, playback time has usually to be between 10 and 20 seconds and played back through a reference class loudspeaker system. This sine sweep is in turn recorded using a reference class, omni-directional microphone or array of microphones; multi-channel recordings can be digitally processed to produce surround sound and ambisonic reverb algorithms. Because an IR is very short and contains the full audible range of frequencies in a single transient moment a sine sweep needs to be de-convolved in order to ‘squash’ the whole frequency range of the sine sweep into an IR.
Author of ‘Digital Signal Processing: An Introduction’ Tae Hong Park describes an IR as “agitating a system”. In this case the agitation is the introduction of the impulse, the short broadband sound; the system is the acoustic space, a room, a hall, a cave or even within the standing stones of an ancient megalithic stone circle. Once the recorded files are digitally processed and edited they can be played back in a digital audio workstation (DAW) and used to recreate the reverberation characteristics of the space from which they were recorded. Dr. Damian Murphy of the University of York’s department of Electronics is an acoustician who curates Openairlib.net, an IR archive where the IR’s can be auditioned using anechoic recordings. IR’s recorded in heritage, archaeological and other sites of interest is just one facet of Digital Heritage Archiving. Having interviewed Damian in 2014 he re-itterated my own thoughts regarding the need to photographically document the sites sampled in order to provide visual context to sound recreating acoustic signatures which can be otherwise quite abstract to visualise.
How the space inhabited by our ancestors conjures up ideas of how and why these spaces might have been used for their reverberant and resonant qualities has spawned the field of research we refer to as achcaeoacoustics. Sound designers and musicologists may imagine the soundscape of our ancestors and create compositions inspired by these spaces and places.
Two recent projects have included filed recording in the famed Rosslyn Chapel. Known for it’s intricate symbol stone masonry it is a site worthy of acoustic study. The main chapel has a nice sounding reverb, however the masonry does break up the reverberation characteristics and create a defused reverb tail. The crypt however is a much “cleaner” space and the use of vaulted ceilings common in Medieval buildings gives a good liear quality to the reverb.
The second recent field trip took place one chilly November morning, Wemyss Caves. This known as a multi-use site and has been in use from Bronze Age times. Although the caves are the result of relatively recent coastal erosion in geological terms being between 8 and 5000 years old. They are most notable for the largest concentration of early class 1 Pictish symbol carvings. There are a total of 6 accessible caves on site, however due to the close proximity of the shore line trying to achieve uncontaminated impulse responses is nearly impossible due to the constant sound of the tidal waves. Timings for field work does rely on weather conditions and checking tide tables. The one cave that is nearly silent once within is Well cave having a small anti-chamber before accessing the main cave through a small opening. Once in the acoustic characteristic is very calming and almost silent. This cave has no evidence of Pictish symbol carvings and is largely attributed to the lack of natural light. Upon entering this cave the first impression is that the reverberation characteristic should be impressive, it does however not live up to scrutiny and is rather dead sounding, despite being a large dome shaped cave and approximately 8 metres in diameter.
More significant are Court Cave and Jonathan’s Cave, both of which contain the highest number of stone carvings are more acoustically significant. In Medieval times Court Cave gained it’s name due to the local Laird holding court sessions within. One has to use your imagination to visualise how this must have looked as the cave has suffered from a large landslide in the past few hundred years and now has a mound covered in foliage obscuring one half of what would have been an impressive entrance. There is a significant resonant quality that is found at the throat of the cave and it is easily imagined how a Laird sitting in this position would have been able to project outwards toward the cave entrance most effectively.
One possible use of these significant convolution reverb archives is the use in live sound and to this end I collaborated with my colleague in music, Dr Paul Oliver to create Re-imaging Space. A collaborative project put together for Perth Archaeology Month festival and performed live at Perth Museum. Of course any live performance of this nature is subject to acoustic of the performance space and benefits from as much close mic’ing as possible. Here’s a small excerpt of guest gaelic singer and musician Aileen Ogilvie. As a future project Paul and I hope to create an album of compositions using and inspired by the spaces from which the convolutions were created.
To further quote Kate Douglas "How do you listen to the past? Obviously there are no recordings from ancient times, so you need to think laterally. Luckily, the nascent field of archaeoacoustics is not short of creative thinkers..... Not just that, they can create an acoustic fingerprint of a cave using a "sine sweep" - effectively recording the response of the space to a series of scans emitting a rainbow of all audible frequencies."