How to Perform Acoustic Measurements at the Finnish Rock Painting Sites – A Multimedia Guide

Since 2013, the archaeoacoustic team of the University of Helsinki has been exploring acoustic properties of rock painting sites in Finland, ritual places of prehistoric hunter-gatherers. The rock paintings, comprising figures of elks, boats and humans, sometimes holding drums, are typically situated on vertical highly-reflective cliffs that generate echoes and other startling acoustic effects (Rainio et al. 2014; 2017a–b). As these cliffs rise directly from lakes or rivers, the ritual activities, such as painting, sacrificing or drumming, were probably performed from a boat, some type of dugout or canoe.

To study the acoustics of these hardly accessible, rugged places, new field recording and audio analysis methods have been developed by our archaeoacoustic team. The primary analysis method is multichannel impulse response measurement using custom-built recording equipment tailored to the field conditions at Finnish rock paintings. The in situ measurement data is post-processed with custom-written signal analysis software (Lassfolk & Uimonen 2008; Lassfolk 2013; 2014). This educational audiovisual material shows step by step, how the fieldwork and the acoustic measurements of our project are carried out in practice. Full reports of the methods have been published in earlier research articles (Rainio et al. 2017a; Lassfolk & Rainio 2020). The equipment featured in the videos has been acquired between 2013 and 2019 for the project and entrusted to the University of Helsinki Music Research Laboratory. The videos were shot during the field season 2020 with the Canon Legria HF G26 camera.

Step One: Make a Boat

As the acoustic measurements must be performed at the location of the prehistoric rituals, that is on the lake, a vehicle operating in water is needed. The best solution is to use an inflatable rubber boat that is easy to transport and shift from lake to lake. The rubber boat of the model Talamex GLW300 is assembled at a slipway in the vicinity of the rock painting, as follows: 1) by inflating the rail and prow tubes of the boat with an airpump, 2) by fixing the oars into the oarlocks, 3) by fixing and adjusting the seatbench, 4) by inflating the keel tube of the boat, 5) by tying the mooring line to the prow, 6) by launching the boat, and 7) by fixing the electric outboard motor over the transom. This procedure takes about 10 minutes.


Video 1. Assembling the rubber boat on the field trip to the rock painting of Tupavuori by Lake Vuohijärvi in Kouvola. The electric outboard motor was mounted after the video recording.

Step Two: Make a Raft

While the boat is indispensable for carrying the researchers and the equipment to the study site, it is a too unsteady platform for the most sensible measuring devices. Therefore, a separate floating raft is used to accommodate the microphones and the loudspeaker. The towed raft called Echo Explorer, designed by Pekka Mikael Laine, is assembled at a slipway, as follows: 1) by screwing the central plates and crosswise wings of the raft together, 2) by placing the buoyant canisters at the tips of the wings, 3) by screwing the reeled anchor lines and the upright stands to the tips of the wings, 4) by fixing the custom-built tetrahedron microphone rack to its stand and four omnidirectional Neumann KM 183 microphones to their numbered places in the rack, 5) by fixing the custom-built dodecahedron loudspeaker to its stand and the external loudspeaker crossover to the central plate of the raft, 6) by fitting the microphone array and the loudspeaker with cables, 6) by fitting the microphone array with windshields, and 7) by tying the drag line to the tip of the wing. This procedure takes about 15 minutes.


Video 2. Assembling the recording raft on the field trip to the rock painting of Ruominkapia by Lake Kivijärvi in Lemi. The loudspeaker is not seen in the video, because it was not in use on that day.

Step Three, Option A: Make Noise

At the study site, the raft is anchored to a chosen location in front of the rock painting, the wing with the microphones pointing at the rock. A suitable distance between the rock and the microphones is 20–50 metres. The microphone and loudspeaker cables from the raft are connected to the Zoom F8 and H4n multichannel audio recorders and a battery-powered amplifier situated in the boat. The impulse response measurement, as such, comprises a performance of an excitation signal, either an instantaneous broadband impulse or a sine wave sweep, and the recording of this signal with subsequent reflections generated by the space. The following video shows the option with an instantaneous impulse, in this case, a balloon pop. First, a balloon is inflated to the breadth of 40 centimetres using an airpump and a template. Next, the F8 recorder is switched on and the predefined recording levels are set. At a distance of 5 metres from the microphones, at a windless moment, the balloon is detonated with a utility knife. After listening silently for approximately six seconds, the recorder is switched off and tatters of the balloon are harvested from the water using a net bag.


Video 3. Performing acoustic measurement with a balloon pop at the rock painting of Salmijärvi on Lake Salmijärvi in Vihti. The video was shot with the assistance of Ulla Valovesi.

Step Three, Option B: Make a Sweep

In the following video, a sine wave sweep serves as the excitation signal. The logarithmic sine sweep is played through the omnidirectional dodecahedron loudspeaker using the H4n recorder in the boat as a playback device. When all devices are switched on, the signal sweeps through all audio frequencies heard by the human ear (20–20 000 Hertz) in 10 seconds. Although at the time of measurement, the sweep masks most of the reflections generated by the space, the site’s acoustic response becomes audible in the post-processing phase, in the process of deconvolution. The sine sweep provides an optimal measurement signal because of its repeatability and even dynamic range.


Video 4. Performing acoustic measurement with a sine wave sweep in front of the rock painting of Haukkasaari on Lake Kivijärvi in Lemi.

Step Four: Make Music

In addition to impulse response measurements, it is exciting to test the site’s acoustics with freeform excitation signals, such as human voice talking, singing, hooting or crying and instruments presumably employed by the prehistoric hunter-gatherers. These live experiments help develop and formulate hypotheses about the ancient sound rituals, and the recordings work well for demonstration purposes (Rainio & Shpinitskaya 2020; Shpinitskaya & Rainio 2021). The last video shows a drumming session, in which the beats of a frame drum from the boat bounce off the opposing rock surface, forming thus a duett between the performer and the painted rock. Further demonstrations and digital reconstructions of the site’s acoustics can be created with convolution and auralization techniques (see Lassfolk & Rainio 2020).


Video 5. Beating the drum in front of the rock painting of Olhavanvuori on Lake Olhavanlampi in Kouvola.

 

Riitta Rainio & Julia Shpinitskaya

Sources & Further Reading

Acoustics of Sacred Sites – University of Helsinki Project Webpage: https://www.helsinki.fi/en/researchgroups/acoustics-of-sacred-sites

Acoustics of Sacred Sites – University of Helsinki YouTube Video Channel: https://www.youtube.com/channel/UCatXHVuzyzffUrQ40HtO86A

Lassfolk, Kai 2013. Fourier-muunnos ja spektrianalyysikuvaajien tulkinta musiikintutkimuksessa, osa 1. Musiikin suunta 35 (1): 57–65.

Lassfolk, Kai 2014. Fourier-muunnos ja spektrianalyysikuvaajien tulkinta musiikintutkimuksessa, osa 2. Musiikin suunta 36 (1): 67–72.

Lassfolk, Kai & Jaska Uimonen 2008. Spectutils: an audio signal analysis and visualization toolkit for GNU Octave. Proceedings of the 11th International Conference on Digital Audio Effects (DAFx-08), September 1–4, 2008, Espoo, Finland, toim. J. Pakarinen, C. Erkut, H. Penttinen & V. Välimäki. 289–292. http://legacy.spa.aalto.fi/dafx08/papers/dafx08_49.pdf

Lassfolk, Kai & Riitta Rainio 2020. Suomen kalliomaalauskohteiden arkeoakustinen tutkimus. Musiikki 50/1–2: 17–44. https://docplayer.fi/191873219-Suomen-kalliomaalauskohteiden-arkeoakustinen-tutkimus.html

Rainio, Riitta, Antti Lahelma, Tiina Äikäs, Kai Lassfolk & Jari Okkonen 2014. Acoustic Measurements at the Rock Painting of Värikallio, Northern Finland. Archaeoacoustics: The Archaeology of Sound, ed. Linda C. Eneix. Myakka City, Florida: OTS Foundation. 141‒152. http://hdl.handle.net/10138/164521

Rainio, Riitta, Antti Lahelma, Tiina Äikäs, Kai Lassfolk & Jari Okkonen 2017a. Acoustic measurements and digital image processing suggest a link between sound rituals and sacred sites in northern Finland. Journal of Archaeological Method and Theory 25 (2): 453–474. http://dx.doi.org/10.1007/s10816-017-9343-1

Rainio, Riitta, Tiina Äikäs, Antti Lahelma & Kai Lassfolk 2017b. Nauravat kalliot: Pohjois-Suomen pyhien paikkojen kaikututkimus. Muuttuvat suomalaiset äänimaisemat, eds. Heikki Uimonen, Meri Kytö & Kaisa Ruohonen. Tampere: Tampere University Press. 167‒199. https://urn.fi/URN:ISBN:978-952-03-0382-2

Rainio, Riitta & Julia Shpinitskaya 2020. ”Niin kallio vastaa kuin sille huutaa!” Kaikuakustiikka esihistoriallisilla kalliomaalauksilla. Kalmistopiiri 29.12.2020. https://kalmistopiiri.fi/2020/12/29/niin-kallio-vastaa-kuin-sille-huutaa-kaikuakustiikka-esihistoriallisilla-kalliomaalauksilla/

Shpinitskaya, Julia & Riitta Rainio 2021. Talking Rocks, Illusory Sounds, and Projections of Otherworld: Acoustics of Sacred Sites As a Magic Media in Cultures of Shamanism. Illusion in Cultural Practice: Productive Deceptions, ed. Katharina Rein. Abingdon: Routledge. 165–188.  Supplementary audiovisual material available online: https://www.youtube.com/playlist?list=PLv5RHkY9FT3J_naOwEhGC9nyL7qoPeRoF

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