Trevor Butler visits International Noise Day at the Vienna Institute
Noise is around us pretty much all the time, at different levels and across different frequencies. But how much is good for us? And should we take more care of our hearing. These are questions addressed every year on International Noise Day at the Vienna Institute for Acoustics Research (ISF) of the Austrian Academy of Sciences which invites school parties and interested adults to glimpse some of the projects being undertaken by the scientists at their new premises. The special day was started in 1996 by the New York-based Center for Hearing and Communication (CHC). A caucus of some 26 institutes, the Vienna operation’s primary role is audio research, including in its widest forms and involving some pretty high-level mathematics along the way.
The work is divided into five main clusters: mathematics (theoretical work, including signal processing algorithms); Numerics, which includes acoustics studies; Bio Acoustics (for example, is musical reaction learned or is it genetic?); Phonetics which covers accents and dialects; and finally, hearing, which includes work on impairments, cochlear implants and electroencephalogram; the electrical activity in the brain. I was shown around the various Open Day displays by Katharina Pollack who’s recently returned from seven months of study at Imperial College, London as part of her psychoacoustics PhD studies into Sound and Music Computing.
Our first stop is of particular relevance to hi-fi users. Named Noiseman, the display involved listening, through headphones, at a preferred level and then discovering just how high, and potentially damaging to our hearing system, this can be.
I tried to cheat and actually chose an SPL that was lower than I might typically use; even so the result revealed that I was listening at almost 89dB. The system was then set at a ‘much safer’ level so that I could understand the volume I should be using to protect my hearing.
Michael Mihocic was running a demonstration called 3D listening in a loudspeaker array. He ushered me into a sound-proofed booth with extremely ‘dead’ acoustics and I sat in the middle of a 3D stereo simulation in a 91.4 surround sound system (top of page) capable of simulating room reflections up to 7th-order. The set-up of KEF loudspeakers is able to simulate famous concert hall acoustics and, at the flick of a switch, place the listener in the place of the conductor, one of the musicians or practically anywhere in the audience.
The public day demonstration was in four parts so as to give an indication of what’s possible to achieve by generating spatial sources. This was followed by playback in virtual rooms using part of JS Bach’s Bourrée played on guitar and recorded in an anechoic chamber. The first playback was straight stereo, with no added reverberation and directly in front of the listener. Next, artificial reverb was added and the listener placed in a virtual room measuring 6x4x3 metres and placed some 2m from the guitarist. It was really rather spooky that such a change could be made so quickly and easily, to fool the ear and the brain.
The third example played was to demonstrate speech intelligibility and the one I found most fascinating. Three voices can be heard, mixed and muddled all speaking together in front of the listener. The result is a pretty unintelligible melee. Then, two of the voices are moved (left and right respectively) with the front, central voice repeating the same sentence. All of a sudden, all three voices become distinct and it’s possible to understand what each is saying. Amazing. The researchers also discovered that this works only for those listening with two ears and without hearing impairment.
Finally, in this demonstration, an example from Don Giovanni is used to listen from the perspective of the conductor at the great Vienna Musikvereinssaal (without audience), a listening position not normally heard. The ability to be able to listen to recordings in chosen locations is something that could, one day, be offered to audiophiles.
Current research at the Vienna Institute includes the noise levels generated by Austrian trains, and how it can be effectively attenuated for the sake of those living close to the railway. An elaborate rack of measurement microphones was constructed to create a 64-channel recorder. This showed how, at higher train speeds, the noise from the pantograph on the overhead wires was louder than that generated by the metal wheels on the tracks below. This allowed planners to build higher noise barriers alongside the tracks to better protect residents from noise pollution.
The largest test chamber at the Vienna Institute is being used for HRTF work, Head-Related Transfer Function. This is auditory mechanism for determining the elevation of sound sources, not least to determine where sounds come from and the effects this has on listeners.
An overhead arch of 22 loudspeakers has been constructed and allows measurement and analysis of sounds filtered by the torso, head, and pinna using sinewave sweep tones at different levels and in different positions through the arc. The results could influence how soundtracks are made for movies and to generate a more immersive experience for audiobooks as the listener is placed between the characters rather than simply ‘outside looking in’.
Jason is the name of a head measurement device created to sense brain activity and determine how sounds are processed. For example, researchers can show that an approaching sound is processed much faster than one moving away; this to allow more time for a fight/flight reaction if required and relates to the doppler effect.
One fascinating hands-on display allowed the visitor to view two audio plots and to choose which one replicated the sound played through headphones. With frequency plotted against time, some were harder to work out than they looked, not least the image of the Vienna Institute’s own logo when converted to sonic output.
This is but a glimpse of the work underway at the Vienna Institute and, thankfully, brought down to a level that’s easily understood while being related to everyday practical situations. Behind the scenes, there is extraordinarily deep research underway, much of it in initial stages although we will probably see the fruits of this at future Open Days. I thoroughly enjoyed my brief time and would like to thank everyone there for welcoming me and for their assistance.
Additional photography by Martyn Comley