Virtual Acoustic Technology (VAT)

 

McGill’s Virtual Acoustic Technology (VAT) offers new solutions in the key areas of performance by focusing on the electro-acoustic coupling between existing room acoustics and simulation acoustics.

Background

An innovative electro-acoustic enhancement system, based on measured high-resolution impulse responses, is currently in development at the Virtual Acoustic Technology (VAT) Lab of McGill University. Since 2005, the research team at VAT Lab has measured high-resolution room impulse responses of various acoustic spaces. Consisting of 2 sub-woofers, 2 super-tweeters and many other types of speakers, between 8 and 14 loudspeakers are placed in a room to generate slow logarithmic sine sweeps. The acoustic responses are then captured in an 8-channel surround microphone configuration with 2 height channels at 32bit/96kHz resolution. The virtual acoustic response is created using a low-latency hardware convolution engine and a three-way temporal segmentation of the measured impulse responses.

Development

The first model is installed in the Multi-Media Room (MMR) at McGill University’s Schulich School of Music, a large rectangular space (80ft x 60ft x 50ft) designed as a film scoring stage. The system uses an array of omni-directional radiators within the room; its signal processing includes 24-channel low-latency convolution at 24bit/96KHz, three separate stages of matrix mixing, equalization and time variation. The system of 192 loudspeakers is clustered into low diffraction spheres rendering a homogeneous ambient sound. A lift-equipped grid allows all loudspeakers to be brought up or down to accommodate each type of ensemble, and enhance the auditory presence of the virtual acoustics. All control parameters of the active acoustics are implemented in ‘Space Builder’, a multi-channel sound design engine, by employing multichannel parallel mixing, routing, and processing. The current generation VAT system provides the following key features:

  • Uniform distribution of sound energy within the hall in a wide frequency range
  • Minimized system delay providing immediate acoustic response to the musicians
  • Ability to individually control direct, early reflections (ER), mid and late reverberation
  • Ability to provide direct, ER, mid and late reverberation to any location in the hall
  • System stability with low risk of feedback and minimal sound coloration

Evaluation

Field tests are currently underway at McGill University involving performing musicians and ensembles in order to fully assess and quantify the benefits of this new approach in active acoustics. Musicians receive acoustic support from room models stored in the diverse library of measured architectural spaces. They can blend in desired components of room responses in order to improve their own interaction with the room and other players.

The objective measurement of the system adjusted to improve on-stage acoustics verifies the enhancement of parameters such as inter-aural cross correlation coefficient (IACC), early stage support (ST1), and early decay time (EDT) without excessively increasing the overall acoustic energy in the room. These parameters are responsible for controling subjective aspects of clarity, reverberance and immersion. The subjective evaluations collected from multiple recording sessions with professional musicians using the system show that musicians uniformly agree on the best settings providing the enhanced acoustic conditions for a particular performance. Choral ensemble and string quartets are able to “play the room”, and they find virtual acoustics to be a helpful and enjoyable means for enhancing their musical performance.