Facilities

Anechoic Chamber

The laboratory contains a large (64 m³) anechoic chamber which is equipped for a whole range of bioacoustic, psychophysical and neurophysiological investigations. The chamber has an insertion loss of better than 30dB for sound frequencies greater than 100Hz rising rapidly to greater than 60dB above 500Hz. It is anechoic down to 200Hz (better than 99% absorption).

The anechoic chamber is equipped with a robot arm carrying a small speaker that can be placed at almost any location on the surface of an imaginary sphere (radius 1.2 m) surrounding a test subject located in the middle of the chamber.

The robot arm :

	is fully automated with micro-stepper motor controllers
	has a placement accuracy of better than 0.1 degrees
	moves at up to 60 degrees per second.

Audiometric chamber

The laboratory also houses a double walled audiometric booth large enough for a range of virtual space localisation experiments as well as more traditional psychophysical procedures. The booth is constructed using the same techniques as the anechoic chamber walls and has a very similar insertion loss.

Stimulus control system

The stimulus generation system is DSP based and capable of generating arbitrary complex signals with a very high degree of control over time and frequency domain characteristics.

The system capabilities include:

	stereo output capable of very high digitisation rates (up to 250kHz)
	a stimulus generation and data capture toolbox which has been developed to work as a plugin component of the MatLab data manipulation and visualisation environment
	off-line and on-line digital manipulation of output signals in real time

Data capture and experimental control systems

Data capture is also A/D based, allowing direct to disk recording as well as extensive signal processing and data manipulation. Impulse response function measurements involve Golay code stimuli and stimulus locked averaging to increase S:N together with on-line display of time and frequency domain (amplitude and phase) characteristics of system responses.

All aspects of the stimulus delivery and data capture systems are fully automated and computer controlled. This results in a highly flexible system capable of achieving highly reproducible bioacoustic recordings.

For bioacoustic measurements the objects being measured (eg human ears) are aligned in the hoop coordinate system using a laser alignment system. In human bioacoustic and behavioural experiments, the position of a subject's head is tracked in real time using a 6 degrees of freedom electromagnetic tracking system with mm resolution and 0.1 degree orientation accuracy.