INSTRUMENTATION FOR TRANSIENT EVOKED OTOACOUSTIC EMISSIONS ELICITED BY MAXIMUM LENGTH SEQUENCES

A system for recording Transient Evoked Otoacoustic Emissions (TEOAE) for neonatal screening, utilizing Maximum Length Sequences (MLS) for t he generation of stimulus signals, is described. The main advantage of the system is its ability to obtain responses within a very short per iod of time, compared to conventional OAE systems. The actual recordin g time for the MLS system is reduced by a factor of between 10 and 20 for comparable signal-to-noise ratios. Stimulus levels range from 50 t o 90 dB peak equivalent SPL and available stimulus rates are 31, 62, 1 25, 250, 500, 1000 and 2000/sec. A dynamic noise rejection algorithm i s performed during data collection, and, moreover, all sweeps (both ac cepted and rejected) are stored in memory so that the signal-to-noise ratio can be optimized by post-processing immediately after data colle ction. As a result, robust responses can be achieved even if the subje ct is noisy during the test. A new semi-non-linear recording technique is described, combining the benefits from the conventional linear and non-linear recording methods. Examples of adult and neonatal response s under different conditions are provided to demonstrate the value of the recording principle.