Signal Presentation System and ABR Testing
International Acoustic Eclipse 25 (Denmark) were used as the recording system. Blackman gated 1kHz tone-pips with three different durations of 1ms (S1), 2ms (S2) and 3ms (S3) were used with stimulus repetition rate of 27.1/second, sweep number of 1024, amplifier gain of 100k and band pass filter from 300 to1500Hz. Non-invasive button electrodes were used: recording electrode was at the forehead hair line, the reference electrode on ipsilateral cheek of the tested ear and ground electrode on the nasion. Skin was wiped with 95% alcohol to ensure the inter-electrodes impedance was lower than 3kΩ. The sound source was put 30cm away from the external ear canal whose central axis was in line with that of the loudspeaker.