We had a requirement to capture very small signals from the auditory system of fish. The fish were to stimulated with sine waves of varying frequency, while recording the second harmonic signal from the auditory system. A SR830 Lock-in Amplifier can be controlled via a serial line. Under computer control, it can vary its output frequency over the audio range and its output amplitude over a factor of 1000. The input magnitude and phase can be directly read back to the computer.

Three programs were produced to:

-- Calibrate the sound source amplitude vs frequency, producing a spreadsheet of magnitude and phase.
-- Play a random order of tones to the fish, while recording the output, then producing a spreadsheet of results.
-- Play fixed frequency bursts to allow the electrode to be placed.