Algorithms for the generation of complex sounds for auditory physiology studies

The pallid bat (Antrozous pallidus) is a member of a small class of bats known as gleaners. These bats use echolocation to avoid obstacles in flight while using passive listening to localize terrestrial prey. The echolocation pulses are 60-30 KHz downward frequency modulated sweeps that last 3-5 milliseconds. The prey-generated sounds are broadband noise transients in the 5-35 KHz range [1]. The frequency components of these sounds are beyond the range of commonly available sound cards, but the availability of fast, low-cost computers makes it possible to use host-based digital signal processing techniques to generate more complex sound patterns using existing equipment. The new capabilities allow new types and combinations of behaviorally relevant sounds to be generated, permitting the functions and topology of the auditory cortex to be mapped with increased detail. This paper describes the algorithms used to generate the amplitude and frequency modulated tones and band-pass filtered noise signals used as stimulus sounds.