The Huge Microphone Array(HMA) project started in February 1994 to design, construct, and test a real-time 512-microphone array system and to develop algorithms for use on it. Analysis of known algorithms showed that signal-processing performance of over 6 Gigaflops would be required; at the same time, there was a need for ''portability'', i.e., fitting into a small van. These tradeoffs and many others have led to a unique design in both hardware and software. This paper presents the design and its justifications. Performance data for a few important algorithms relative to usage of processing-capability, response latency, and difficulty of programming are discussed.

Structure in the current-voltage characteristics of tunneling junctions is very clearly revealed by displaying the second derivative of current with respect to voltage (d2i/dv2) as a function of junction bias. Equipment for doing this was first described by Thomas and Klein. This paper describes an alternate approach to the recovery of the first and second derivatives using a transistorized electronic circuit which, in addition to being compact and rather inexpensive, provides as good, if not better, resolution than that previously reported. The current-voltage characteristic of a typical silicon tunnel diode at 4.2°K and the first and second derivatives of this characteristic using the apparatus described are given.