Acoustic bandlimiting filters for digital conversion of signals

Abstract

Analog‐to‐digital conversion is required for digital processing of signals in a number of areas of acoustics. Examples include voice communications, underwater sound, acoustic imaging, and room acoustics. For each such signal, analog bandlimitation (prior to sampling and quantizing) is necessary to prevent aliasing distortion. Typically, the bandlimitation is accomplished by electrical filtering. As the cost of integrated digital logic diminishes, the expense of electrical filtering becomes a significant part of the total conversion cost. Similar factors apply in the desampling operation, or digital‐to‐analog conversion. We report here a design technique for acoustic filters which can perform the requisite band limitation. The filters can be made an integral part of the transducer assembly, both for transmitter and receiver. We present theoretical designs for fourth‐ and sixth‐order low‐pass filters that are appropriate for voice digitization, and we evaluate these designs by computer analysis. Next, we s...