title: Audiophile hardware in vision science; the soundcard as a digital to analog converter.
abstract: The design objective was to develop an inexpensive digital to analog (D/A) converter for use in vision science. Soundcards are hardware units that can be integral or can be added to a computer to add sound capability. A soundcard contains D/A converters designed to work in the audio frequency range, typically 20-20,000 Hz. Soundcard outputs are high-pass filtered and thus do not convey sub-audio frequency or dc information. It is possible to circumvent this design feature by programming the desired output waveform as an amplitude modulation of a high frequency carrier, and then demodulating the soundcard output. The circuit, using a 20 kHz carrier, provides precise D/A conversion for the frequency range relevant for vision experiments, dc to 100 Hz, using inexpensive readily available components. The specific application was for 8 channels of D/A conversion using a Macintosh computer running under OS X. The software needed to program stimuli was created using CoreAudio, a library for programming sounds in OS X. Using soundcards on other platforms would not be a problem, as long as there exists a low level library that would enable the wave table to be filled.
authors.affiliation: Department of Ophthalmology and Visual Science, Visual Science Laboratories, The University of Chicago, Chicago, IL, USA.
authors.forename: Marco J H
authors.initials: MJ
authors.lastname: Puts
authors.forename: Joel
authors.initials: J
authors.lastname: Pokorny
authors.forename: Jules
authors.initials: J
authors.lastname: Quinlan
authors.forename: Linda
authors.initials: L
authors.lastname: Glennie
mesh_terms: D001921:Brain / Q000502:physiology; D016287:Computer Peripherals / Q000191:economics / Q000592:standards*; D004581:Electronics / Q000295:instrumentation / Q000379:methods; D004594:Electrophysiology / Q000295:instrumentation* / Q000379:methods; D009482:Neurophysiology / Q000295:instrumentation* / Q000379:methods; D010775:Photic Stimulation / Q000295:instrumentation* / Q000379:methods; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D012984:Software / Q000592:standards / Q000639:trends; D013016:Sound; D014796:Visual Perception / Q000502:physiology