Real-Time Analysis
Bent Frederiksen, Jan Soeberg · The Journal of the Acoustical Society of America · 1970
Brüel & Kjær type 3347 real-time 13-oct analyzer is made especially for the acoustical and vibrational field of measurements, for quasistationary periodic and random signals. A bank of 13-oct band analog filters, true rms detectors, and storage circuits make up the analyzing package. This is followed by a digital multiplexer and a logarithmic analog-digital converter featuring both analog and digital outputs. Special emphasis is laid upon the inclusion of a precision and impulse sound-level meter (per IEC 179), as well as perfect syncronism between parallax-free display scope and digital information. The total accuracy of filters and detectors is 0.5 dB. Instrument dynamic range is 150 dB, display range 50 dB. The frequency range is 22.4–45 000 Hz with 32 filters. Furthermore, four weighting networks D, A, B, and C, and a linear network are supplied with detectors suited for wide-frequency measurements. Signal averaging is done by running exponential integrators with three selectable time constants. A time-coincident 13-oct spectrum as a function of time is available, either as a continuously changing spectrum or as a single instantaneous spectrum or as the highest level in each filter band during a given time. Total information-transfer time is 2 msec.