1/3 - 1/1 Octave Filter Set Type 1625 A portable Band Pass Filter Set primarily intended for use with Sound Level Meter Type 2230, 2231 or 2233. Permits third-octave frequency analysis, and octave frequency analysis with a step of octave or third-oc-tave. Fully automatic recording of the analysis is possible with a Level Recorder Type 2317, 2306 or Type 2309. The scanning of the filter and the Level Recorder are fully controlled by the Filter Set to obtain an optimal recording. Two scanning speeds are available for analysis of levels measured with "Slow” or "Fast" time weighting. The selectable centre frequency range is from 20 Hz to 20 kHz and a linear position gives a frequency band from 3 Hz to 75 kHz. The analysed signal may also be weighted by selecting “A” or “C” frequency weightings on the Sound Level Meter.