Smart.OctaveBands displays the level in each octave or third-octave band as a bar, with the frequency-weighted overall level and a limit curve the bands are checked against. It is the display of a sound level meter and of a vibration survey.

Bands follow IEC 61260 and the A and C weightings follow IEC 61672, so a reading here matches the meter on the bench. Blocks of samples are pushed and analysed with the FFT of Smart.DSP, the power of the bins inside each band summed; an application with a real filter bank assigns the levels directly. Fast or slow averaging settles the bars the way a meter's time weighting does, and peak hold keeps the highest level of each band.

A compressor room, in dB SPL

A microphone at the operator position, 48 kS/s, calibrated in pascal, with the A weighting on and the noise limit of the site's hearing conservation plan as the dashed curve. The compressor's 2x line frequency hum at 100 Hz and its blade passing tone at 1.25 kHz stand out; open the door to the compressor and the bands above the limit turn red. The overall level is the sum of the bands on energy.

Levels from a filter bank

A vibration survey of a gearbox in whole octaves, from a hand-held analyser that reports the band levels itself: the levels are assigned, not computed. The limit is per band, from the machine's acceptance specification.

The overall level in the header is a status line, so a screen reader hears it change. Every band's level is available as text under the plot, and the plot's label names the overall level and the highest band.