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SPL Response Select

Controls: Options >> Sound Level Meter >> Fast, Slow, etc.
Macros: SPL_TC=Fast, Slow, Quasi, PPM, Custom

These five radio pushbuttons allow selection of the time response characteristic or "damping" to be applied to the Sound Level Meter display.

The names and response characteristics can be changed as desired. Default names and responses are:

Fast = 125 msec single time constant, no peak detection.

Slow = 1000 msec single time constant, no peak detection.

Quasi-Pk = 30 msec Attack, 1000 msec Decay. This will give an approximation of the ITU-R 468 single-burst response for bursts less than 20 msec, but will read too high on long bursts. This is because the Sound Level Meter operates on the spectrum computed from 1024 input samples at a time... about 21.3 msec at a 48000 Hz sample rate. If a burst is shorter than that, its spectral energy is reduced proportionally. If the Attack value is increased to about 180 msec, the response will approximate the specs for long bursts, but short bursts will read too low.

PPM (BBC Peak Programme Meter) = 4 msec Attack, 1000 msec Decay (-26 dB in 3 seconds).

Custom = 100 msec Attack, 10000 msec Decay.

Macro Notes:

You can set the time constant via button index or name. For example, either SPL_TC=0 or SPL_TC=Fast select the top button.

    0 = Fast
    1 = Slow
    2 = Quasi
    3 = PPM
    4 = Custom

Index values can be set from variables or expressions, and can be tested in IF statements.

Note that if you use a name in an IF test, it must be in quotes: IF.SPL_TC="Fast"

Note that these are the only response names that can be used for macro control, even if you have changed the names that are actually shown on the buttons.

See also Sound Level Meter, Response Time


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