Fast, Slow and Impulse sound levels
Most sound level meters have two exponential time-weightings, F = Fast and S = Slow.
Some also have an impulse time-weighting, a quasi-peak detection characteristic with a rapid rise time and a much slower decay.
F : Fast Sound Level = 125 ms rise and decay time
S : Slow Sound Level = 1 second up and down,
I : Impulse Sound Level = 35 ms while the signal level is increasing and 1.5 seconds when the signal level is decreasing.
Sound Level time-weightings are also known as sound level time constants
Back to the days of simple analogue meters, these time-weightings were introduced to give the operator chance to 'follow' the rapid meter fluctuations by eye.
Peak : Peak-to-Peak : P-P : True Peak : Lpeak : Lpk etc.,
Peak should not to be confused with Lmax which is usually measured with a Fast weighting.
To measure the true peak values a sound level meter must be equipped with a peak detector, which according to the International Sound Level Meter Standards, should responds in less than 100µs. The typical response time for a Class 1 meter is 40µs (40 microseconds).
Peak Hold is a peak detector which retains the 'true' maximum value of a signal.
Peak Sound Level is the maximum instantaneous sound pressure level during a measurement.
Peak Sound Level Definition (IEC 801-22-15) greatest instantaneous value of a standard-frequency-weighted sound pressure level, within a stated time interval, also known as the peak frequency-weighted sound pressure level.
Note : If frequency weighting is not specified, the A-frequency weighting is understood.
Peak Sound Pressure