Glossary

Measured values and notation

SPL Sense and SPL Cloud write measured values as is common in acoustics:

The letter after the L is the frequency weighting (A, C or Z), followed by the type (eq or Fmax) and then the time. A prime ′ stands for minutes. The unit is always dB.

CSV exports and PDF reports partly still use an older notation for the same values.

Terms A–Z

A, C and Z weighting

Filters that weight the frequency spectrum. A roughly corresponds to human hearing at low levels and strongly attenuates bass; the equivalent levels of the V-NISSG and of DIN 15905-5 are given in dB(A). C attenuates bass only slightly and shows how much low-frequency energy is involved; DIN 15905-5 uses it to limit the peak level. Z is unfiltered (zero). SPL Sense always measures all three.

Assessment level (Lr)

Term from DIN 15905-5: the LAeq over 30 minutes at the immission location, in blocks starting at every full and half hour. The permissible value is 99 dB.

Audience noise, extraneous noise

DIN 15905-5 calls everything that does not come from the sound system Störschall (extraneous noise), for example audience or pyrotechnics. See Audience noise.

Calibration

Adjustment of the sensor against a reference sound level. It has an expiry date. See Sensor and calibration.

Correlation

For the leveler, the ratio between measured and expected level. 1.000 means: only the sound system can be heard. Values above 1 indicate additional noise, for example from the audience.

Day boundary

Time at which a measurement day ends: between midnight and 06:00.

Deviation, exceedance

A value has exceeded a threshold of the value profile. The measurement details show them per day.

Excluded time range

A period that does not count for maxima, rating and deviations, for example the system tuning. The data is kept and shown greyed out.

Fast (F)

Time weighting of 125 ms. Reacts quickly to peaks. Basis for LAFmax.

Gain reduction (GR)

How many dB the leveler is currently reducing the volume by. Always 0 or negative.

Instance

An installation of SPL Sense registered with SPL Cloud, for example a laptop or a Raspberry Pi.

Interval

A recorded section of one minute. It contains all values of that minute and is digitally signed.

Job

Groups several measurements in SPL Cloud, for example all measuring points of a festival.

LAFmax, MaxF

The highest level with time weighting Fast within the chosen time. The V-NISSG limits LAFmax to 125 dB(A).

LCpeak

C-weighted peak sound pressure level: the highest instantaneous value of the sound pressure, without time weighting. DIN 15905-5 limits it to 135 dB. Not the same as LCFmax: there, the level is first smoothed with the time weighting Fast (125 ms), and the highest of these values is taken. Short peaks therefore come out lower; LCpeak is always equal to or higher than LCFmax.

Leq (equivalent continuous level)

The energy average of the level over a given time. A short, very loud moment raises the Leq considerably; a quiet moment lowers it only slightly.

Leveler

Automatically controls the volume of the sound system so that the limit is met.

Line offset

For the leveler with audience compensation: the difference between the level at the sensor and the signal level at the output of the audio processor, measured without audience.

Live screen

Large display of the current values, for example for the DJ or the technicians. Layout freely configurable.

Loudest place, immission location

The loudest place in the audience area, at ear height. This is where the limit applies. The V-NISSG calls it Ermittlungsort. DIN 15905-5 calls it maßgeblicher Immissionsort (relevant immission location) and distinguishes one for LAeq (determined by mid and high frequencies) and one for the peak level (determined by the bass). See Measuring point and offset.

Measurement

A measuring point with its settings and all recorded data. Can run over many days.

Measurement day

A day of a measurement, delimited by the day boundary. The Pro billing also counts measurement days.

Measuring position, substitute immission location

Where the sensor actually stands, for example at the mixing desk. DIN 15905-5 calls it Ersatzimmissionsort (substitute immission location).

Offset, correction value

Value in dB added to each measured value to infer the level at the loudest place from the measuring position. One value each for A, C and Z. In DIN 15905-5 they are called correction values KA and KC.

Operator PIN

Protects SPL Sense against changes. The live screen remains accessible without PIN.

Organization

A company, a venue or a festival in SPL Cloud. It owns measurements, jobs and instances; several people work together in it.

Pink noise

Test signal with equal energy per octave. Used to determine the offset and line offset.

Read access

Allows another person to view a measurement or a job in SPL Cloud without changing anything.

Recovery zone

Area where the audience can recover from the noise (Ausgleichszone). The V-NISSG requires it for events with an hourly level above 96 dB(A) that last longer than three hours.

Signature

Every interval is digitally signed. This makes it possible to prove that the data has not been changed.

Spectrum, third-octave band

The level split by frequency, in third-octave bands. Visible in the interval details and on the live screen.

Value profile

Defines which values a measurement calculates (e.g. LAeq 60′, LAFmax 1′) and which thresholds apply. Each value has up to three levels: Notification, Warning and Limit. See Value profiles.

Weather protection filter

Compensates for the effect of a weather protection on the microphone. Must match the weather protection used.