85 Db Spl Standard Reference - PRESONUS Central Station Plus Owner's Manual

Owner's Manual
3.3.2

85 dB SPL Standard Reference

12. Test: Play audio through Speaker A only. Without adjusting any of the Central
Station's levels, toggle Speaker A off and Speaker B on. You may hear a slight
tonal variance due to the different acoustic properties of the monitoring
systems but the loudness should remain the same. If the loudness varies
drastically, you may wish to repeat this calibration procedure from step 1.
This method of speaker calibration references a specific "standard" meter reading to a
certain acoustic level. This is the most technical, least subjective method and is good
for studios where a specific type of audio is produced or where an industry-standard
audio level exists (such as for film or broadcast). One of the most common calibration
standards (and the one presented here) is -20 dBFS referenced to 85 dB SPL.
NOTE: dBFS means "decibels full scale" and is associated with decibel amplitude
levels in digital systems where there is a finite maximum available level (such as in
standard PCM encoding). The maximum level possible is referred to as "0 dBFS. " In
digital systems with analog outputs (such as digital interfaces), the analog-to-digital
and digital-to-analog converters (ADCs and DACs) are referenced so that 0 dBFS
equals a certain amount of analog voltage. (For example, a 0 dBFS tone playing
at unity gain from a FireBox measures +18 dBu, while a 0 dBFS from a FireStudio
Project at unity gain measures +10 dBu.) It is important to know your digital
devices' 0 dBFS reference to prevent clipping and to aid in proper calibration.
1. "Zero" the Speaker, Main, Cue, and Phones levels by
turning them fully counterclockwise.
2. Select the TRS1 Main Source and Speaker Output A.
3. Turn your primary monitoring system's (connected to Speaker
Output A) input level to its lowest setting. Consult your monitor
system's user manuals or the manufacturer's Web site for more
information about adjusting the input or amplification level.
4. Remove all effects processors (EQs, compressors, reverbs, etc.) from the
signal path and play 500 Hz to 2.5 kHz, bandwidth-limited pink noise at
-20 dBFS through your primary audio source outputs. If you are calibrating
a subwoofer, use 40 Hz to 80 Hz, bandwidth-limited pink noise.
You should not hear the test tone. If you do, turn down
the speaker volume and repeat Step 1.
5. Pan the test tone so it only plays in the left speaker (hard left).
6. Turn the Main level knob to Unity Gain by turning it fully clockwise.
7. In the Passive Speaker Control section, locate the Speaker Trim controls
for L/R Output A. Using a flat-head screwdriver, turn the trim control for
the left channel completely counter-clockwise. Next, slowly turn Speaker
Output A's passive control clockwise. You should begin hearing the test
tone playing through your primary speakers. Increase the level until the SPL
meter reads 85 dB. In most cases, you should not reach 85 dB SPL yet.
8. Begin slowly increasing the input sensitivity (volume) of your primary monitoring
system's left speaker until the acoustic level of the test tone reaches 85 dB SPL.
9. Repeat steps 4 to 8 for the right channel.
Calibration
Calibrating Speaker Levels
3
3.3
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