Stereo Monitoring System
USER MANUAL • 8 • Expanded Calibration Guide
User Manual • Expanded Calibration Guide • Page 9
Instructions for electroacoustic calibration of a 2.1 audio system
using a SPL meter and Blue Sky’s test files.
Before starting this procedure you will need to download BlueSkyTestFiles.
zip (an 15 MB zip file) by going to:
www.abluesky.com
Once downloaded, either burn the test files to a CD or import them into your
DAW and follow the instructions below.
ADDITIONAL REQUIRED ITEMS
1. 2.1 Monitoring System
2. SPL Meter - such as those sold by (RadioShack)
BlueSkyTestFiles.zip Includes 4 files:
•
1000Hz SINEWAVE -20dBFS.wav – a 1kHz file recorded at -
20dBFS for electrical calibration
•
40-80Hz PINK NOISE -20dBFS.wav – a 40Hz to 80Hz bandwidth
limited pink-noise file recorded at -20dBFS
•
500-2.5kHz PINK NOISE -20dBFS.wav – a 500Hz to 2.5Hz
bandwidth limited pink-noise file recorded at 20dBFS
•
Pink Noise full bw -20dBFS.wav – a full-bandwidth pink-noise file
recorded at - 20dBFS
These test files are all mono files. Please make sure you hard assign them
to the left and then the right, not both channels at the same time. If you are
using a CD player use only one channel of the CD player.
THEORY
The purpose of calibration is to adjust the overall electroacoustics system
gain so that 0dBVU of electrical signal level equals a certain acoustic level
at the listening position. Since most recording media is now digital, the
reference electrical signal level is usually –20dBFS with 20dB of headroom.
The reference SPL level however can vary based on the delivery media and
speaker type.
Please note that the bandwidth limited signals that have been provided, limit
many of the room interaction affects often associated with measuring SPL
and broadband pink noise.
All test signals are recorded at –20dBFS including the 1 kHz sine wave tone.
The sine wave tone is used to set the electrical output level throughout the
signal path, right up to the point you get to the speakers, while the various
pink noise signals are used for acoustic measurements and calibration.
The following procedure assumes you are calibrating the system to 85dBc
SPL.
Step 1 TURN OFF THE MONITORING SYSTEM (until step 4)
Step 2 Remove all eq and dynamics from the signal path and set all
controls to zero / unity gain. Play the 1kHz Sine Wave, hard
assign it to the left channel only, and adjust the output fader
so the output meter reads -20dBFS. If you are using an analog
console, set the output level to 0 VU. Then hard pan the signal to
the right channel output and repeat for the right channel. Once
calibrated do not move the output faders.
Step 3
Mute everything and make sure the 1kHz tone is OFF .
Step 4
Now that the system has been electrically calibrated
turn ON the eXo
2
Stereo Monitoring System.
Step 5 Assign the 500-2.5kHz pink noise signal to the left channel
or right channel only. Make sure there is nothing coming from
the right channel (or any other channels). Because this signal
is bandwidth limited, you don’t have to worry about turning the
subwoofer (SUB) off. There are two methods of setting the
levels.
A. If you have a master monitor level control, you can set the
sat gain control at reference and then adjust the eXo
2
GAIN
control for 85 dBc. Then mark the monitor level as your reference
position.
B. The other method is to set eXo
2
master GAIN control to the
position you want as a reference level and then use your own
volume controls to set 85 dBc. If you use this method you should
mark the knob position with a grease pencil so you can always go
back to reference level if the knob gets moved.
For either method:
SPL should be measured at the mix position, with the SPL meter
at arms length, with the microphone at seated ear height, angled
at approximately 45 degrees, and pointed at the center point
between the left and right speakers. Once the left channel is set
to 85dBc, repeat this step for the right channel
Step 6
Feed 40-80Hz pink noise signal to the left channel only. Adjust
the subwoofer level
control (SUB) until the subwoofer measures
85dBc (slow) at the mix position. The meter will bounce around
a little, so you will need to do a mental average (
I tend to filter
out the peaks in my mind, so I don’t set the SUB too hot
). The
right channel should measure about the same and no additional
adjustments need to be made.
Step 7
You can play the full-bandwidth pink noise, assigning it to the left
and then the right channel (not at the same time). You should
measure about 85dBc. It may be a little higher, because below
30Hz the room may have a little extra gain. No adjustments
should be made with Full Bandwidth pink noise, unless you have
an RTA (real time analyzer).
Step 8 You are finished and the calibration process has been completed
– enjoy!
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