Expanded Calibration Guide - BLUE SKY EXO User Manual

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.
Stereo Monitoring System
USER MANUAL • 8 • Expanded Calibration Guide
User Manual • Expanded Calibration Guide • Page 9
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 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.
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
GAIN control for 85 dBc. Then mark the monitor level as
your reference position.
B. The other method is to set eXo 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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