Calibration - BLUE SKY BMC MK III User Manual

The following system calibration instructions are for a bass-managed
speaker system, such as Blue Sky's ProDesk, Sky System One, SAT
265, SAT 8, SUB 212, or Big Blue system.
There are three steps to the calibration procedure:
1 - Setting the electrical / digital signal level
2 - Setting the reference level (REF)
3 - Setting the acoustic playback level
The instructions included within this manual detail two separate
ways to do step 3. One method uses bandwidth limited test files and
requires only a SPL meter. The other method uses full-bandwidth
pink noise and requires the use of a 1/3 octave real time analyser
(RTA), along with a SPL meter.
Before starting the calibration procedure you will need to download
BlueSkyTestFiles.zip (18MB file) by going to www.abluesky.com. To download
the test file, "Right Click" the file, select "Save Target As" and the file will
begin downloading. Once downloaded, un-zip the test files and either burn
the test files to a CD or import them into your DAW.
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 (etc.), not both channels at the
same time. If you are using a CD player as your source, use only one
channel of the CD player. 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.
THEORY
The purpose of calibration is to adjust the overall electroacoustic 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
using broadband pink noise.
*Also, please note that the LFE channel gain in a 5.1 system varies
from 0dB to +10dB, depending on the encoding format that is being
used. Since typically the LFE channel is not calibrated as a separate
entity, the LFE gain will not impact system calibration. For more
information about the LFE channel refer to page 15 [Additional Surround
and Setup Information].
Page 12 • User Manual • 5.1 System Calibration
BMC MK III
USER MANUAL • 11 • 5.1 SYSTEM CALIBRATION
SETTING THE ELECTRICAL / DIGITAL SIGNAL LEVEL
Step 1
Step 2
Step 3
Step 4
Step 5
The common calibration levels
L C
Movie Theatrical release 85dB 85dB
Movie DVD release 85dB 85dB
Broadcast / 85dBc or 78dB 78dB
Music (Stereo) 85dB
Music ( 5.1) 85dB 85dB
TURN OFF THE MONITORING SYSTEM
Select a preset that uses bass-management, or make sure that
bass-management is turned on (set to YES) within the current
preset, by going to the SETUP menu. Use the "+" (R) and "-" (L)
buttons to toggle between yes and no. See image below:
BASS MANAGE MAIN
YES
Now press the MENU button 2 times, or until the display reads
"CAL CHANNELS". See image below:
CAL CHANNELS
PUSH UP/DOWN/RTN
Press the DOWN (LFE) arrow button once, or until the display
reads "SUB OFFSET MAIN" and then use the "-" button to set
the offset to -10dB. This setting will give the subwoofer / LFE
summation buss the greatest amount of electrical headroom. If
you are not feeding the BMC a +4dBu nominal signal or if it turns
out that your subwoofer doesn't have enough electrical gain to
get the desired output, then you should leave the offset in the
0dB position. See image below:
SUB OFFSET MAIN
GAIN = -10.0 dB
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
that the output meter reads -20dBFS. If you are using an analog
console, set the output level to 0dB VU. Then hard pan the signal
to the center channel output and repeat for the center channel
(then repeat for the each of the remaining channels). Once
calibrated do not move the output faders.
Mute the BMC and make sure the 1kHz tone is OFF .
R LS RS SUB*
85dB 82dB 82dB 85dB
85dB 85dB 85dB 85dB
78dB 78dB 78dB 78dB
85dB 85dB
85dB 85dB 85dB 85dB