Dolby Laboratories DP570 - Manual (Page 81)

Configuring a Monitor System Calibrating Speaker Playback Levels
Dolby ® DP570 Multichannel Audio Tool User’s Manual 69
A.3.7 Measuring SPL
To accurately measure SPL:
1. Sit in the reference listening position. Set the SPL meter to C weighting and Slow
response.
2. Facing the front speakers, hold the SPL meter at chest level, with the microphone
facing up at an angle of approximately 45 degrees to the Center speaker. Keep the
meter at arm’s length to prevent measuring audio that may reflect from your body.
3. Keep the SPL meter in this position. Make sure that the meter is aimed at the Center
speaker as you take readings for the Left and Right speakers.
4. To take the SPL readings for the Left Surround or Right Surround speakers, keep the
meter at the same angle and position as you did for the front speakers. Turn your
body 90 degrees from the Center speaker toward the wall closest to the Surround
speaker you are measuring. This minimizes shadowing (obscuring the meter with
your body).
A.3.8 Computing Channel Trims
After measuring each speaker, compute the difference between the measured actual SPL
and the target SPL. Adjust the trim for each speaker appropriately using the Multichannel
Trims controls shown in Figure A‐8.
Figure A-8 Multichannel Trims Controls
When you have set trim levels for all your speakers, click the test noise control shown in
Figure A‐2 directly under the Analog Outputs check box.
A.3.9 Subwoofer Calibration
Subwoofers are calibrated using a different process than the rest of the speakers, preferably
with different equipment. To properly calibrate the subwoofer, a real‐time analyzer (RTA)
is required. If an RTA is not available, you can approximate the settings with an SPL meter.
When using an RTA, proper calibration requires setting the LFE channel signal sent to the
subwoofer, within its typical bandwidth of 25 to 120 Hz, 10 dB higher than the main
channels. Figure A‐9 shows a sample RTA display of a properly calibrated subwoofer.