3.
Advanced Calibration —
The calibration box provides a value that corresponds to
the position of the compensation adjustment slider. The SPL box displays the summed
value of the slider and the preceding trim control.
Calibrating Loudness
The user may fine-tune the amount of loudness compensation using the compensation
adjustment slider and adjusting "by ear," or by measuring SPL levels in a particular room,
then using the slider to adjust the loudness filter relative to the SPL of the room and
system gain structure.
Before calibrating loudness, set up the system gain structure (see
Optimizing Audio
Levels
). A pre-recorded track of pink noise or pink noise from a signal generator is
preferable for this purpose. Program material may also be used (using familiar material is
recommended).
If using a signal generator set it to output −10 dBu, then set the input gain of the
DSP Configurator so the input meter reads −20 dBFS. If using a recorded source the pink
noise should be recorded at −20 dBFS and the player output level setting control set to
maximum, or 0 dB of attenuation. For program material, set the input level to meter at
approximately −15 dBFS, with peaks safely below 0 dBFS.
Unmute the mix-point from the pink noise source to the output connected to the room
amplifier being calibrated. With the basic gain structure previously set up, loudness can
be calibrated using an SPL meter or by ear. (Loudness can also be set using an SPL meter,
then fine-tuned by ear.)
To calibrate loudness, use a sound pressure level meter set to “C” weighting:
1.
Set the Loudness processor to
Bypass
.
2.
Place the meter in an average (but somewhat prominent) listening location.
3.
Generate pink noise, or start the program material playback.
4.
Measure the SPL in the room.
5.
In the loudness dialog, adjust the slider until the value in the “SPL” readout box
matches the reading on the SPL meter.
Theoretically, calibration can be performed with the output channel volume and/or
post-mixer gain level set to any comfortable listening level. But a relatively loud volume
(well above the ambient noise in the room) that can be easily measured is preferred.
Loudness is now calibrated. Disengage
Bypass
to hear the compensation.
An alternate method is, with the compensation adjustment slider in its default center
position and the output channel volume fader at 0 dB (100% volume), adjust the amplifier
until the SPL meter reads 90 dB. Loudness is now calibrated. This method works if 90 dB
is an acceptable amplifier/volume limit for the room.
DMP 64 • Operation
46
Summary of Contents for DMP 64
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