Extron Electronics DMP 64 User Guide - Manual (Page 95)

About Setting Gain Structure
There are two approaches the system designer can take in setting up gain structure,
depending upon where output volume is to be controlled. The output volume of the
DMP 64 can be controlled by either of the following two gain blocks (see figure 58 on the
previous page):
• Volume (e) and
• Pre-mixer gain (b).
NOTE: While the pre-mixer gain control is not in the output signal chain, it can
be used to control program level independent of mix-point levels.
In the following instructions, setup is described for output volume or pre-mixer gain when
appropriate.
Setting Input Gain
Floating point DSP technology is internally more flexible than fixed point. However, the
input ADCs and output DACs always run as fixed point, so it is important to optimize
the audio by setting the input level as close to 0 dBFS as possible. This maintains the
resolution at 24-bit. Within the DSP it is not critical to maintain audio levels at 0 dBFS in
order to secure the resolution at 24-bit.
Input gain can be set using the intended input source device and typical source material
for the installation. When source material is not available, it can be set using pink noise
obtained either from a pre-recorded track on a DVD or CD, or a signal generator.
For program material, set the input gain level (see figure 58, a) so the meters reach
–15 to –12 dBFS, with peaks at approximately – 5 to – 3 dBFS. This setting provides
enough headroom to accommodate transients or unanticipated loud events in the
program material to avoid clipping.
When using pink noise, it should be recorded at – 20 dBFS. If the player has an output
level setting control, set the output of the player to its maximum, or 0 dB of attenuation.
NOTE: If the maximum output setting provides gain, back the control down slightly
from the maximum setting.
When using a signal generator, set the output at –10 dBu.
Whichever pink noise source is used, set the input gain in the DSP Configurator so the
input meter reads – 20 dBFS.
Setting a Nominal Output Level
In order to set up a gain structure to include signal processing, listening to the audio can
be advantageous. Route the audio that carries program material from the source to the
speakers in the room being set up. With the output volume control (see figure 58, e) set
to – 20 dB, set the external amplifier so the source material plays at a volume level that is
reasonably loud, but tolerable.
NOTE: When using the volume control for this purpose, set post-mixer trim (d) to
0 dB. If using the post-mixer trim for this purpose, set volume to 0 dB (100%).
Verify the amplifier is not clipping by observing the amplifier clip indicator. This sets the
amplification (volume) nominal level of the system, and if desired, allows listening while
making adjustments. Adjust or mute the volume control as necessary (see
Setting
Volume Control for the Amplifier Stage on page 91).
DMP 64 • Software Control 89