Extron electronic DMP 64 manual About Setting Gain Structure, Setting Input Gain

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