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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 0dBFS as possible. This will maintain the
resolution at 24-bit. Within the DSP it is not critical to maintain audio levels at 0dBFS in
order to secure the resolution at 24-bit.
Input gain can be set using the intended input source device and typical source material.
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 level (
a
) so the meters reach approximately
– 15to– 12dBFS, with peaks at approximately – 5 to – 3dBFS. This setting provides
enough headroom to accommodate transients or unanticipated loud events in the
program material to avoid possible clipping.
When using pink noise, it should be recorded at – 20dBFS. If the player has an output
level setting control, set the output of the player to its maximum, or 0dB of attenuation.
If the maximum output setting provides gain, then back off slightly from the maximum
setting. When using a signal generator, set the output at –10dBu. Whichever pink noise
source is used, set the input gain in the DSPConfigurator so the input meter reads
– 20dBFS.
Setting a Nominal Output Level
In order to set up a gain structure to include signal processing, listening to the audio may
be advantageous. Route the audio that will carry program material from the source to the
speakers in the room being set up. With the output volume control (
e
) set to – 20dB, 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
0dB. If using the post-mixer trim for this purpose, set volume to 0dB (100%).
Verify the amplifier is not clipping by observing the amplifier clip indicator. This will set
the amplification/volume nominal level of the system, and if desired, allow listening while
making adjustments. Adjust or mute the volume control as necessary
(see “Setting Volume Control for the Amplifier Stage” on page105).
DMP128 • Software Control 103