Extron Electronics DMP 64 User Guide - Manual (Page 94)

Optimizing Audio Levels
The DMP 64 uses floating point DSP technology, processing data using a combination
of 32- and 64-bit algorithms. The analog to digital converters (ADC) and digital to analog
converters (DAC) sample at 48 kHz with 24-bit resolution.
With floating point DSP it is extremely difficult to clip the audio signal within the DSP audio
signal chain, after the ADC input and before the DAC output. That means the audio signal
must not be clipped at the input ADC. Clipping gives audibly undesirable results and once
the audio is clipped at the input there is no way to correct it further down the signal chain.
If audio clipping occurs at the output DAC that is not a result of clipping at the input ADC,
there are ways to address it within the DSP audio signal chain.
The meters in the DSP Configurator indicate clipping at a user-definable point,
with the default setting at –1 dB. This means the meter indicates clipping when it
reaches –1 dBFS, or 1 dB below actual clipping (0 dBFS). Setting the clipping meter
below clipping provides a “safety net”, allowing the user to reduce input gain before
clipping actually occurs. This safety net can be increased or decreased by selecting
Tools>Options>Processor Defaults>Defaults>Meter Clipping , and setting the
Clip Threshold to a number between 0 (dB) and – 20 (dB).
NOTE: When the Clip Threshold is set to 0 (dB), clipping is indicated only when
clipping occurs.
Meters within the DSP Configurator are peak-type meters, referenced to full scale, or
0 dBFS. For the DMP 64 outputs, 0 dBFS corresponds to +21 dBu, the maximum output
level of the device. Maximum input level is +24 dBu. Gain from – 3 dB to +80 dB is applied
in the analog domain, while attenuation from – 3 dB to –18 dB is applied in the digital
domain. The input meters are post-ADC, while the output meters are pre-DAC.
The remainder of this section will reference the gain, trim and volume controls outlined in
figure 58 below.
a c d e b
Figure 58. Gain, Trim and Volume Controls
a Mic/Line input gain d Post-mixer trim
b Pre-mixer gain e Output volume
c Mix-point gain
DMP 64 • Software Control 88