Optimizing Audio Levels - Extron electronics DMP 128 User Manual

Optimizing Audio Levels

The DMP 128 uses floating point DSP technology, processing data using a combination
of 32- and 128-bit algorithms. The analog to digital converters (ADC) and digital to analog
converters (DAC) sample at 48kHz, 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 DSP Configurator meters 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 actual 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 and – 20 (dB).
NOTE: When the Clip Threshold is set to 0 (dB), clipping is indicated only when
clipping occurs.
Meters within DSP Configurator are peak-type meters, referenced to full scale, or 0 dBFS.
For the DMP 128 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.
DMP 128 • Software Control 101