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Optimizing Audio Levels
The DMP128 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 meters in the DSP Configurator indicate clipping at a user-definable point, with
the default setting at –1dB. This means the meter indicates clipping when it reaches
–1dBFS, or 1dB below actual clipping (0dBFS). 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” may 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 the DSP Configurator are peak-type meters, referenced to full scale, or
0dBFS. For the DMP128 outputs, 0dBFS corresponds to +21dBu, the maximum
output level of the device. Maximum input level is +24dBu. Gain from – 3dB to +80dB
is applied in the analog domain, while attenuation from – 3dB to –18dB is applied in the
digital domain. The input meters are post-ADC, while the output meters are pre-DAC.
DMP128 • Software Control 101