Sonnox Oxford Limiter User Manual
Page 32
11.2 SAFE MODE in Combination with Dithering
11 ADDITIONAL INFORMATION FOR PRO TOOLS AAX NATIVE/DSP
11.2 SAFE MODE in Combination with Dithering
SAFE MODE allows the use of slower attack times in the Limiter section (often
considered more musical) coupled with the use of a time-constant controlled inflator
section to catch any over- range peaks and transform them to legal sample values while
still retaining the apparent loudness of the original over-range peak.
SAFE MODE uses an inflation algorithm that cannot generate an over-range value, but
can generate a digital maximum value that may be interpreted as a clip. Once dither is
added, the result can most definitely be over-range, and then hard clipped in the
dithering/truncation section. The AAX Oxford Limiter applies the minimum possible gain
reduction to ensure that when Safe mode is on, regardless of whether dithering is enabled
or not, the Oxford Limiter cannot clip and the clip lights do not activate.
11.3 Reconstruction Meter and Auto Compensation of Inter-Sample
Peaks
The AAX Oxford Limiter features two reconstruction meter modes:
DAC Simulation –
which was present in the RTAS/TDM version – and a new
True Peak mode, selected by
pressing the Sonnox button on the plug-in interface.
DAC Simulation is selected by default, ensuring that previous RTAS/TDM sessions will
sound the same on first load. However, True Peak mode can be selected instead which
will then be saved with the session.
When using
DAC Simulation mode, bear in mind that a signal that is already 2dB over
unity when it hits the Auto-Compensation section will remain 2dB over unity. It is only
inter- sample-peaks that are corrected, not sample-peaks. In this mode, the Auto-Comp
feature should be understood as a feature that ‘Corrects for illegal sequences of legal
sample values’, and not ‘corrects illegal sample values’. As the Recon Meter in DAC
Simulation mode will not work correctly unless the samples are already limited to digital
maximum, this means using Safe Mode, have 16-bit or 24-bit dither enabled or lower the
input or output fader.
In
True Peak mode, the true inter-sample peak value of any sample sequence is
calculated. This means that if you use slower attack times and do not use Safe Mode, the
Auto-Comp section when enabled will now catch and compress any over-range peaks
escaping the main Limiter section. For this specific case, this gives a different sound to
the hard clipping that occurs in the DAC Simulation (RTAS-TDM) version.