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APTO™ Processing
Ideally, you want enough Adaptation to achieve compliance and keep levels within the viewer's comfort zone
and at a stable average level, but not so much that the audio sounds unnatural or over-processed. APTO is based
on a psychoacoustic model that takes into account human hearing and perceived loudness and remains very
natural-sounding even when extensive processing is applied, but it is generally advisable to keep the amount of
Adaptation under 50% when possible. If incoming content is so poorly controlled as to require higher values, it may
be necessary to adjust some of the individual controls and create a custom profile to address this scenario.
Bypass
APTO can be bypassed so that the input audio is passed through to the output without being processed by clicking
on the Bypass control (10-1C). This is useful for a quick comparison between the unprocessed and processed
audio.
Reset
Clicking on the Reset button (10-1D) resets the loudness measurements as well as the gain buffers APTO uses in
the normalization stage. Resetting at the start of each individual program element provides accurate per-segment
loudness measurements, aids in achieving overall compliance, and ensures that adaptive processing decisions are
made based upon the current program dynamics. A GPIO input may be used to trigger the reset automatically.
Maximum True Peak Limiter and Limiter Threshold
The True Peak Limiter control (10-1E) enables and disables the True Peak Limiter, which is the final processing
stage just ahead of the final output. The Maximum True Peak value (10-1F) sets the level beyond which the
True Peak limiter engages and attenuates the processed audio so as not to exceed the set level. These controls
comply with the True Peak measurement as outlined in ITU-R BS.177-4 Annex 2.
Adaptive Input Detection
When enabled, the Adaptive Input Detection control (10-1G) dynamically adapts the amount of processing
occurring in the Dynamic Range stage of processing depending upon the actual measured average level at the
input. The degree to which the actual input levels influence the processing versus relying upon the value of the
Average Input Level control (found in the Advanced menu) is determined by the Adaptive Input Percentage
control (also located in the Advanced menu).
When Adaptive Input Detection is disabled, Dynamic Range processing decisions are made based strictly upon
the value set in the Average Input Level (found in the Advanced menu) and in accordance with the settings of
other parameters and controls.
Adaptive Input Detection is especially useful when source audio levels are unknown or are likely to vary widely
as it allows the Dynamic Range processing stage to respond more predictively the actual incoming content.
If the incoming content has already been analyzed and loudness-corrected in the file domain, less overall pro-
cessing is required and a more natural-sounding output can be achieved by setting the Average Input Level to
the same value as the target level used during file-based correction and reducing the value of the Adaptive Input
Percentage control (also found in the Advanced menu) or disabling Adaptive Input Detection altogether.
Chapter 10 | 57
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