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Chapter 9 |
46
Advanced Processing Controls
Audio High Pass Filter Cutoff Frequency
The
High Pass Filter control
(A) sets the cutoff frequency for the high pass filter applied to the input signal. No audio below
this frequency will make it through to the APTO processing engine. In most cases, this control should be set to “Off”, but in
some instances, it may be beneficial to filter out any sub-audible frequencies (below 20Hz).
Voiced-based content with no low frequency information can benefit from a higher setting (60Hz, for example). Delivery
platforms with limited headroom (such as in-flight entertainment or mobile streaming) and consumer devices with small
speakers (mobile phones, tablets, or earbuds) can also benefit from a higher setting to prevent distortion.
Average Hold Threshold
When the Average Hold control (found in the APTO basic menu) is enabled, the Average Hold Threshold control (B)
determines the point at which the hold is triggered in the Compliance processing stage to prevent increasing noise or
background audio.
The value at which the control is set is relative to the Target level . For example, if the Target level is set to -23dB LUFS and the
desired level at which the hold engages in the Compliance processing stage is -34dB, then the Average Hold Threshold should
be set to -10dB
Minimum Speech Duration
Proper dialog-based loudness processing requires the accurate detection and measurement of speech. When
Dialog
Normalization
is enabled, the
Minimum Speech Duration
control (C) determines how many seconds of continuous speech
are required for the measurements to be considered reliable and valid, and after which the Compliance processing stage
adaptively switches to dialog normalization mode.
A minimum of 5 seconds is recommended. Shorter values may incorrectly factor in non-dialog material, and significantly
longer values may cause unnecessary delays in engaging dialog normalization processing, especially in content with shorter
segments of continuous dialog.
Dialog Compliance Measurements
The Dialog Compliance Measurements control (I) determines how many speech measurements are used to perform dialog
normalization in the Compliance stage of processing. Because the algorithm samples the measurements at 0.5 second (one
half of one second) intervals, this control should be set to a time value that is twice the desired average. For example, to base
normalization on a 60 second average, the control should be set to a value of 120.
Note:
The Dialog Compliance Measurements setting only applies to profiles that use Dialog Normalization.
Profiles that do not use Dialog Normalization rely upon the settings of Compliance Window control to
determine their time window.
Adaptive Input Percentage
When the Adaptive Input Detection control (located in the Basic section) is enabled, the Dynamic Range processing section of
APTO dynamically adapts the amount 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 (K) is
determined by the Adaptive Input Percentage control (H).
The recommended setting to start is 50% in order to keep the effect of adaptation more consistent.