Basic APTO Processing
Choosing an APTO Profile
In most cases, ARC is truly a “set and forget” processor and simply choosing a factory profile is all that is required.
To select a profile, navigate to the Program 1 (or Program 2) menu (A), click the Load button in the APTO Loudness Control section (B), mouse over Factory Presets (C), then choose an appropriate profile from the Factory Preset List (D).
Basic APTO Controls
The individual controls within each APTO factory profile have been adjusted in such a way that they automatically deliver the required result associated with the profile name (such as “EBU R128 Adaptive”). However, there may be situations in which you want to adjust certain individual parameters to customize or fine-tune the audio.
The APTO Loudness Control section of the Program 1 and Program 2 menu contains the basic controls for each program path and are identical in terms of controls and functionality, though completely independent of one another in their operation.
Figure 8-2 – Basic APTO controls
Current Profile
The currently selected profile is displayed in the Profile window (A).
Note: In the current version of ARC, there is no indication that the factory profile has been modified as a result of changing the values or settings of individual controls. This feature will be included in an upcoming software upgrade. In the meantime, we strongly recommend that you save any changes and create uniquely-named user profiles as you make adjustments as outlined below in the paragraph on using the “Load and Save” buttons.
Load and Save
The Load button (B) is used to recall factory profiles, user profiles, or to import a profile previously saved to your computer. Any changes or modifications to the current profile can be saved by using the cryptically-named Save button (C).
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 (D). This is useful for a quick comparison between the unprocessed and processed audio. When bypass is engaged, the button will turn red.
Reset
Clicking on the Reset button (E) 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.
Target Loudness
The Target Loudness control (H) sets the desired average loudness level of the output signal in either LUFS or LKFS, depending upon the profile. Some profiles, such as EBU R128, will measure loudness according to overall program levels while others, such as ATSC A/85, will do so based on dialog and gated speech measurements.
To change the target loudness value, click in the Target Loudness field, type in the desired value, and click on the green checkmark to save your change (or the red “X” to exit without saving).
Adaptation
The Adaptation control (G) determines how much processing is applied to the incoming signal in the Dynamic Range processing stage, and, in combination with various individual controls, determines the dynamic range of the output audio.
The ideal amount of Adaptation depends upon both the source content and the destination platform. Content that has been pre-analyzed for loudness, scaled, and normalized in the file domain will require less realtime processing than, say, live sports, which can have rather unpredictable audio levels. Programming streamed to a mobile device or expected to be heard on lower quality earbuds will benefit from more Adaptation than the same content destined for a home cinema presentation.
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.
Maximum True Peak Limiter and Limiter Threshold
The True Peak Limiter control (J) enables and disables the True Peak Limiter, which is the final processing stage just ahead of the final output. The Maximum True Peak value (F) 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.
Dialog Normalization
The Dialog Normalization control (L) enables dialog detection and measurement. When enabled, APTO’s Compliance processing stage uses long-term speech-only measurements rather than the overall input program loudness to ensure the output target level is achieved.
The use of dialog-based measurement is normally determined by regional regulations. For example, ATSC A/85 relies upon anchor-based normalization, specifically dialog, while EBU R128 recommends the use of overall measurements. This is reflected in their respective factory profiles.
Average Hold
When the Average Hold control (K) is enabled and the output audio of the Dynamic Range processing stage falls below the level set in the Average Hold Threshold control (located in the Advanced menu), APTO’s Compliance stage of processing becomes inactive until the level once again rises above the threshold. This helps prevent noise and low-level background audio from being increased unnecessarily.
Adaptive Input Detection
When enabled, the Adaptive Input Detection control (I) 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 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 to the actual incoming content.
If the incoming content has already been analyzed and loudness-corrected in the file domain, less overall processing is required and a more natural-sounding output can be achieved by setting the Average Input Level (located in the Advanced menu) 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.
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