Understanding Undo

Undo is a signature feature of all Omnia.9-based processors, including Enterprise 9s, that combines two separate and independent processing stages: Declipping and multiband expansion.

In this unique hybrid approach, the de-clipper intelligently recreates missing audio peaks that were clipped in the mastering process, while the multiband expanders add dynamic range to material that has been overly compressed.

These trends in mastering began in the mid-1990s and were in full swing by the early 2000s. Though some recent recordings are starting to show signs of bringing some dynamic range back to recordings, these practices are still commonplace, and Undo remains an antidote for this condition.

Each Station in a given Omnia Enterprise 9s installation has one instance of Undo that can be applied to its input audio source. The output of the Undo process is common to all processed output paths (FM, HD, and Streaming) in that Station.

Undo Presets

Much like the audio processing controls and settings, Undo utilizes the concept of factory and user presets to recall settings. Please see the Working with Presets section for an overview of managing presets.

Note: Though the Undo presets work in the same way as the processing presets, Undo parameters and settings are not part of the audio processing presets. Undo presets are unique files that are separately and independently managed.

Enabling Undo

Select the Undo button (A) for the desired Station, then click on the Undo Main button (B).

• The Power button (C) is the main on/off control for Undo. Turning the power off completely removes both the declipper and multiband expanders from the input audio path and eliminates the option to display any of the multiband expander meters in the UI or observe the effects of Undo using the oscilloscope. Turning the power off lessens overall CPU usage and reduces latency.

• The Bypass button (E) simultaneously turns off both the declipper and multiband expander, but the input audio is still routed through the Undo circuit. In contrast to the Power button, overall CPU usage and latency are not reduced, and the activity of the multiband expanders - if they were enabled - can still be viewed in the UI.

• The declipper can be independently enabled and disabled with the Enable Declipper button (D).

• Likewise, the multiband expanders can be independently enabled and disabled with the Enable Expander button (F).

Note - If it is necessary to use the Undo Power button while on the air, be advised that the change in latency will have an audible effect. Turning Undo off will cause the audio to skip ahead slightly, resulting in an audible "jump", while turning Undo on will introduce a short but audible gap. Using the Undo Bypass button avoids this and is recommended for instances that are currently on the air.

Declipper

Select the Undo button (A) for the desired Station, then click on the Declipper button (B). The Declip Level slider (C) adjusts the level of amount of declipping, with a setting of 5 representing a normal level suitable for the vast majority of affected recordings. Since the declipper has no audible effect on source material that doesn't require repair, it can safely be set to whatever level works best on the "worst case scenario" content.

Multiband Expander

For the vast majority of users, choosing one of the factory Undo presets will be sufficient to achieve the desired results. Because of the complicated nature of the multiband expanders, we generally advise against making any changes to the controls in the six expander-specific menus unless you have a very specific reason to do so, and have a firm understanding of how the controls work.

Density Detector Band Weighting

Each band of the expander has a corresponding density detector. The controls in the Density Detector Band Weighting menu (A) allow you to determine how much control each detector provides its own band as well as any other expander band.

To put this concept into traditional processing terms, it is similar to “band coupling” in a multiband compressor, where all bands may operate completely independently of one another or may influence one another by way of coupling to varying degrees.

The degree to which each dynamics detector band influences and controls each expander band is determined by a 5 x 5 slider matrix. Each column (B) represents a dynamics detector band, while each row (C) represents an expander band.

The default (and recommended) settings are set up so that each expander band is controlled almost entirely by its corresponding dynamics detector band but with some control provided by surrounding dynamics detector bands. Higher values mean a particular dynamics detector band has more influence over a particular expander band and vice versa.

Note - In order to provide a method for one dynamics detector band to provide 100% of the control over a single expander band, every control must be designed to go all the way to 100. When one control is set to 100 and other controls in that band are set to a value higher than 0, (causing a sum greater than 100), Undo interprets that information and adjusts the settings of each band to maintain proportional influence for each band relative to 100.

Dynamics Detector to Ratio

The sliders in the Dynamics Detector to Ratio menu (A) allow you to set time constants of the expansion ratio adjustment, the Expansion Start levels, and Transition Width levels for each of the 5 bands.

• The Attack (B) and Release (C) controls determine how quickly the expansion ratio will track along with the dynamic detector settings. The default (and recommended) setting is 100, meaning the expansion ratio will track instantaneously with no additional delay.

• When the dynamics detector falls below a certain level, expansion will begin starting at a minimum ratio of 1:1 and increasing to a maximum ratio of 4:1. The point at which that expansion begins is set by the Expansion Start control (D) in each band.

• The relative point at which the expansion reaches its full 4:1 ratio is determined by the Transition Width control (E) in each band.

Peak Detector

Undo measures audio peaks as a means by which to set the expander thresholds based upon the incoming program audio. The controls in the Peak Detector menu (A) adjust the attack and release speed of each band of Undo’s Peak Detectors.

• The Attack speed controls (B) adjust how quickly the expanders reacts to incoming audio peaks. Faster settings will make them more reactive to smaller incoming peaks by raising the threshold, while slower settings will make them less reactive.

• The Release speed controls (C) determine how quickly peak values fall back toward the actual audio levels. Faster times will cause the peak levels to fall more quickly.

Expander Levels

The overall levels of expansion and the relationship between per-band and wideband control are adjustable using the controls in the Expander Levels menu (A).

• The Relative Threshold control (B) for each band determines how far below the currently detected peak the expander threshold sits. Lower thresholds (moving the slider to the right) result in a greater peak-to-threshold distance and therefore provide more expansion. Higher thresholds (moving the slider to the left) narrow the peak-to-threshold distance and provide less expansion.

• In addition to an adjustable per-band peak detector with adjustable attack and release speeds (whose function is described above in the Peak Detector menu section), each channel also has a wideband peak detector with fixed attack and release speeds. The Band<WB Distance Limit controls (C) determine the greatest distance by which an individual band’s peak detector can fall relative to the wideband level and keeps any one band from being expanded if there are insufficient levels to begin with. For example, if the current wideband peak is -6dB and this control is set to -10dB, the peak detector for that individual band will not fall below -16dB.

• The Maximum Gain control (D) sets the absolute maximum amount of gain that can be applied to the audio in each expander band regardless of program material or any other control settings.

Expander Rates

The controls in the Expander Rates menu (A) adjust the attack and release rates of each expander band as well as those of each band's speed governors.

• The Expander Attack speed control (B) determines how quickly each band’s expander will rise when the audio is in need of expansion. Faster settings will expand the audio more quickly.

• The Expander Release speed control (C) adjusts how quickly the expander levels will fall once the expansion is no longer called for. Faster settings will allow the levels to fall more quickly.

A second set of parallel expanders looks at the same input and automatically scales the attack and release characteristics of the main expanders. These Speed Governors detect when the main expanders have been operating at full speed for an extended period of time and will slow down them down as needed.

• The Governor Attack speed control (D) determines how long the speed governors wait before scaling back the speed of main expanders. Faster settings will cause the speed governors to step in and slow down the expanders sooner.

• The Governor Release speed control (E) determines how long the speed governors wait before returning control back to the main expanders. Faster settings will cause the speed governors to relinquish control sooner.

Expander Ratios

Each expander band can operate across a range of ratios between 1:1 and 4:1 as determined by the controls in the Expander Ratios menu (A).

• The Minimum Ratio control (B) sets the lowest ratio each band can use.

• The Maximum Ratio control (C) sets the highest ratio each band can use.