Since the HDR system works with logical volume values set in Wwise, it is unaware of the actual amplitude of the input sounds, and therefore sees them as black boxes with constant volume throughout the duration of the sound. Most of the time, the amplitude of sounds vary. Imagine an impact sound with a transient and a decaying part. If this sound was loud enough to fix the position of the HDR window, this position will remain unnaturally constant during the whole duration of the sound. See the resulting effect on the window in Figure 29.11, “HDR window with a decaying impact sound without envelope”.
In Wwise, it is possible to let the HDR system peek into the black box by enabling envelope tracking. In the HDR tab of the desired sound's properties, select the Enable Envelope check box: the amplitude envelope of the audio file is then analyzed and is attached to the sound's metadata. At run-time, the HDR system uses this data to move the window appropriately, as can be seen in Figure 29.12, “HDR window with a decaying impact sound with envelope, playing above a softer, steady background sound”.
For the following figure, the input is on the left, the output on the right and the corresponding output wave is below.
Figure 29.12. HDR window with a decaying impact sound with envelope, playing above a softer, steady background sound
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Notice the lull after the impact sound in the first figure above, caused by the HDR system interpreting it as being constant.