Many of us are probably familiar to the concept of HDR (High Dynamic Range) in photography: a process that “attempts to maintain local contrast, while decreasing global contrast”, right? But, what about HDR in audio.
Well, yes, it exists, and it’s pretty useful (specially for games). I got to know it because of an article, called “Finding Your Way With High Dynamic Range Audio In Wwise” that describes the concept and talks about it’s implementation in WWise (because the original post was written in 2013, maybe something technical have changed inside the middleware).
Well, paraphrasing the article, HDR audio works in your mix “by making soft sounds inaudible when loud sounds play, and making them audible again when playing alone. The relative levels of sounds between one another in the HDR world are preserved, creating the illusion of a greater dynamic range, particularly effective with impact sounds, while in fact they are compressed within the output device’s lower dynamic range.”
Here is a picture that can make us understand this better.
As you can see, as a sound triggers the HDR bus threshold, it maintains the available dynamic range by making inaudible soft sounds (that wouldn’t be heard anyway, because of the much louder sounds). Pretty cool, right?!
It is a similar process to ducking a sound with a compressor, using side-chains. The difference is that it doesn’t compresses the soft sound, it just makes it inaudible by bringing the “window bottom” up (as seen in the graphic above). It is a slight different way, that makes a big difference on the final result.
And why is this really useful?! Well, as the article states:
HDR, as a dynamic range compressor, has many benefits, and one of them is to add clarity to a mix. In the following example, a loud machine gun sound is fired repeatedly. It takes the entire place; there is no need to leave anything else behind. The figure shows that its presence effectively ducks down the volume of other presumably ambient or less important sounds. This helps us focus on what is important at this point in the game by removing unnecessary noise. This can also be accomplished using side-chaining, because one sound is clearly more important than the other with regards to gameplay.
Another potentially beneficial aspect of HDR is that it can help you control loudness between various elements of the audio scene. For example, say you have two distinct sounds constituting an ambience, and the amplitude of one of them varies greatly. Whenever a sound goes above the HDR threshold, a portion of its energy is spent ducking down the other ambient sound instead of just piling up. The relative level between them is maintained, so perceptually the louder sound will effectively be louder than the other, but the overall level of the ambience mixture remains around the desired target level. This way, ambiences remain ambiences and do not interfere with other elements of the scene. HDR achieves this task more elegantly than side-chaining because the relative importance of both sounds is not known a priori. The system figures it out based on their respective instantaneous loudness.
So HDR is a really nice help to make our mixes sound better and more clear, and also to have more control over the overall sound of the game. I’m really interested in understanding more about this, so if anyone has anything to add or share, please do! It would be a major help for me and the readers of the blog.
Mauricio Ruiz – www.mauricioruiz.me