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This installment of Foundations of Audio explains one of the most essential ingredients in audio mixing, reverb—the time it takes for sound to bounce, echo, and decay during a live performance or recording. Reverb gives a natural richness to your recordings, which is possible to reproduce. Producer and audio engineer Alex U. Case covers the acoustic, mechanical, and digital means for creating reverb, and charts the parameters (room size, density, etc.) you'll need to know to take advantage of the original recording space and enhance it in post. He then shows how to simulate reverb digitally with effects, adding timbre, texture, and contrast, and improve the sound of your mixes with a sense of space and depth.
These techniques can be practiced with the free Get in the Mix sessions, currently available for Pro Tools and Logic Pro.
There's a long list of essential parameters that you'll find on most reverbs. Reverb Time, Pre-Delay, Wet/Dry Mix, these are universal. Most reverbs then offer some form of frequency-based adjustability to the reverb, and there are a handful of other parameters found only on certain mix and models of reverb, such as density, diffusion, and room size. These parameters must be understood before we can take on the high-level musical and technical challenge of making reverbs an asset in our mix.
Top of the list is reverb Time. Reverb Time describes the duration of the wash of reverberant energy. The industry standard is to use something called RT60. RT60 measures the amount of time it takes for the reverb to decay by 60 dB. Let's compare a couple of Reverb Time settings using this snare drum sound. (music playing) First, let's hear a long Reverb Time like 2.5 seconds.
(music playing) With the Reverb Time of 2.5 seconds, it takes about 2.5 seconds for the snare sound to decay to silence. Now we will shorten the Reverb Time from 2.5 to one second. (music playing) Clearly the reverb doesn't last as long, the Reverb Time is shorter. This is one of the most fundamental, defining characteristics that you'll have to specify when you use reverb. To my ear, the first example seems to have too much reverb for most music that I can think of.
But was that short reverb enough? We will forever be trying to balance too much reverb versus too little reverb, and it's not easy to solve. If you want more reverb, do you lengthen the Reverb Time or do you simply raise the faders and make the reverb louder? If you want less reverb, do you achieve that by shortening the Reverb Time or turning down the faders? It seems so simple at first, but you will find even this simple question, how much reverb, is tricky to get right. Expect at first to navigate a steep learning curve, allow yourself to make some mistakes with too much reverb here, not enough reverb there.
We learn from these mistakes when we listen carefully to our mix the next day, undistracted by the DAW. Eventually I assure you, you'll get it all under control. Moving on to the next parameter, we have Pre-Delay. Pre-Delay is that gap in time between the direct sound and the onset of the reverb tail. You can specify a Pre-Delay as short as zero milliseconds, which will effectively make the reverb tail happen as soon as the sound begins, or you can stretch it out to 10, 20, or 30 milliseconds, which is more typical of a real space like a concert hall.
Or you can lengthen it further still up to 50, 100, or 200 milliseconds or more to create an unusual dramatic reverberation effect. See if you can hear the effect as I take the Pre-Delay on the reverb of this snare from 0, to 20, to 120 milliseconds. (music playing) It's important to note, we haven't changed the Reverb Time at all in this example, only the Pre-Delay, only that brief window in time between when the music happens and the reverb begins.
The sound quality that results is complicated to sort through. In later movies in this course we will do exactly that. We'll learn how reverb adjusted through Pre-Delay can be used to fine-tune the timbre of the snare, to create a more realistic spatial quality around the snare, or to lead to a more theatrical embellishment of the snare. I should make quick mention of the important parameter known as Wet/Dry Mix. We talked a little bit about this earlier in the course. The Wet/Dry Mix is essentially the relative level of the reverb or an output of your processor that's the wet part compared to the direct sound itself, the dry part.
Wet/Dry Mix parameters are provided on reverbs, because sometimes the recording engineer puts the reverb on an insert on an individual track and needs to establish the relative level of reverb versus dry signal in the reverb processor itself, but most of the time we get reverb into our mix using the far more efficient Send/Return Effects Loop. In this case we set the Wet/Dry Mix to 100% wet. We actually mixed the wet reverb with the dry tracks in the mixer, not in the plug-in or processor.
We have faders controlling the dry tracks, and we've separate faders controlling the level of the reverb returning to our mix. As you'll see in the rest of this course, we almost always use Send/Return Effects Loops, so almost always leave the Wet/Dry Mix at 100% wet. reverb Time, Pre-Delay, and Wet/Dry Mix are three essential parameters. We also shape reverb in the frequency domain, we cover that next.
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