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Maybe you are like me, and when you step into a stone cathedral or concrete parking garage, you clap your hands to trigger and savor that wash of sound known as reverberation or reverb. When a sound occurs in a room, we hear the direct sound, plus the sound of the room, which is made up of the reflections of the sound from all the surfaces in that room. We call the combined sound of those many reflections reverb. Let me show you how it works and why we use it. The sound of the room, that reverberant wash of sound is very much made up of the many individual reflections created by the room's architecture.
Those reflections arrive at our ears slightly later than the direct sound, but they merge together to produce a single continuous sound. Essentially, when multiple sounds of similar level are happening within about 20 milliseconds of each other, we can't pick any of them out as individual sounds, instead we hear the combined whole. In Foundations of Audio: Delay and Modulation we demonstrated how long delay times create echo-based effects. The delay time is long enough that we hear the delayed sound as a separate event from the direct sound.
This is not what is happening with reverb. Medium and short delay times are used to create chorus and flanging effects. These effects add several delayed signals into the original signal, creating a single sound with a new sonic quality built on the interaction between the sounds within this tight time window. reverb takes this to a whole another level, presenting our ears with countless delayed reflections arriving one after another with microseconds in between. They unite into a single sound.
The point here is that when our musicians play, they fill the space. They acoustically illuminate every visible surface in the room. (music playing) Sound spreads out as it travels, distributing its energy over a larger and larger area as it propagates. And the energy of the sound wave is gradually absorbed by the air in the room and by the materials in the surfaces that bound that room. The result is that the sound grows fainter and fainter over time.
So in any space we hear the sound, plus reverb, and it's always direct sound first, followed by the reverberant wash of energy as it decays to silence. (music playing)
These techniques can be practiced with the free Get in the Mix sessions, currently available for Pro Tools and Logic Pro.
- What is reverb?
- Understanding how acoustic reverb works in rooms
- Working with the signal flow, effects loops, and available CPU resources
- Understanding core parameters, like reverb time and pre-delay
- Simulating space
- Creating nonlinear reverb
- Building pre-delay effects
- Using reverse reverb
- Using convolution correctly