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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.
Convolution brings a major capability to our studio. Any track we record using typical close miking techniques can be sonically transported to sound as if it were recorded in any space in the world. All you need is the impulse response of that space. We use convolution to put our pianos in the finest concert halls in Europe, our drums in the best recording studios in Los Angeles, and our vocals in the most thunderously awesome caves in Africa. But convolution does have limits, so we take a look under the hood in this movie and the next, so that we're better informed users of the technology.
Recall the convolution is done by sending an impulse into the room, a simple single instantaneous spike and recording the resulting pattern of spikes that follows. This pattern of spikes defines the sound of the room. It's called the impulse response, as it is the acoustic response of the room to an impulse signal. The process of convolution applies the room's response to any other signal we feed it. But the process doesn't work for things that change over time. Imagine a room where the walls move. Such spaces are very rare, but it illustrates a critical point.
If the walls move, then the pattern of spikes that make up the impulse response will change too. But convolution only has the ability to apply a fixed impulse response to your audio. So a system that changes simply can't be re-created through convolution. Fair enough, the spaces I care about don't change much. The walls don't move in most symphony halls, cathedrals, and famous reverb chambers. Convolution is great for these spaces. What about springs and plates? They too don't change the resident behavior during the course of a mix, so convolution is a terrific way to bring vintage springs and plates into your productions.
You'll also see convolution use to simulate other algorithmic digital reverbs. This usually doesn't work. The oldest digital reverbs ran simpler static algorithms that can be represented by fixed impulse response. But the high-end algorithmic reverbs since the 90s pretty much always use changing delays within their algorithm. So convolution can't convey the full rich complexity of their sound. To use convolution where appropriate, make sure that the space or device it is stimulating exhibits steady behavior.
It's ideal for reproducing the sounds of springs, plates, and every glorious space you want to hear in your mixes.
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