Thursday, December 08, 2011
In The Studio: Audio Effects Explained, Part 2 – Reverb
Exploring the different types of reverb, with audio samples, as well as tips for using reverb
Continuing my series on effects, I’m talking about reverb. (See part 1 about modulation here.)
The different types and methods, and I’ll also explain the most important parameters.
I’ll mostly be talking about the kinds you will be using when mixing and what is available as plugins.
Digital Reverb Technology
There are two ways of creating a reverb effect in the digital world, by using mathematical calculations to create a sense of space, which is called algorithmic. And, by creating an impulse response, a snapshot of a real space, and applying that to the sound, which is called convolution.
Reverb is essentially a series of delayed signals, and algorithmic reverbs work pretty well to recreate this. Most reverb plugins, stomp boxes, and racks are algorithmic style.
When you want really realistic reverb, then convolution can not be beat. To create an impulse response the creator goes into a room and records the sound of a starter pistol going off and the natural reverb of the room.
The recordings are then deconvolved in software which is removing the sound of the starter pistol from the recording, leaving only the reverb.
Sine wave sweeps can also be used for the impulse creation. This is a more accurate way of creating reverb because it also captures the character of the room, and the way different frequencies react in the room.
The same process can be used to create impulse responses of speaker cabinets, guitar amps, vintage rack gear or basically anything that can make a sound.
Analog Reverb Types
In the analog world there are a few other ways, most of which will not be available to the home studio musician, except for their recreations in plugins.
Analog reverbs come in three flavors - plate, spring, and chamber.
Invented in 1957 by EMT of Germany, the plate reverb consist of a thin metal plate suspended in a 4-foot by 8-foot sound proofed enclosure. A transducer similar to the voice-coil of a cone loudspeaker is mounted on the plate to cause it to vibrate.
Multiple reflections from the edges of the plate are picked up by two (for stereo) microphone-like transducers. Reverb time is varied by a damping pad which can be pressed against the plate thus absorbing its energy more quickly.
This is what a plate reverb sounds like: platereverb.mp3
A spring reverb system uses a transducer at one end of a spring and a pickup at the other, similar to those used in plate reverbs, to create and capture vibrations within a metal spring. You find these in many guitar amps, but they were also available as stand alone effect boxes. They were a lot smaller than plate reverbs and cost a lot less.
This is a spring reverb: springverb.mp3
The first reverb effects used a real physical space as a natural echo chamber. A loudspeaker would play the sound, and then a microphone would pick it up again, including the effects of reverb. Although this is still a common technique, it requires a dedicated soundproofed room, and varying the reverb time is difficult.
This is a chamber: Chamber.mp3
These three types of reverb are all available in digital form in addition to a few other styles simulating real spaces, and others not found in nature.
Natural Reverb Types
Room – A room is anything from a classroom to conference room. There is generally a short decay time of about 1 second: room.mp3
Hall – A hall is larger than a room, it could be from a small theatre with 1 second of decay up to a large concert hall with a decay time up to 2.5 seconds: hall.mp3
Church – The decay time of a church can vary between 1.5 seconds to 2.5 seconds: church.mp3
And Cathedral decay times can go above 3.5 seconds: cathedral.mp3
Remember, the sound of a room is not just the decay time. The materials it was built with make a huge impact on the character of the sound. Stone, wood, metal and tile all sound drastically different.
There’s also a few other types of reverb that are not natural - these are Non Linear, Gated and Reversed.
Non-Linear has a decay that doesn’t obey the laws of physics: non-lin.mp4
Gated was a popular effect in the 1980s, but it’s sounding pretty cheesy these days: gated.mp3
Reversed sounds like this: reverse.mp3
Reverb Parameters
Reverb Type – What kind of reverb emulation it is. There are Halls, Rooms, Chambers, Plates, etc…
Size – What the physical size of the space is. This can range from small through large.
Diffusion – How far apart the reflections are from each other.
Pre-Delay – Sets a time delay between the direct signal and the start of the reverb
Decay Time -Also known as RT60, which is how long it takes for the signal to reduce in amplitude 60 decibels.
Mix (Wet/Dry) – Sets the balance between the dry signal and the effect signal. When you have the reverb effect on an insert you need to adjust the wet and dry ratio, when you are sharing the reverb in a send and return configuration you want the mix to be 100 percent wet.
Early Reflection Level – Controls the level of the first reflection you hear. Early reflections help determine the dimensions of the room.
High Frequency Roll Off – Helps control the decay of high frequencies (as it is found in natural reverb).
Tips For Using Reverb
—Using pre delay can help keep your vocals up front, while still giving them space.
—Try to keep decay times short for faster tempo music.
—Filter out low frequencies before the reverb to keep it from sounding muddy
—Try de-essing the reverb to reduce harsh sibilance.
Jon Tidey is a Producer/Engineer who runs his own studio, EPIC Sounds, and enjoys writing about audio on his blog AudioGeekZine.com. To comment or ask questions about this article go here.
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