At the heart of what we call "effects" in professional audio is the delaying of sound.
Virtually any audio effect - reverb, flanging, chorusing, phaser, echoing, looping, etc. - uses (and manipulates) delay in one form or another.
You've probably heard the repetition of a person's words in a large canyon.
The first sound is the voice arriving directly to our ears, and then moments later, the voice repeats after the sound wave has traveled across the canyon and back to our ears. There is a delay to that sound caused by the time it takes to travel (at roughly 1,130 feet per second) out to the canyon wall and back.
This same type of delayed echo of a sound occurs in a room as well, and is caused by the sound reflecting off of surfaces in the room and finding its way back to our ears.
We will hear the original sound as a reference, and this is quickly followed by the early reflections (or echoes).
The apparent nature of these echoes is relative to how loud they are, as well as their arrival time. The loudness is a function of the material reflecting the sound, and this can also alter the frequency content because material may reflect certain frequencies quite well and yet absorb others.
The arrival time back at the listener's ears is a function of how far the sound had to travel through its reflected path to arrive at our ears, and is of course relative to the arrival of the direct sound.
Some reflections may not even be able to be heard, even though they can be measured and proven to be quite loud by comparison.
If the sound is delayed in time less than about 30 milliseconds, our brain will not perceive it as a discreet echo.
So, reflections arriving less than 30 milliseconds after the direct sound arrives might be considered early reflections. Reflections that arrive later will generally be heard as discreet echoes. This effect is typically more noticeable with sounds that have a percussive attack.
When you clap your hands in a large auditorium, you may notice a smoothly decaying sound that lingers for a moment.
This is know as reverberation, and is made up of many hundreds of reflections arriving at the listener's ears, so closely spaced in time that he cannot perceive them as separate echoes, but rather as a homogeneous mixture of all of them.
Each room has it's own reverberation "sound," determined by the acoustics of the room.
That is to say, the manner in which the room is constructed, how large it is, if the surfaces are hard or soft, reflective or absorbent, and even whether it's painted or not, and so forth, give the room its character.
"Proper" design usually presents a reverberant field that is quite diffuse, with all frequencies decaying smoothly together, with no one frequency louder than another.
With a sound reinforcement system, any of these acoustic properties can be presented at the touch of a button on a digital effects processor.
They offer any of the effects described above, along with a long list of other, more imaginative or not-exactly-natural-on-the-planet-I-know-and-love effects.
Room Simulation
Rather inventive techniques to simulate acoustic environments have been available for years.
It's not my intent to go into the history of these devices, but we should look at some prominent devices and concepts from the past.
Properly built, one of the best room simulators is an echo chamber. And that's exactly what it is - a room simulator.
Common in recording, it's a highly reflective or "live" sounding room constructed to provide controlled reverb on demand. This echo chamber room will have one or two loudspeakers placed inside it, and one or two microphones as well.
Simply, the audio signal is fed to the loudspeakers, the sound then washes around the room, reflecting off the many surfaces, and is picked up by the mics. The signal from the mics is then brought back into the recording console.
The loudspeakers and/or mics can be repositioned to "shape" the desired reverb sound. (Notice that the effect obtained is termed "reverb" - not "echo" which is just an audio terminology quirk.)
Another device popular in the past is the reverb plate. Ones of better quality sound so good that they're still in use today alongside the more flexible digital effects processors.
The theory is similar to the echo chamber - one or two mics (pickups) capture sound from a loudspeaker driver, although this time they're mounted to a large steel plate. (For more details about plate reverb design, see Bob Buontempo's fine article here.)
However, with the reverb plate, the "room" is a sheet of metal. The loudspeaker is actually a specially designed transducer virtually attached to the plate near its center.
When an audio signal is fed via an amplifier to this transducer, it causes the plate to vibrate, and two contact microphones attached to the plate in optimum locations pick up these vibrations. The signal from those mics is also carried back to the recording console and inserted into the mix.
Over the years, many different methods have been tried to delay an audio signal for a moment before it is "allowed" it to be heard.
One brute force method was simply attaching a mid-range driver at one end of a long tube (so long it had to be coiled in order to be practical), with a mic placed at the other end to pick up the sound.
Hardly considered flexible, this device found its best use as a signal delay for underbalcony systems, improving intelligibility for those farther away from the output of the main loudspeakers.
Another delay device was the early Echoplex, which simply used a small audio tape recorder and a moveable playback head to alter the length of time before the "delayed" signal was heard.
Analog delay devices also gained popularity by eliminating the tape. These devices use a simple "bucket brigade" technique - the signal is stored very briefly in an analog "memory" and then released.
By chaining several of these memories together, the signal can be held for quite a while.
And by providing different points at which to "tap" the chain, a more complex output signal can be achieved. Many of these devices sound quite good and can still be found in use today. The major drawbacks are increased noise and limited bandwidth.
Marching Onward
Believe it or not, but digital effects processors were introduced way back in the mid 1970s, and although these offered simple operation and a unique sound, they were still priced high at $7,000 to $12,000.
As computer technology has marched onward, excellent quality devices that rival and supersede those early ones can be had for a fraction of the price.
The limiting factor on many of the early digital units was bandwidth, going only go as high as 10kHz to 12kHz.
Of course, the argument is that natural reverb rarely contains frequencies above those limits due to the natural friction of air, which dissipates the higher frequencies.
Still, the desire lurks inside of every engineer to create some rather extraterrestrial effect, and advances have been made to increase that bandwidth.
Another limiting factor was that sound was often "grainy" - one could easily hear the "stepped" sound of the digital conversion. Again, advancements have been made in sampling rate and smoothing techniques.
Shape & Define
Quite literally, when mixing an album I imagine a place where this performance is taking place, and then use the effects processors to help shape or define that place.
Similarly, doing a sound reinforcement mix (to me, at least) is really just mixing the album in front of an audience instead of in a small control room.
As long as the room is large enough and relatively well behaved acoustically, I approach the use of digital effects processors in exactly the same way as during a mix-down session.
The secret to tasteful use of effects is to listen very closely to your favorite recordings.
Carefully analyze what you hear, and then try to emulate it.
And remember - a little bit of effects can go a long way. Don't overdo it!
Curt Taipale of Taipale Media Systems heads up Church Soundcheck.com, a thriving community dedicated to helping technical worship personnel, as well as theChurch Sound Boot Camp series of educational classes held regularly throughout the U.S.