Time-Based Effects

Time in Audio

These effects take audio and move it around, often copying it onto other parts of the timeline. They can add depth to the sound, as if a performance was larger than life, or recorded in a different location. Sometimes it’s just to add some extra movement to keep things interesting. Some types of pitch shifter are also time-based. Common effects are delay/echo, chorus, flanger, phaser, pitch shifters/harmonizers, and the ever-present reverb.

 

Delay and Echo

This effect simply delays the sound by a period of time; though, admittedly, it’s far from simple. Delays can usually delay by a set amount of time or be in sync with the tempo of the song (quarter note, half note, etc . . .). You can have multiple delays that decay more with each one, and choose how much of the original and altered signals are mixed together. Once a delay overcomes the HAAS effect (at about 40 ms), it becomes an audible echo. This is usually accomplished via a delay plugin. Delays/echoes are regularly used on vocals, guitars, and other instruments to add interest or depth. Check out the audio demos in the resources area for each effect on this page.

One classic use for delay is to make sure all the speakers in a live PA system arrive at the audience at basically the same time. If a seat is 80 ft. from the main speakers, the little delay speakers nearest that seat must be delayed by about 71 ms. (sound travels at about 1130 fps.).

The delay plug-in used in the example in the resources area

Chorus

When multiple, similar sounds are perceived as one (without echoes), it’s a chorus. This happens naturally when 100 people sing together, and the chorus plug-in tries to emulate the same thing. It’s a common way to try to fatten up a source or add stereo imaging, though the copy/pitch shift/delay that a computer does isn’t nearly the same thing as having more performers. Chorus delay times are usually around 5-25ms. Chorusing, flanging, and phasing all create frequency notches in the signal (comb filtering), with phasers being the most discreet.

The chorus plug-in used in our example in the resources area

Flanger

Flanging is when a signal is doubled with a dynamically delayed copy of itself; the delay is usually 0.1-5ms. The resulting comb filtering changes with the speed of the flanger. It came about after John Lennon had his chief technician (Ken Townsend) come up with a way to double Lennon’s voice without recording it twice; they set up two tape recorders, then discovered a new effect when you press down on the flange of one of the recorders (slowing it down slightly).

The flanger plug-in used in our example in the resources area

Phaser

A phaser is much like a flanger in that it creates a comb filter effect. It does this by copying the signal, then altering the phase of one of the signals. The phase alteration is often triggered by a sine wave LFO.

The phaser plug-in used in our example in the resources area

Pitch Shifter

This effect has a few implementations. The simplest is playing audio back at a different speed than what it was recorded. This causes the pitch to rise when sped up and lower when slowed down. Modern pitch shifters can alter pitch without altering playback speed. A harmonizer is a pitch shifter that creates multiple pitches and combines them into polyphony/harmony (at least one new pitch mixed with the original).

The harmonizer plug-in used in our example in the resources area

A digital emulation of the Eventide H910 Harmonizer.

Reverberation

This is probably the most lauded effect in pro audio. Reverberation consists of the reflections and decays of sound in a space. As a plug-in, reverb is essentially a multi delay. It either creates some cool effects or attempts to place the sound in a space other than where it was recorded. For example, many of the more expensive virtual instruments will include presets for Air Lyndhurst or Abbey Road Studios, even though the sounds weren’t recorded in those locations.

Plate Reverbs: These were physical metal plates that vibrated in tandem with music via an electromechanical transducer. The vibrations were picked up, then added to the original, dry signal. Naturally, that’s the sound that a digital plate reverbs attempts to emulate.

Spring Reverbs: These were enclosed springs that received an input signal on one end that was picked up on the other end. The vibration of the spring caused the reverberant effect. Sometimes it was shaken during playback, creating a thundering effect.

Common Digital Reverbs: These use various algorithms to emulate plates, springs, and rooms. A reverbs pre-delay is the difference between the arrival of direct audio and the first reflections to the listener.

Convolution Reverb: This resource-heavy process applies a sampled space to every sample of an audio file. Spaces are sampled with a gunshot, wood slap, or tone generators, then the originally signal is canceled out with a phase-inverted version of itself. This leaves just the reverberation in the form of an audio file, known as an impulse response. Convolution reverbs generally get the most accurate representation of a space and a large host of impulse response waves are freely available online.

An impulse response from a performance hall.

An impulse response from a performance hall. Note that high frequencies decay quicker than low frequencies.