General Audio Processing EffectsA brief explanation of the most frequently used audio effects and processing methods.
Equalization is the process of boosting or cutting certain frequencies in a sound. This can be done with both hardware and software “Equalizers”, and typically involves either a parametric equalizer, graphics equalizer, or rolloff (high / low pass filters). Even if you aren’t an audio engineer, you’ve probably used some form of equalization. If you’ve ever turned up the bass or treble on a car stereo you have experienced sound EQ.
For more on Sound Equalization: What is a Sound Equalizer? (Sound EQ Guide)
Compression essentially destroys the dynamic range of an audio signal. As bad as that sounds, this is a very common and useful processing effect. An easy way of understanding compression is thinking of it as leveling out the loudest parts of a sound, or reducing the differences in volume throughout the sound. Too much compression can make audio sound “squished” or unnatural, but correct use of compression can make a sound’s perceived volume louder even at lower levels.
For more on Sound Compression: A Totally Different Way Of Understanding Compression
Limiting is like compression on steroids. Instead of simply reducing the volume of the peaks (or louder parts) in a sound, limiting forces anything over a certain threshold down to the same level. This involves setting a cut-off level that the sound cannot go over.
Expansion increases the dynamic range of a signal (Opposite of compression). Louder signals remain relatively close to the same levels, while lower level signals are reduced. This increases the range between quiet and loud sections of a sound.
Noise Gating is precisely the opposite of limiting. When a noise gate is applied, any sound below a certain level is removed, while all sound that is louder than the set level remains. Think about when a microphone is picking up “room noise”. A Noise gate can remove the subtle noise of a room and only allow the louder vocals or instrument sound to pass through (the gate…?). Unfortunately setting the threshold too high can create an unnatural sounding removal of sound that you did want to make it through.
Delay / Echo
Delay in it’s simplest form is an echo. Typically a delay effect allows you to set the time (distance between the original sound and the echo), the number of echoes, and several other parameters such as panning (left to right) or filters (high and low pass). Generally the echoes gradually reduce in volume, going from the original sound source’s volume to a barely audible signal. Most time based effects (reverb, chorus, phase, flange) are more complex forms of delay.
Sound reverberation is the emulation of the way a sound bounces around in a room or reflects off the surfaces of a room. Digitally generated sounds don’t actually exist inside a room until they leave your speakers so when you apply reverb you are pretty much creating a virtual room for your sound. Reverb also occurs naturally, for example when you yell in a large auditorium and hear the sound come back to you at different levels based upon the distance it has to travel before making it back to your ears along with the types of surfaces that it’s reflecting off of (certain surfaces are highly reflective while others absorb sound).
For more on Audio Reverberation: Bouncing Off The Walls – Sound Reverb Guide
Chorus effects create the illusion that one sound source is actually multiple sources. For instance, applying chorus to one vocal track could make it appear as though 5 people had been singing as opposed to the one person who really did. The way chorus achieves this illusion is by generating numerous delays to the sound, where each delay varies slightly in length and pitch.
Phasing & Flanging
Phasing is an effect that involves taking 2 versions of the same waveform and slightly offsetting them in time (or shifting them) so that the same peaks in the frequencies of the sounds occur in exactly the same way (since they’re the same sound) but at different times due to the offset or shifting. The interaction between the original sound and the phase shifted sound can create a “whooshing” effect as different parts of the frequency spectrum are amplified or reduced based on the time difference or degree of shifting that is occurring. At a specific point of shifting the two waves can actually cancel each other out (phase cancellation or antiphase) resulting in no sound at all as shown in the picture below.
Flanging is another form of phasing which uses notches that are spaced in a “harmonic” way relative to the way musical notes are spread across the range of frequencies.