Introduction
There are two main types of sound effect generators: Hardware signal processors and plugins, software based effect generator which integrated into an audio sequencer and can be run in real-time on a computer. As the power of modern CPUs and sound cards have been growing recently at an exponential rate, plugins have been overtaking the market for the past few years. Plugins are also included in most audio sequencers and there are a large number of freeware plugins available on the internet.
How do audio effects work?
Modern effect generators use algorithms to process audio signals. An algorithm is a mathematical routine, which describes how a signal is to be manipulated. This routine is applied to an input signal and results in an altered output signal.
Types of effects
Most audio effect can be placed into one of the following categories:
1. Delay effects
2. Reverb effects
3. Distortion effects
On the following pages we will take a closer look at these four categories and examine typical effects and how to use them.
Delay
What does delay do?
Delay is a discrete repetition of a sound. A “real world” example of this is when you stand at some distance from a wall and clap your hands. Depending on how far away you are from the wall, after a small time interval, the sound echoes back. The delay time is determined by the time it takes the sound to reach the wall and return.
Digital delays save the original signal, and after a specified time begin playback of the saved signal. The maximum delay time is determined my the amount of memory the device has. Repeated delays are achieved by routing the delayed output signal back to the input.
Typical parameters:
I. Feedback
This parameter specifies (usually in %), the amount of the delayed output signal is to be routed back to the input. This is used to create multiple echoes.
II. Delay time
Specifies the amount of time between the input signal and playback of the delayed output signal.
III. Mix
Specifies the ratio between input signal and effect signal.
Delay techniques
I. Slapback Delay
A slapback delay refers to a single repetition of the signal (no feedback) with a small delay time of between about 35ms and 100ms. Delay times larger than this are usually referred to as an echo.
II. Multi-Tap Delay
A multi-tap delay is a bit more versatile than a simple delay. Multi-tap delays allow the user to create rhythmic patterns in the delay as opposed to having a fixed time for every recurring delay. These can add a rhythmic element to a song, similar to other rhythmic instruments.
III. Ping-Pong Delay
A ping-pong delay is a form of multi-tap delay in which a signal bounces back and forth between the left and the right channel. As opposed to other delay effects this method requires a stereo output with two delay lines. Each channel then has a different delay time letting the delayed signal alter from the left side to the right.
Reverberation (Reverb)
Reverberation or reverb is probably one of the most often used audio effects.
What is reverberation?
Reverberation is basically the same as a delay, the difference being that it does not come from one single source but from multiple ones ( for example the walls of a room). Each delay time depends on the times it takes for each reflection to return to the listener. these multiple reflections build up and blend together creating reverberation or reverb. A good place to experience reverberation is in large rooms, for example in a church. A listener can hear the remainder of the sound as reverberation for some time after the sound itself has ceased. The characteristics of the reverberation give the listener an idea of the room in which the reverberation is created, including the size of the room and the distance between the listener and the sound source.
Why use reverberation
Reverberation is all around us even if we don’t notice it. Whenever we speak in a room or visit a classical orchestra, the rooms we are in produce reverberation. A recording therefore, which has no reverberation can sound very unnatural and “dry”. Using reverb on instruments or vocal recordings can also add an “atmosphere” to the recording, giving the listener an impression of the surroundings of the artist.
Typical parameters:
I. Predelay
Predelay is the amount of time (in ms) it takes before the first reflections of a signal are heard. This parameter can be used to place a sound either closer or farther away from the listener. Sounds that have a short predelay give the impression to be closer to the listener than sounds with a longer predelay. One could give a singer a short predelay and the drum set a long one, giving the impression that the drum set is behind the singer.
II. Reverb time
This parameter sets the time in which the reverberation of a signal can be heard.
Distortion
Distortion is a very common effect, its most well known use being on electric guitars.
What does distortion do?
Simply put a distortion effect takes a “clean” input signal and returns a distorted output signal. There are several methods in which this is accomplished. The simplest way is by simply cutting of the high amplitudes of a signal.
Clean input signal
Distorted output signal
Another method of distortion is tube distortion. Tube distortion is the distortion caused by vacuum tubes. Instead of chopping off the high amplitude parts of a signal, they are compressed taking some of the dynamics out of the top of the signal resulting in a form of distortion generally considered to be more pleasing to the ear.
Typical parameters
I. Drive
This parameter determines how much distortion the output signal should have.
II. Output
The volume of the output signal.