Digital Audio effects

Digital waveforms can be altered in multiple ways to create innovative effects. Audio effects are based on few fundamental principles

• Amplitude Modulation
• Time Delay
• Waveform Shaping
• Frequencey modulation

Amplitude Modulation effects

Volume Control - The effect produced by varying the amplitude of the signal. The amplitude can
be cut down by attenuating the input signal and can be increased by using amplifiers.

Volume controls are useful for placing between effects, so that the relative volumes of the different effects can be kept at a constant level. However, most, if not all effects have volume controls built-in, allowing the user to adjust the volume of the output with the effect on relative to the volume of the unaffected signal (when the effect is off).

Compression
The compression effect amplifies the input signal in such a way that louder signals are amplified less, and softer signals are amplified more. It is essentially a variable gain amplifier, whose gain is inversely dependant on the volume of the input signal.
It is mostly used in studio recordings, to give the recording a constant volume, especially to vocals. Compression tends to increase background noise, especially during periods of silence. Thus, a noise gate is usually used in conjunction with the compressor.

Expansion
An expander performs the opposite effect of the compressor. This effect is used to increase the dynamic range of a signal.

Panning
Stereo recordings have two channels: left and right. The volume of each channel can be adjusted - this adjustment effectively adjusts the position of the perceived sound within the stereo field. The two extremes being: all sound completely on the left, or all sound completely on the right.
Usually the 'balance' knob on a music system does this.

Noice Gating
A noise gate, blocks input signals whose amplitude lies below a certain threshold, and lets other signals through. This is useful for eliminating background noises, such as hiss or hum, during periods of silence in a recording or performance.

Time Delay effects

Echo

Echo is produced by adding a time-delayed signal to the output. This produces a single echo. Multiple echoes are achieved by feeding the output of the echo unit back into it's input through and attenuator. The attenuator determines the decay of the echoes, which is how quickly each echo dies out.

Chorus

The chorus effect is so named because it makes the recording of a vocal track sound like it was sung by two or more people singing in chorus. This is achieved by adding a single delayed signal (echo) to the original input. However, the delay of this echo is varied continously between a minimum delay and maximum delay at a certain rate.

Reverb

Reverb effect is used to simulate the acoustical effect of rooms and enclosed buildings. In a room, for instance, sound is reflected off the walls, the ceiling and the floor. The sound heard at any given time is the sum of the sound from the source, as well as the reflected sound.

Flanging

Flanging is similar to chorus effect where delay of the echo is varied continuously, kind of extreme of chorus.

Phasing

When two signals that are identical, but out of phase, are added together, then the result is that they will cancel each other out. If, however, they are partially out of phase, then partial cancellations, and partial enhancements occur. This leads to the phasing effect.