13. Digital Signal Processing

Categories of DSP
DSP (Digital Signal Processing) is the technique of manipulating a sound and can be divided into 2 main categories depending upon the function.
1) Effects DSP: The purpose is to change the colour or timbre of a sound, e.g. Delay, Phaser, Distortion, Cut Off.  Effects DSP is covered in this chapter.

2) Mastering DSP: The purpose is to enhance the audible quality, frequency balance, clarity and loudness, e.g. Compressor, Limiter, Reverb and EQ.  Mastering is covered in Chapter 14

Most DSP effects can be used in both categories, e.g. an EQ can be used to ensure that the frequency range is balanced for mastering.  An EQ can be used to add a sweeping motion to a synth.




Effects and Mastering DSP

The following classification of effects can be applied to any sound source. 





Reduces the dynamic range or the quietest point to the loudest point


e.g. overdrive, distortion, but crusher etc

EQ band pass

Equalization filter that passes frequencies within a certain range and rejects all other.

EQ hi pass

Equalization filter that passes on frequencies above a certain range.

EQ low pass

Equalization filter that passes on frequencies only below a certain range.

Filter - Stereo Spread

a. Stereo Spread high frequencies - automation left to right
c. As above with auto filter resonance for added squelch

Fuzz Wah

Cut off and distortion, similar to a Wah Wah pedal.


Create the illusion of space by adding the ambience of different spaces, e.g. small room, hall, and cathedral.


Rhythmic amplitude modulation


e.g. Phase, Flanger, etc


Left and Right or spatial surround (if you have the technology)

Pitch Shifter

Pitch Shifter

Time Stretch

Tiny grains of a sound are looped to stretch the sound (old hardcore)


A vocal sound is processed though ring modulation.



Applying Filters to Instruments
Even the most simplistic sounds can be manipulated using filters to turn them into pro studio quality.  Once a few core techniques have been established, they can be used for Bass, Leads, Vocals and SFX.


Fig 1: A simple Bass sequence is programmed.  By itself, the Saw Wave timbre is very static and uninteresting.

Filters Bass 1 Raw.mp3



Fig 2: A Band Pass Cut Off filter is modulated using track automation.

Filters Bass 2 Modulation.mp3


Fig 3: A Stereo Delay filter is added.

Filters Bass 3 Stereo Delay.mp3