Delays, Combs and Pitch

Introduction

Today I am going to talk a about the delay spectrum, showing examples of comb filtering, creating pitches with delays, slapback delays and synchronized long delays.

The Delay Spectrum

Terms used in delay effects

The delay time is how long the signal is delayed before being mixed in with the original signal.

We have dry and wet signals in filtering. A wet signal is the delayed signal. The dry signal is the undelayed signal.

Feedback is how much of the wet signal is returned back to itself. This is a gain stage and increases the amount of feedback that can be heard, and the time that the signal will continue to be heard.

Comb Filtering

Comb Filter Frequency Response Diagram

A comb filter adds a delayed version of a signal to itself, causing constructive and destructive interference. The frequency response of a comb filter has a series of evenly spaced spikes, making it look similar to a comb.

In this diagram, you can see the comb like signal. There is a 1mS delay between the original signal and both wet and dry signals are at 0dB. Where the two signals peak together, you can see that signal have been increased by 6dB. Where the signals are opposite there is around a 100dB notch.

Creating Pitches with Delays

With feedback applied and a 1mS delay, a clicking signal will appear to have a pitch caused by the addition of the dry signal with the fed back wet signal. If the delay is slowly increased, the pitch will appear to have a lower frequency. This relationship between the delay and the percieved pitch is a core part of generating electronic music.

Slapback Delay

A slapback delay has a medium delay time, typically between 75 and 250mS with very little or no feedback. This gives the effect of having sound reflecting from a wall with no additional echo's, or in other words making a similar sound to a room.

Synchronised Long Delays

A long delay gives a distinct echo to the sound, that matches what we would find in nature. It is important to synchronise the delay to the underlying musical content, in time with the quater notes for example.

To aid the listener, the wet signal needs to sound distinct to the dry original signal. A long delay can clash with harmonies and complex rhythms, so long delays need to be applied carefully and only after ensuring that the delay enhances the musical experience.

Reflection

Although a delay is a very simple concept, in actuality they are very complex effects to set up and make a usable and beneficial improvement to a song.

I would like to thank those of you that have read through and commented on my work, and wish you well with your coursework. I am finding it hard to believe that we're rapidly approaching the end of this course!