The Delay Spectrum

For this week's assignment in the Introduction to Music Production class on Coursera, I'm going to demonstrate the effect of short delays on the frequency spectrum of a sound.  I will also demonstrate how to effectively use medium and long delays to enhance a piece of music.

When a sound is combined with a slightly delayed copy of itself, the interaction between the waveforms creates an interference pattern that results in notches in the output signal.  This effect is known as comb filtering.  In the following video, I start by playing an unprocessed white noise signal.  Then, I turn on a delay set to one millisecond with a dry/wet mix of 50%.  The result is a series of notches in the output.  Finally, I slowly increase the delay time to two, three, four, and five milliseconds.  With each increase in delay time, more notches appear, and the notches are closer together:

The feedback parameter in a delay effect is used to send the output of the delay back into the effect, causing the sound to repeat.  When this is done in a short delay effect, the relatively high frequency of the repeated sound is perceived as a pitch.  In the following video, I start by playing an unprocessed drum sound.  Then, I apply a one millisecond delay and progressively increase the delay time by one millisecond at a time.  Each increase in delay time causes more overtones to appear, and the perceived pitch drops:

A medium-length delay can be used to achieve a slapback effect, which simulates what happens when a sound bounces off of a hard surface.  In the next video, I start with an unprocessed drum track, and I apply an 80 millisecond delay.  Initially, the dry/wet mix is set to zero, so I increase the amount of wet signal until the effect adds a sense of space to the drum kit.  Then, I slightly increase the delay time in the right channel in order to emulate being a different distance from two walls in the space:

A long delay can be used to add rhythmic interest to a melodic line.  In the final demonstration, I play the opening guitar part from The Electric Co. by U2 (I apologize for the lame guitar patch - I didn't have time to set up my real guitar).  Without the delay, it sounds dry and uninteresting.  I then turn on a 3/16-note delay that is synchronized to the tempo of the song.  Feedback is set to 50%, and a filter is applied to roll off the low end of the wet signal, differentiating the echoes from the original notes:

Thanks for watching!