Delay Basics

This page explains how to use Nyquist to add a feedback delay effect in Audacity.

Note: All [comments] and [explanations] are written in square brackets, so they cannot be confused with (Lisp code).

To add a feedback delay effect to an Audacity track with Nyquist, the easiest way is to use the Nyquist "feedback-delay" function:

(feedback-delay sound delay feedback)

The "feedback-delay" function applies feedback delay to sound. The delay must be a number (in seconds). The sample rate is the maximum from sound and feedback (if feedback is also a sound). The amount of feedback should be less than 1 to avoid an exponential increase in amplitude. Also since output is truncated at the stop time of sound, you may want to append some silence to sound to give the filter time to decay.

Example:

1. First either load a sound file into Audacity or record some.

2. Now click Tools -> Nyquist Prompt. A window with a text field will appear where you can type in:

;;"(sine 440)" generates a sinusoidal sound wave at 440Hz to be used as the feedback 
(feedback-delay *track* 0.7 (sine 440)) 

Do not forget to type the parens. The parens are part of the Lisp language Nyquist is based on. Without the parens the Nyquist Lisp interpreter will not be able to understand your code

See Prompt Basics for more info about the prompt.

After clicking "OK" in the "Nyquist Prompt" window the "feedback-delay" function will take the Audacity sound and return a output sound with a feedback delay of 0.7s throughout the sound. The result of the last computation of the Nyquist code always gets automatically returned to Audacity.

The ''*TRACK*''' variable is the Audacity "sound" [the selected part of the Audacity track]. Nyquist in Audacity always understands ''*TRACK*'' as the Audacity sound variable.

Try "feedback-delay" with longer or shorter delay times as well as different sounds for feedback. Nyquist provides many more functions to generate sounds besides the simple "sine" function. Look at Functions: Sound Synthesis for the complete list of these functions.