Chorus
Description
The chorus effect combines
the input signal with one or more frequency-modulated delayed copies of itself.
The delay times are varied using a low-frequency oscillator. The typical delay
range for chorus is between 20ms and 30 ms. Parameters controlled by the user
are delay time, delay depth, wet signal gain, type of low-frequency oscillator
waveform, and oscillator frequency. Chorus can make a sound richer by adding
depth. Several slight variations of the original input signal played together
sound like multiple instruments playing the same part.
Graphical Depiction
This graphic depicts a
two-voice chorus. The original signal is combined with a modified copy of
itself. The modifications are based on parameters selected by the user – the
range of delay time, oscillator type, and oscillator frequency. Additional
voices can be added each with their own parameters.
Effect Formula
|
y[n] = x[n] +
x[n-m] |
|
m = delay time in
samples |
|
m = sr *
([maxDelay - minDelay] * [1/2 sin(ft)+1/2] + minDelay) |
|
sr = sampling rate
(Hz) |
|
maxDelay = maximum
delay time (sec) |
|
minDelay = minimum
delay time (sec) |
|
f = oscillator
frequency (Hz) |
|
t = time (sec) |
Source Code
(.csd files can be viewed with Notepad or any text
editor)
Example Audio Clips
|
Original Unprocessed
Signal |
|
|
Oscillator = sine Oscillator Freq = 0.5 Hz Delay time = 30 ms Depth = 1 ms Wet Gain = 1 |
|
|
Oscillator = sine Oscillator Freq = 3 Hz Delay time = 20 ms Depth = 3 ms Wet Gain = 1 |
|
|
Oscillator = sine Oscillator Freq = linearly
increasing Delay time = 20 ms Depth = 30 ms Wet Gain = 1 |
References
Lehman, Scott
(1996). Effects Explained. Harmony Central. Retrieved 6/04 from
http://www.harmony-central.com/Effects/effects-explained.html
Mikelson, Hans
(2000). Modeling a multieffects processor in Csound. In Boulanger,
Richard (2000), The Csound book (pp 575-594). Cambridge, MA: MIT Press.
Schindler,
Allan. (1998). Eastman Csound tutorial.
Eastman School of Music. Retrieved 6/04 from
http://www.esm.rochester.edu/onlinedocs/allan.cs/
Vercoe, Barry.
(1992). The public Csound reference manual, version 4.16. MIT Press. Retrieved 6/04 from http://www.lakewoodsound.com/csound/hypertext/manual.htm
Zolzer, Udo.
(2002). Digital audio effects. West Sussex, England: Baffins Lane.