Chorus Pedal User’s Guide
The last of the delay-based modulation effects we will discussing is the chorus unit. When two acoustic instruments play the same notes in unison there are fractional differences in each of their pitches and timing. These tiny discrepancies produce an effect called beating, an oscillation in volume equal to the difference in frequency between the two waves caused by alternating constructive and destructive interference. This is perceived as a “shimmering” quality. Guitarists take advantage of the beating effect when using harmonics to tune. As the tuning harmonics become more proximal, the beating effect slows until it is imperceptible.
Chorus effect pedals split a guitar’s signal then use an LFO to manipulate the amount of delay applied to the wet signal. Since the delay time is consistently shifting, it produces a Doppler effect, stretching the wavelength of the wet signal and dropping the pitch relative to the increase in delay time. Thus the frequency of the beating increases and decreases as the LFO moves through its range. This is similar to the process used in flanging with the principal differences being that chorus uses longer delay times and does not feed the wet signal back through processing.
While chorus was used as an electronic effect on Hammond organs as early as the 1940s, stage use of the chorus effect on electric guitars took off in the 1970s with release of the Roland Jazz Chorus amplifier. In 1976, Roland released the first chorus effects pedal with the Boss CE-1. In the subsequent decade usage of chorus would become so ubiquitous as to border on cliche.
Common Chorus Pedal Controls
Rate- Just like on a phaser or flanger, the rate knob controls the speed at which the LFO sweeps through its range.
Depth- Sets the maximum amount of delay applied to the wet signal and therefore the range of beating.
Level/Mix- Controls the ratio of wet signal re-combined with the dry signal and by proxy the intensity of the chorus effect.
EQ- Less commonly included than the previous three, EQ controls the frequency of the chorus effect.
Common Chorus Pedals
Boss CH-1- A pedalboard stalwart, this four control pedal from the inventors of the original Roland Jazz Chorus has survived generations of competitors. Its construction and utility is simple and straight-forward with the addition of a second output jack for splitting the signal between two amplifiers.
Electro-Harmonix Small Clone- This analog pedal is as fool-proof as many of its EHX siblings, with only one knob and one switch. The “RATE” knob controls the speed of modulation while a two-setting “DEPTH” switch allows the players to choose between a shallow and deep modulation. Despite its simplicity, this pedal can provide a wide palate and was a favorite of Kurt Cobain.
MXR Stereo Chorus- With five control knobs, dual outputs and a bass filter, this analog pedal provides an incredible amount of versatility. The EQ function is split into bass and treble potentiometers for more precise tone shaping. The addition of a bass filter allows the restriction of the chorus effect to higher end frequencies for the retention of low-end tone.
Common Chorus Settings
I’ll be taking these settings from the MXR Stereo Chorus manual since there is digital version in Amplitube 4 that allows me to demonstrate them to my students.
Thick Analog Chorus- This is the quintessential chorus sound, useful in a broad array of applications. There is just enough effect here to color the sound without being overwhelming. It is particularly great for adding texture to your rhythm parts.
Rush Distorted Chorus- By setting your chorus pedal to affect the higher frequencies and pairing it with a distortion pedal, you can make your dirtier guitar parts sound more dramatic.
Police Clean- No group better exemplifies tasteful use of chorus than The Police. This setting will really add bite to your lead and rhythm parts.
Signal Chain Placement
As a modulation effect, chorus is best placed after gain and filter effects, but before ambient effects. When using amplifier gain, it can be run out of the effects loop.