If you ever enjoyed the chiming sound of a twelve string guitar, or been impressed by the fullness of the sound created by two or more guitars playing together, then you already learned to value the effect chorus pedals create.
The chorus effect can make a single guitar sound like there are actually several instruments being played, adding thickness to the sound.
Let's analyze what happens when two people play instruments in unison. They will not play in precise synchronization and there will be some delay between the sounds they produce. The pitch of the two instruments will also deviate a little.
This effect can be easily implemented with a delay line controlled by a Low Frequency Oscillator (LFO). The delay is set to approximately 20 milliseconds and the LFO constantly varies this time with +/- 0-5ms.
The LFO waveform changes slowly (less then 3 Hz). The chorus sound can be controlled by changing this waveform's amplitude, frequency and shape.
The sine waveform produces a very smooth sound as the pitch is constantly changing.
The triangle LFO only produces two pitches and the change between the pitches is sudden.
The log wave is smoother, but there is a jump at the end of each cycle with an abrupt change in the pitch as well.
Example circuit: see the schematic diagram of the Boss CE-2 chorus pedal - a good quality analog chorus from the late 70s and early 80s, designed around the MN3007 (1024 stage BBD) and the MN3101 (clock driver IC).
Common knobs in chorus pedals:
The delay knob controls the minimum delay time that is used. If you set the delay to a very small value, the chorus will act as a flanger. Optimal delay times range between 20 and 30 ms.
The sweep/depth control sets how much the total delay time changes over time (the amplitude of the LFO). The sum of the sweep depth and delay parameters is the maximum delay used in processing the signal. The sweep depth also increases the pitch modulation introduced by the delay line and large sweep depths will create a "warble."
The speed/rate control sets the LFO frequency. It adjusts the rate at which the LFO waveform repeats itself, affecting the pitch modulation too. Increasing the speed rate is equivalent to compressing the LFO waveform in time, which makes it steeper, giving more pitch modulation.
The Arion SCH-Z is a pretty good sounding chorus pedal using BBD technology, a close relative of the legendary SCH-1.
Even though it does not sound exactly like the SCH-1, the SCH-Z is still a very good chorus pedal, and it has its strengths in some areas. The chorus is extremely warm and you can also produce a great Leslie sound with it.
With the DigiTech XMC Multi Voice Chorus Pedal you can morph through a whole range of voices for an almost unlimited supply of lush multi-voice sounds.
The Multi-Chorus features Level, Speed, Depth, and Voice controls and the outputs include Left/Mono and Right.
The CE-5 Chorus Ensemble is a high quality chorus effect covering a wide frequency range and featuring low- and high-cut filters. This lets you create any kind of chorus effect from a mild, natural chorus to the clear and penetrating stereo chorus effect popular in contemporary music.