Flanger/Chorus
Simply put, the flanging effect is created by using duplicating a dry signal, passing one through a constantly changing delay and feeding it back with the other signal. This time delay is usually less than 20ms so is would not come across as a typical delay. This delay has a filtering effect on the signal and this creates a series of notches called a comb filter. This is very similar to other filters except this is continually moving to give a very fluid motion. The only difference between a flanger and a chorus is that the flangers use less delay and have a feedback parameter.
Common Parameters
Depth - Adjusts the intensity of the flange effect. High settings of depth combined with high settings of feedback usually produce dramatic, synth-like results. Varies from 0 to 30ms. This is sometimes referred to as mix.
Delay - This specified the minimum amount of delay on the the copy of the original signal.
Sweep Depth - The sweep depth determines how wide the sweep is in terms of delay time. This essentially controls how big the sweep's comb filter will be.
LFO Waveform - In some cases, LFO waveforms can be chosen (sine, square etc) as they are used in the sound synthesis.
Feedback - This controls how much of the flanged signal is fed back to the input of the unit. The feedback parameter is what gives flangers their distinctive voice. Flangers are capable of both negative and positive feedback loops.
Speed/Rate - This controls the speed of the LFO. This also controls the amount of pitch modulation. Increasing the speed means that the flanger will sweep through the depth in less time.