Modulation: CHORUS AND FLANGE

 Just as a chorus is a group of singers, the chorus effect can make a single instrument sound like there are actually several instruments being played.  It adds some thickness to the sound, and is often described as 'lush' or 'rich'.

 Two people playing an instrument together are almost never exactly the same  A chorus effect emulates this effect  It makes the sound of multiple musicians out of one

 There are two effects happening:  DELAY LINES and DETUNING  This creates what is called a VARIABLE LENGTH DELAY LINE  The 'variable length' part just means that the delay time changes over time

 On analog devices, changing the SPEED always changes the PITCH  A longer delay line will be LOWER in pitch  A shorter delay line will be HIGHER in pitch: The ‘munchkin’ effect  Think of copies of this tape being played simultaneously

 So now, by mixing this delayed and pitch modulated copy of the input together with the original, we have the chorus effect.

 A CHORUS is like a FLANGER (we’ll discuss this shortly)  A CHORUS has delay lines somewhere between 20 ms. and 30 ms.  This longer delay doesn't produce the characteristic sweeping sound of the flanger.

Chorus Parameters  The delay parameter simply controls the amount of delay used.  More specifically, it actually controls the minimum delay time that is used.  As the delay becomes very small, the chorus will act as a flanger.  Typical delay times range between 20 and 30 ms.

 Sweep Depth/Width (or RATE)  The sweep depth controls how much the total delay time changes over time.  It is usually expressed in milliseconds, and the sum of the sweep depth and delay parameters is the maximum delay used in processing the signal.

The delay used in the chorus is the sum of the delay and sweep depth parameters, where the latter changes over time.

 The sweep depth also increases the pitch modulation introduced by the time-varying delay line.  This happens because you have to read even faster and slower to cover the total change in time.  Large sweep depths will create a 'warble.‘

Types of Modulation Movement

 The sine is a very smooth function, and is always changing so the pitch is constantly changing as well.

 The triangle on the other hand only produces two pitches because the slope only takes on two different values, and the change between the pitches is sudden.

 The log waveform is smooth over it's cycle, but there is a jump at the end of each cycle.  Since the slope at the beginning and end of the waveform are different, there is an abrupt change in the pitch as well.  Advanced processors give these options

A sustained note processed with a chorus using three different LFO waveforms - a sinewave, triangle, and a logarithm curve.

 Typically a multi-voice chorus uses different Phases for each voice  This means that at any point in time, each voice is at a different point along the waveform, so they have different delay times.  If all the voices were in phase, it would have the same effect as a single voice chorus with an increased level.

 Flanging has a very characteristic sound that many people refer to as a "whooshing" sound, or a sound similar to the sound of a jet plane flying overhead.  Flanging is generally considered a particular type of phasing  As will be shown, flanging creates a set of equally spaced notches in the audio spectrum.

 Most modern day flangers let you shape the sound by allowing you to control how much of the delayed signal is added to the original, which is usually referred to as a 'depth' control (or 'mix')

 When we listen to a flanged signal, we don't hear an echo because the delay is so short  A flanger has a delay from 1-10 ms  This is SHORTER than a chorus  This frequency response is sometimes called a comb filter, as its notches resemble the teeth on a comb.

 Depth (Mix)  This is the depth parameter referred to above. The larger the depth, the more pronounced the notches in the flanger.  In multieffects units, the depth may only be controllable in the mixer section, and not available within the flanging processor. Some people use the term 'mix' interchangeably with 'depth'.

 Delay  The delay parameter specifies the minimum delay used on the copy of the input signal - as the delay changes, this will be the smallest delay.  In other cases, you may not be able to control delay parameter.

 Sweep Depth (Width):  The sweep depth determines how wide the sweep is in terms of delay time  This sweep depth is the maximum additional delay that is added to the signal in addition to the delay in the delay parameter. It determines how low the first notch in the frequency response will reach.

The relationship between the sweep depth and delay parameters.

 Feedback/Regeneration:  Some units will give you an option for taking a portion of the flanger's output and routing it to the input.  In some cases, you can also specify whether to add or subtract the feedback signal.  A large amount of feedback can create a very 'metallic' and 'intense' sound

 Speed/Rate:  How many times per second the notches sweep up and down.  The speed also affects the amount of pitch modulation.  By increasing the speed, the flanger will have to sweep through the depth in less time.