FX Processing

Question 1

Explain Chorus.

Answer 1

◦ When signal enters a chorus plug-in, a copy (or several copies) of the signal will be made. This signal is exactly the same as the original
signal in amplitude, frequency, and phase position.
◦ The copied signal is then slightly delayed. This creates a difference in the phase of the two signals, the original and the copy.
◦ Next, the amount of delay time is modulated with an LFO. This causes gradual changes in the frequency (wavelength) of the
resulting signal. Like the “Doppler Effect,” this will have the effect of varying the copy’s pitch. This delayed, modulated copy is then
mixed with the original signal.
◦ The result is that the copy (or copies, depending on the chorus unit) slightly varies from the original in pitch and time. This is used to imitate the effect of multiple instruments or singers, who would never
be perfectly aligned with each other in the real world.

Question 2

What is chorus used for?

Answer 2

Chorus is best used to wash a sound out and make it more ambient.

Question 3

Explain what a flanger is.

Answer 3

Like in chorus, flangers create a copy of the original signal and delay it. Flangers require much shorter delay times.
◦ An LFO is then applied to modulate the delay time. Like chorus, we now have a copy of the original signal with a modulated delay time. This copy is then mixed with the original signal.
◦ Because the copies of audio are identical, interference will begin to occur. Resonances will be created at some frequencies, but more noticeably, a series of notches (notch filters) will also be created across the frequency spectrum. Due to its shape, this is called a comb filter

Question 4

What is a comb filter?

Answer 4

The type of filter that occurs in flangers and chorus. A series of notch filters.

Question 5

Where are the notches created in flangers and chorus’ respectively.

Answer 5

Flangers = high end. (fast delay time)
Chorus = low end (longer delay times)

Question 6

What is a flanger commonly used on?

Answer 6

• Hi Hats.
• Pads
• Guitars.

Question 7

Explain what a phaser is.

Answer 7

A copy of the original signal is made. Instead of delaying the signal, however, it is passed through a circuit called an “all-pass filter.” This type of filter does not affect the level of
frequency content in the signal but does introduce a phase shift around a set frequency.
◦ Connecting another all-pass filter afterwards would create a single notch (one tooth of a comb filter). Phasers work by stringing
several all-pass filters together in series to create a series of nonharmonically related notch filters.
◦ An LFO can then be used to modulate these notch filters, similar to the motion in a flanger. Due to the inharmonic relationship between the phaser’s notch filters, the effect sounds more gentle—between that of the chorus and flanger.

Question 8

Name two types of delay.

Answer 8

Timed delay and slap delay

Question 9

What is timed delay?

Answer 9

• Long delay, that stays in time with the
  music.
• BPM synced
• Mainly vocal and guitar use.
• Often employs many repeats (hi
  feedback)

Question 10

What is slap delay

Answer 10

• Short
• Un-timed delay.
• Short single repeat delay 35 – 500ms.
• Can provide a huge range of effects
• Become popular in the 1950’s (Elvis slap
  echo)
• And is still used today extensively to
  provide depth and size.

Question 11

What does amp modelling allow you to do?

Answer 11

Allow for DI guitar recordings
to sound like they are being recorded
through a real amp.

Question 12

How do amp modellers achieve their realistic sound?

Answer 12

By using impulse response recordings of real amp cabinets.