Modulation Based Effects

Question 1

What are the five types of modulation based effects processors?

Answer 1

• flanging
• phase shifting
• auto-pan
• tremolo
• vibrato

Question 2

What is phase shifting and how does it work (3 steps)?

Answer 2

sweeping notch filter effect

• low frequency oscillator modulates a variable all-pass filter phase-shift network
• shifted signal is combined with the dry signal
• changing phase relationships between two signals create sweeping notch producing phase cancellations

Question 3

What is the equation for notches in a phase shifter?

Answer 3

notches=stages/2

Question 4

How many notches does a 4-phase phase shifter yield?

Answer 4

4 stages yields 2 notches

Question 5

What is flanging and how does it work?

Answer 5

sweeping comb filter effect

• low-frequency oscillator modulates a very short time delay
• delayed signal is combined with the dry signal
• time relationships between two signals creates multiple phase cancellations (moving comb filter)

Question 6

How does one create a flanging effect?

Answer 6

• set delay time between .5 and 10 ms
• set depth to max
• set feedback to 30-65%

Question 7

How does auto pan work?

Answer 7

• inverse amplitude modulation across two channels
• pan law is in effect

Question 8

What is the difference between tremolo and vibrato?

Answer 8

• tremolo is amplitude modulation
• vibrato is frequency modulation

Question 9

What are the four types of pitch-based processors?

Answer 9

• chorusing
• pitch correction
• pitch-shifting
• harmonizing

Question 10

What is chorus and how does it work?

Answer 10

similar to flange except delay time is longer (20-30ms)

• feedback and depth should be low
• can also be created by modulating the pitch of a delayed signal

Question 11

How does a Leslie cabinet work?

Answer 11

rotating speaker creates a doppler effect

-two-horn rotator, only one is the speaker; the other horn is there for balance and does not produce sound

Question 12

How does the Doppler effect work?

Answer 12

• as the sound moves toward you the wave compressed, raising the pitch
• as the sound moves away the wave is stretched, lowering the pitch

Question 13

How do pitch processors work?

Answer 13

pitch processor compresses and stretches the wave through a constantly modulated delay time, but does not change the timing of the signal

• shortening delay raises the pitch
• lengthening delay lowers the pitch

Question 14

How does pitch correction (auto-tune, melodyne, etc.) work?

Answer 14

• data derived from an auto-correlation function of the input waveform is utilized to continuously determine the period of the waveform
• period of the waveform is then compared to desired period
• ratio of waveform period and desired period is computed to re-sample the waveform