1. EE 445S Real-Time Digital Signal Processing Lab Spring 2017
Lab 7 Guitar Special Effects
Chao Jia & Sam Kanawati

2. Outline Comb filters Allpass filters Notch filters
Special effects with filters
Other effects

3. Comb filters
In signal processing, a comb filter adds a delayed version of a signal to itself, causing constructive and destructive interference. The frequency response of a comb filter consists of a series of regularly spaced notches, giving the appearance of a comb.
When two loudspeakers are playing the same signal at different distances from the listener, there is a comb filtering effect on the signal. Listeners hear a mixture of direct sound and delayed reflected sound. A comb filter is created where the two combine at the listener

4. Comb filters
FIR comb filter (single echo)
Number of stopbands is R/2

5. Comb filters
IIR comb filter (multiple echoes)

6. Allpass filters

7. Notch filters

8. Some special effects Echo FIR or IIR comb filters Delay > 100ms
Flanging
FIR comb filter with (periodically) varying delay
Delay between 1ms and 10ms

9. Some special effects Chorus Several independent comb filters

10. Some special effects Reverb Mimic a enclosed space (lots of echoes)

11. Other effects
Special effects can also be generated by altering the amplitude of the signal.
Tremolo
Repetitive up/down variation in the volume
Fuzz
Intentionally introduced distortion like clipping