1. Basic Digital Audio Effects
R.C. Maher
EELE 217

2. Digital Delay One sample after another is written into memory… Input
RAM (memory)
Output
…and read out later. Delay is the number of samples between write pointer and read pointer.

3. Recirculating Delay: Echo
Delayed output is attenuated and added back in with the input samples.
Input + a
RAM (memory)
Output

4. Recirculating Delay (cont.)
Frequency response of system
A “comb” filter. Frequency at peaks depends on delay length.

5. Time-Varying Delay: Flanger
Feed forward: delayed output is added back in with the input samples. Delay varies up and down as a function of time.
Input
Output + a
RAM (memory)

6. Reverb Simulation
Plan: use parallel recirculating delay lines with incommensurate delays +
Delay Line (z-N1) + k1 +
Delay Line (z-N2) k2

7. Other Improvements Cascade of all pass recirculators -k+
Delay Line (z-N) +
N poles and zeroes equally spaced around circle
(pole radius k1/N, zero radius k-1/N) k

8. Gain Control Gain control framework
c[n] can be |x[n]|, envelope of x[n], RMS value of x[n], etc.
Level detector typically has attack and release time constants
Level Detector
Gain
Controller
x[n]
c[n]
y[n]=G[n] • x[n]
G[n]