1. ECE 492 Capstone Design: Multi-Effect Guitar
Group 4: Aaron Arnason, Byron Maroney, Edrick de Guzman

2. Motivation
As guitarists, we wanted to explore how audio effects are applied
Interesting to see what we could do with digital signal processing
We wanted to explore the analog domain by building our own amplifier

3. Project Overview The project consists of the following:
Digital Signal Processing
Hard-clipping (Distortion)
Delay Effect (Reverberation)
Amplifier

4. Audio Properties The audio core handles 44.1 kHz sample rate.
Since the DE2’s audio codec uses 16-bit sampling, the required bit-rate the DE2 audio codec’s output is determined by:
sampling frequency * bits per sample = bit rate
This calculation results to kbps (0.673 Mbps)

5. Distortion Effect Implementation Utilized hard clipping technique
Clipping is a form of distortion
Considered “hard” when clipping produces a flat-cutoff
Flat-cutoff results in a waveform closer to a squarewave
Square waves introduce higher frequency harmonics
Results in “fuzzy” or “dirty” audio effect

6. Distortion Effect Demo Challenges
Clipping the amplitude introduces power loss
Resulting in volume drop
Resolved by amplifying the sample after the clipping process

7. Reverberation Effect Implementation
The basic idea of reverb was first created using a variable delay with its signal fed back to create a series of delays that fade out over time
Feedback gain must be less than 1

8. Reverberation Effect Demo Challenges
Comb Filter as a side-effect
Required a big enough space of memory (interfacing with off-chip memory)
 Frequency cancellations that can mimic room effects, but can also yield ringing and instability

9. Amplifier Implementation Using the LM384N as the amplifier IC
The amplifier`s gain is internally fixed at 34 dB
Which equates to voltage gain 50 times input signal
Designed to boost signal coming from the DE2
Operational voltage between volts DC.
Potentiometer used for volume control
Cost is around $4.00 w/o speakers.

10. Amplifier
Demo
Challenges
Heating issue
Clipping issue

11. Components List Altera DE2 Amplifier Electric Guitar Nios II Processor
DSP
Wolfson WM8731 Audio CODEC
Amplifier
LM384N IC Chip
Visaton FRS 7 W – 8 ohm speakers
Electric Guitar

12. Optional Features Guitar Tuner Live Streaming Wireless Playability
More Effects:
Chorus
Flanger
Infinity Mirror (Visualizer) [1] - t_infinity_mirro.jpg

13. Questions