Transcript Guitar Effects Processor

Guitar Effects Processor
Preliminary Design Review
September 9th, 2003
Groups Members:
Adam Bernstein
Hosam Ghaith
Jasenko Alagic
Matthew Iyer
Yousef Alyousef
Goals
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Provide a guitar effects generator
that
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Has a user friendly interface
Takes input from standard audio source
Produces output to standard amplifiers
Employs a modular design
Produces real-time output
Can be programmed by user
Produces reasonably good audio quality
Baseline Objectives
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Working CPU (microcontroller, memory,
etc.)
Common interface between controller and
all effects
Minimum of two working audio effects
User interface
Ability to program combinations/duration
of effects
Ability to adjust properties of effects (such
as intensity)
Block Diagram
Digital Control System
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Live adjustments
Effect programming
Effect driver
Live Adjustments
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PC and/or keypad/button interface
Buttons turn effects on/off, control
real-time parameters, and run
programs.
Extension – Ideally, analog controls
such as light (photo-resistor), levers,
and knobs will be provided to the
user. These analog controls can be
mapped to any desired effect.
Effect Programming
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ASCII text file can written to program the
effects generator
• Controls ramp/sweep of different effects
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Program A sweeps Distortion effect from 0-100
percent intensity in span of 5 seconds.
• Program pre-set state of effects
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State A loads 50% Distortion, 20% Tremelo, and
80% Wah
• Map buttons to functions
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Example: Button1 will trigger Program A, Knob1
controls intensity of Effect3, Button2 loads State A,
and so on…
Effect Programming
Sample ASCII file:
state 0 : 0 128 1 64
[state 0] : [effect 0 50%] [effect 1 25%]
program 0 : sweep 0 128 255 2000
[program 0] : [effect 0] [50%-100%] [2000
milliseconds]
knob 0 : 1 0 3
[knob 0] : [map to effect 1] [bits 0-3]
Extension: GUI application that helps
user write programs.
Effect Driver
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Sends control commands to
individual effects
• Support for 2n effect modules, where n
is the number of address bits
• k-bit messages sent on data bus
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Commands customized to control
parameters of each effect.
Example: Distortion
Diagram of Effect Driver
SERIAL
PORT
KEYPAD
RAM
EPROM
RESET
HC11 MICROPROCESSOR
CLOCK
FPGA
Mixed-Signal Interface Block
Diagram
DIP SWITCH
ADDRESS ID
3 BIT ASSIGNED ID
3 BIT ADDRESS BUS
3 BIT
LOGICAL
AND GATE
(Implemented in FPGA)
LATCH ENABLE
MIXED
SIGNAL
INTERFACE
LATCH
DATA BUS
Mixed Signal Interface
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Digital to Analog (D/A) conversion
methods
• Standard D/A converters translating
an array of digital bits into a bias
voltage
• Digitally controlled components
Digitally Controlled Components
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Determine the components in each
individual circuit that have the
largest impact on the intensity of the
effect
Devise specific interface scheme
between data bits and analog
component value
Continuously update component
value through interface scheme as
data bits are passed on the bus
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Xicor X9111
Digitally Controlled
Potentiometer
Turns on/off a
series of ~1000
gates moving a
“Wiper Arm” up
and down the
potentiometer
altering the
effective
resistance
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Xicor X90100
Digitally
Controlled
Capacitor
Turns on/off
numerous
capacitors in
parallel
increasing and
decreasing the
effective
capacitance
Analog Signal
Processing
Block Diagram of Signal
Processing Circuits
MIXED SIGNAL
INTERFACE
INPUT
SIGNAL
SIGNAL
CONDITIONING
CIRCUIT
SWITCHING
MECHANISM
SIGNAL PROCESSING
CIRCUIT
METAL STRUCTURE
LOW PASS FILTER
OUTPUT
SIGNAL
Requirements for Effect Circuits
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Input over-voltage protection
Ability to operate with DC power supply
Switch that turns on the effect or bypasses it
High input impedance unity-gain buffer to match the high
output impedance of a guitar
Low pass filter to compensate for the high harmonics added
in the effects stages
An output buffer to provide a low output impedance
A level control allowing the adjustment of effect intensity
When bypassed, the effect is shorted without degradation
of signal
LED indicating if the effect is on or off
Metal shield enclosing the circuit to eliminate noise
interference
Effect Circuits
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Distortion
Wah
Other effects can be implemented if
time permits
Distortion Effect Overview
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Distortion can be produced by clipping and/or
compressing a sound wave. There two kinds of
distortion:
• Harmonic: more ‘musical’
• Intermodulation: disturbing to the human ear
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Smooth edged clipping (soft clipping) produces
more harmonic distortion than sharp edged
clipping (hard clipping)
Objective:
• maximize the harmonic distortion
• reduce intermodulation distortion.
Hard vs. Soft Clipping
Wah Effect Overview
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Mimics the sound of the word ‘Wah’.
3 ways to control:
• Button
• Program (Auto-wah)
• Photoresistor
Wah Effect Implementation
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The main component is a simple
resonator
The resonator acts as a band-pass
filter
The center frequency and resonance
(Q-factor) can be adjusted by the
user.
Wah Effect
Order of Effects
1.
2.
3.
4.
5.
6.
Volume
Distortion
Tone controls
Small time delays and Phasers
Longer time delays - chorus
Reverb and echo, etc.
Courtesy of: http://www.geofex.com/effxfaq/fxorder.htm
Extensions
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Extra effects
Equalizer/Tone Control
Computer screen display
Ability to program the order in which
effects are applied
Superposition of different signals
Risks/Contingency Plan
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Noise resulting from analog signal
processing
• Use low pass filters and metal structures
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Interfacing with Mixed-Signal
components
• Add additional effect-side control
• Use standard D/A converters instead of
programmable components
Return on Investment
Investment/Return
Items
Labor
Parts
Cost of the Unit
Profit on the unit w/o
Labor
Units to break even
Amount
5 EE’s * 225 hrs/EE *
20 $/hr = $22,500
$30/unit
$100
$70
321
Division of Labor
Tasks:
Analog Signal
Processing
Mixed-Signal
Interface
Microprocessor
Done by:
Adam, Jasenko and
Yousef
Adam, Jasenko, and
Hosam
Matthew, Yousef, Hosam
Systems
Integration
Testing and
Quality
Assurance
Everybody
Everybody
Schedule
Questions?