Guitar Effects Processor Preliminary Design Review September 9th, 2003

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Guitar Effects ProcessorPreliminary Design
ReviewSeptember 9th, 2003

• Groups Members
• Adam Bernstein
• Hosam Ghaith
• Jasenko Alagic
• Matthew Iyer
• Yousef Alyousef

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Goals

• Provide a guitar effects generator that
• 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

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Baseline Objectives

• 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)

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Block Diagram
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Digital Control System

• Live adjustments
• Effect programming
• Effect driver

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Live Adjustments

• 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.

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Effect Programming

• ASCII text file can written to program the
  effects generator
• Controls ramp/sweep of different effects
• Program A sweeps Distortion effect from 0-100
  percent intensity in span of 5 seconds.
• Program pre-set state of effects
• State A loads 50 Distortion, 20 Tremelo, and
  80 Wah
• Map buttons to functions
• Example Button1 will trigger Program A, Knob1
  controls intensity of Effect3, Button2 loads
  State A, and so on

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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.

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Effect Driver

• 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
• Commands customized to control parameters of each
  effect.
• Example Distortion

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Diagram of Effect Driver
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Mixed-Signal Interface Block Diagram
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Mixed Signal Interface

• Digital to Analog (D/A) conversion methods
• Standard D/A converters translating an array of
  digital bits into a bias voltage
• Digitally controlled components

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Digitally Controlled Components

• 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

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Analog Signal Processing
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Block Diagram of Signal Processing Circuits
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Requirements for Effect Circuits

• 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

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Effect Circuits

• Distortion
• Wah
• Other effects can be implemented if time permits

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Distortion Effect Overview

• 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
• Smooth edged clipping (soft clipping) produces
  more harmonic distortion than sharp edged
  clipping (hard clipping)
• Objective
• maximize the harmonic distortion
• reduce intermodulation distortion.

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Hard vs. Soft Clipping
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Wah Effect Overview

• Mimics the sound of the word Wah.
• 3 ways to control
• Button
• Program (Auto-wah)
• Photoresistor

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Wah Effect Implementation

• 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.

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Wah Effect
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Order of Effects

• 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

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Extensions

• Extra effects
• Equalizer/Tone Control
• Computer screen display
• Ability to program the order in which effects are
  applied
• Superposition of different signals

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Risks/Contingency Plan

• Noise resulting from analog signal processing
• Use low pass filters and metal structures
• Interfacing with Mixed-Signal components
• Add additional effect-side control
• Use standard D/A converters instead of
  programmable components

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Return on Investment
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Division of Labor
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Schedule
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Questions?