Digital Audio and Acoustics for the Creative Arts

Designed for introductory courses in electronic music and multimedia, Digital Audio and Acoustics for the Creative Arts presents the fundamental concepts of musical acoustics, psychoacoustics, electronics, digital audio, audio recording, and communication among devices via the Musical Instrument Digital Interface (MIDI) and Open Sound Control (OSC).

Mark Ballora is Associate Professor of Music Technology at Penn State University.

Acknowledgments
Introduction

1. Basic Acoustics
The Nature of Sound Events
Wave Propagation
Simple Harmonic Motion
Characteristics of Waves
Refraction and Reflection
Superposition
Standing Waves, Resonant Frequencies, and Harmonics
Sympathetic Resonance
Phase and Waveshape
Speed and Velocity
Frequencies of Strings and Echoes
String Frequencies
Echo Rate
Suggested Exercises

2. Music and Acoustics
Properties of Musical Sound
What Is the Difference Between Music and Noise?
Frequency/Pitch
Frequency and Wavelength
Doppler Shift
Frequency Is Fixed and Precise, Pitch Is Flexible and by Convention
Human Pitch Perception is Logarithmic
Loudness
Power
Complications in Measuring Acoustic Power Levels
The Decibel Scale
Definition of the Decibel
Intensity
Pressure
Relationship of Intensity to Pressure
Root Mean Square
Pressure and Decibels
Understanding "Negative" Decibels
Timbre
Modes of Vibration
The Fourier Analysis
Spectral Plots
Limitations of the Fourier Transform
The Harmonic Series and Intonation
Pitches Are Just Ratios
Harmonics in Performance
A Partial by Any Other Name...
Formants
Timbre: To Be Continued...
Making Waves: Building Blocks of Sound Synthesis
Suggested Exercises

3. Perceptual Issues in Acoustics
What Is the Difference Between Consonance and Dissonance?
The Mystery of the Octave, and the Evolutionary Basis of Music
Perspectives on Consonance and Dissonance
Sound Spectra in Time
Localization of Natural Events
Interaural Time Delay (ITD)
Spectral Shadowing, or Interaural Level Delay (ILD)
Pinnae Filtering
Mismatches Between Measurement and Perception
Phase
Timbre
Loudness
Masking
Hearing Things That Aren't There
--Second-order Beats
--Binaural Beats
--The Missing Fundamental
--Difference Tones
The Physical Basis of Pitch Perception
Auditory Scene Analysis
Turn It Down!
Suggested Exercises

4. Fundamentals of Electricity
Static Electricity
Electricity = Electrons
From Parlor Tricks to Lightning Storms
Current, Voltage, Resistance, and Power
The Battery
Magnetism
Magnetism and Electrical Current
Magnetic Induction
Electromagnetic Resonance
Impedance
--Coils and AC: Inductance
--Capacitor Plates and AC: Capacitance
Impedance, Voltage, and Current
Controlling Current: From Vacuum Tubes to Microprocessors
Vacuum Tubes
Semiconductors
Electronics and Music
Telephone Communication
Vinyl Records
Tape
Radio Broadcasting
Studio Connections
Grounding
Audio Levels
Audio Cables and Impedance
Keeping a Squeeze on Current
Suggested Exercises

5. The Basics of Digital Audio
Historical Context
Digitizing Audio: The Big Picture
The Central Problem
Digital Conversion
Does Digital Sound as Good as Analog?
--Arguments for Analog
--Arguments for Digital
--So Where Does That Leave Us?
Characteristics of Digital Audio
Sampling Rate
The Sampling Rate of CD Audio and Its Origin
Sample Size
--Signal-to-Error Ratio
--Dither
Sample Size vs. Sampling Rate
Filtering
What Is Filtering?
Filter Types
--Lowpass Filter
--Highpass Filter
--Bandpass Filter
--Band-Reject Filter
--"Everything Is a Filter!"
The Digital Filtering Process
Feedforward vs. Feedback Filters
Lowpass Filters
Highpass Filters
Bandpass and Band-Reject Filters
Other Filter Characteristics
The Digital Recording and Playback Process
Recording
--Dither
--Lowpass(Antialiasing) Filter
--Sample and Hold
--Analog-to-Digital Converter (ADC)
--Multiplexer
--Error Correction
--Encoding
Playback
--Buffer
--Error Correction
--Digital-to-Analog Converter (DAC) and Sample and Hold
--Output Lowpass Filter
Suggested Exercises

6. Working with Digital Audio
Analysis and Processing
Spectral Representation
--0 Hz = Direct Current
--Spectra of Digital Signals
--The Fourier Transform Process
----Perspective One: Multiplication by Probe Signals
----Perspective Two: A Harmonic Coordinate System
----Perspective Three: Taking the Inner Product
----Perspective Four: Filter Bank
--The Fast Fourier Transform (FFT)
--Time Domain Localization vs. Spectral Resolution
----Segmenting the Signal: Short Time Fourier Transform and Window Functions
----Window Length and Spectral Resolution
----Window Functions
Convolution
--What Is It?
--Why Is Convolution Important?
----Time Domain Multiplication: Ring Modulation
----Time Domain Convolution: Filtering
----Finite Impulse Response (FIR) Filters and Infinite Impulse Response (IIR) Filters
----Spectral Shaping
Oversampling and Noise Shaping
Perceptual Coding
Psychoacoustics
Masking and Perceptual Coding
Encoding Techniques
Approaches to Improving Audio: Compress Content or Increase Resolution?
Storage Media
Compact Disc
--Retrieving Data
--The Form of the Data
CD Recorders
DVD
Super Audio CD (SACD)
DVD-Audio
High Definition Compatible Digital (HDCD)
Blu-ray
Hard-Disk Recording: The Convergence of Multimedia
Digital Workstations
Transferring Data Between Devices
Audio File Types
--NeXT/Sun
--AIFF
--SDII
--WAVE
--CAF
Video Streaming and Networked Music
Suggested Exercises

7. Acoustic Signatures: Room Acoustics, Microphones, and Loudspeakers
Room Acoustics
Direct and Reflected Sound
Large Performance Spaces
--Direct Sound
--Early Reflections
--Diffuse Reverberation
--Reverberation Radius
--Impulse Response
--Interaural Cross-Correlation (IACC)
--Types of Reflection: Specular and Diffuse
--Speech vs. Music
--Absorption
--Absorption and Sound Propagation
--Ideal Concert Hall Characteristics
Small Performance Spaces
--Room Modes
--Flutter Echo
--Comb Filtering
--Acoustic Treatment of Small Spaces
Microphones
Receptor Types
--Pressure
--Pressure Gradient (Velocity)
Transducer Types
--Dynamic (Electrodynamic, Electromagnetic, Ribbon, Moving Coil)
--Condenser (Capacitor)
Directionality
--Omnidirectional
--Bidirectional (Figure 8)
--First-Order Directional Microphones
--Standard Cardioid
--Subcardioid
--Supercardioid
--Hypercardioid
Variable Pattern Microphones
Directionality and Frequency Response
--Phase Drop-off
--Intensity Drop-off
Direct vs. Diffuse Sound Responses
Microphone Configurations
Recording Popular vs. Recording Classical
Time-of-Arrival Configurations
Intensity Configurations
--XY Microphone Configuration
--MS Microphone Configuration
Near-Coincident Configurations
--ORTF
--Spherical Stereo Microphones
Support (Accent) Microphones
Multi-Microphone Configuration for Recording Large Ensembles
Surround Recording Configurations
--INA 5
--The Fukada Tree
--OCT Surround
--Expansions of the Spherical Stereo Microphone
--Soundfield Microphone
Loudspeaker Technology
Suggested Exercises

8. Treating and Mixing Audio
Effects: An Introduction
Combining Effects
A Few Words on Word Length
Error and Word Length
Converting to Lower Word Sizes
Latency
Delay-Based Effects
Simple Delay
Multitap Delay
Feedback Delay
Building Blocks of Delay-Based Effects: Comb and All-pass Filters
Comb Filters
--Feedforward Comb Filter (Inverted Comb Filter)
--Feedback Comb Filter
All-pass Filters
Delay-Based Effects
Flanging
Chorusing
Phase Shifting
Reverberation
--Reverb Chamber (Echo Chamber)
--Spring Reverb
--Plate Reverb
--Digital Reverberation
--Convolution Reverb
Delayed Signals: A Matter of Interpolation
Spectral Effects
Ring/Amplitude Modulation
Channel Vocoder
Phase Vocoder
Dynamic Effects
Compressor/Limiter
Expander/Noise Gate
Companding
Normalization/Maximization
--Normalization
--Maximization
Mixing and Signal Flow
Channels
Level Meters
Phantom Power
Channel Insert
Equalization
Channel Fader
Mixer Buses
Mute/Solo Switches
Pan
Output Buses
Patchbay
Stereophony
Localization vs. Spaciousness
Simulated Localization in Audio Systems
Quadraphony
5.1 Surround Sound
Eight Channels and More
Ambisonics
Mastering
Suggested Exercises

9. Communication Among Devices
MIDI: The Big Picture
Connecting MIDI Synthesizers
MIDI Messages
Status Bytes and Data Bytes
Channel Voice Message Types
--Note Off
--Note On
--Polyphonic Key Pressure (Poly Aftertouch)
--Channel Key Pressure (Channel Aftertouch)
--Program Change
--Pitch Bend
--Control Change
System Exclusive Messages
--Start System Exclusive
--End System Exclusive (EOX)
MIDI Utility Programs
Additions to the MIDI Protocol
Standard MIDI Files (SMFs)
General MIDI
Karaoke Files
GS MIDI and XG MIDI
MIDI Show Control (MSC)
Just What Do You Mean By That?
Open Sound Control (OSC)
Remapping Values
DIY Device Development
Suggested Exercises

10. Digital Instruments
Hardware Instruments
Samplers
Synthesizers
Alternate MIDI Controllers
Software Instruments
MIDI-Based Software
--Sequencing Software
--Notation Software
--Editor/Librarian Software
Digital Audio-Based Instruments
--Digital Audio Workstation Software
--Softsynths and Sample Libraries
Sound Synthesis
Wavetables
Unit Generators and Signal Flow Charts
Additive Synthesis
Subtractive Synthesis
--Low Frequency Oscillator (LFO)
--Detune
--Pulse Width Modulation (PWM)
--Oscillator Sync
--Vowel Synthesis
Frequency/Phase Modulation
Nonlinear Waveshaping
Physical Modeling
Granular Synthesis
Algorithmic and Interactive Composition
Suggested Exercises

11. Tales from the Trenches: Survival Tips in Specific Contexts
Live Sound Mixing
Setting Up a Recording Studio
Room Coloration
Electrical Noise
Common-Sense Procedures
Cable Wrapping
Order of Operation
Scoring for Video
Networking Devices
Network Address Components
--Router
--IP (Internet Protocol) Address
--Subnet Mask
--Ports
Examples of Network Connections
--Mixer Console App
--Max/MSP and SuperCollider
--Lemur and SuperCollider
--MIDI over LAN
--Audio over LAN

Appendix 1: Geometric View of a Sine Wave
Phasors, Radians, and the Unit Circle
Sinusoidal Equation

Appendix 2: Plotting Sine Charts in a Spreadsheet
Creating a Basic Sine Wave Plot
Step One: Create a Series of 360 Values (from 0 to 359)
Step Two: Convert Degrees to Radians
Step Three: Create a Sine Wave
Step Four: Plot the Sine Values
Building on the Foundation
Change Amplitude, Frequency, and Initial Phase
Use Absolute Cell References
Use an Absolute Column Reference and a Relative Row Reference
Plot More Than One Sine Wave
Add the Separate Sine Waves to Create a Composite Sine Wave

Appendix 3: Overview of Logarithms
Exponents, Viewed from Another Angle
Property 1
Property 2
Property 3

Appendix 4: Representing Numbers
Numbers Are Power
Of What Value Power?
Numbers in Computers
The Binary Number System
Some Essential Terminology
The Hexadecimal Number System
Integers and Floating Points

Glossary
Bibliography