Electronic Music Composition Unit 2 ReviewSound and Audio Fundamentals

What is Sound?

• Sound is a vibration that travels through a medium (air, water, solids) as a mechanical wave
• Occurs when an object vibrates, creating a series of compressions and rarefactions in the surrounding medium
• Compressions are areas of high pressure where molecules are pushed together
• Rarefactions are areas of low pressure where molecules are spread apart
• Human ear perceives these pressure variations as sound when they reach the eardrum
• Characteristics of a sound depend on the properties of the vibrating object and the medium through which the sound waves travel
• Sound requires a medium to propagate; it cannot travel through a vacuum
• Speed of sound varies depending on the medium (fastest in solids, slower in liquids, slowest in gases)

Physics of Sound Waves

• Sound waves are longitudinal waves, meaning the direction of vibration is parallel to the direction of travel
• Wavelength is the distance between two consecutive compressions or rarefactions
• Frequency is the number of wavelengths that pass a fixed point per second, measured in Hertz (Hz)
• Amplitude is the maximum displacement of a sound wave from its resting position, determining the loudness of the sound
• Sound intensity is the amount of energy transmitted by a sound wave per unit area, measured in decibels (dB)
• Inverse square law states that sound intensity decreases with the square of the distance from the source
• Reflection occurs when a sound wave encounters a surface and bounces back, leading to echoes and reverberation
• Absorption happens when sound energy is converted into heat as it passes through a medium or strikes a surface
• Refraction is the bending of sound waves as they pass through mediums of different densities
• Diffraction allows sound waves to bend around obstacles and spread out after passing through an opening

Frequency, Amplitude, and Timbre

• Frequency determines the pitch of a sound
  • Higher frequencies produce higher-pitched sounds, while lower frequencies produce lower-pitched sounds
  • Human hearing range is approximately 20 Hz to 20,000 Hz (20 kHz)
• Amplitude relates to the perceived loudness of a sound
  • Higher amplitudes result in louder sounds, while lower amplitudes result in quieter sounds
  • Measured in decibels (dB), a logarithmic scale
    • 0 dB is the threshold of human hearing, and 120 dB is the threshold of pain
• Timbre is the unique quality or character of a sound that distinguishes it from other sounds with the same pitch and loudness
  • Determined by the harmonics present in the sound and their relative amplitudes
  • Allows us to differentiate between different instruments playing the same note
• Envelope describes how a sound's amplitude changes over time, consisting of four stages: Attack, Decay, Sustain, and Release (ADSR)
• Harmonics are integer multiples of the fundamental frequency that contribute to a sound's timbre
• Overtones are any frequencies present in a sound that are higher than the fundamental frequency, including harmonics and non-integer multiples

Digital Audio Basics

• Analog audio signals are continuous and can take on any value within a given range
• Digital audio is a representation of analog audio signals using binary numbers
• Analog-to-digital conversion (ADC) is the process of converting an analog audio signal into a digital signal
  • Sampling is the process of measuring the amplitude of an analog signal at regular intervals
  • Quantization is the process of assigning a discrete value to each sample based on its amplitude
• Digital-to-analog conversion (DAC) is the process of converting a digital audio signal back into an analog signal for playback
• Nyquist-Shannon sampling theorem states that the sampling rate must be at least twice the highest frequency component of the analog signal to accurately represent it
• Bit depth determines the resolution and dynamic range of a digital audio signal
  • Higher bit depths allow for more precise representation of amplitude values and greater dynamic range
• Dithering is the process of adding low-level noise to a digital audio signal to reduce quantization errors and improve perceived sound quality
• Jitter is the undesired variation in the timing of digital audio samples, which can lead to distortion and degradation of sound quality

Audio Formats and Compression

• Uncompressed audio formats store audio data without any loss of quality, but result in larger file sizes (WAV, AIFF)
• Lossless compression reduces file size without losing any audio data, allowing for perfect reconstruction of the original signal (FLAC, ALAC)
• Lossy compression achieves smaller file sizes by removing audio data that is considered less perceptible, resulting in some loss of quality (MP3, AAC, OGG)
  • Psychoacoustic modeling is used to identify and remove audio data that is less likely to be perceived by the human ear
• Bit rate is the amount of data used to represent one second of audio, measured in bits per second (bps) or kilobits per second (kbps)
  • Higher bit rates generally result in better audio quality but larger file sizes
• Variable bit rate (VBR) encoding adjusts the bit rate dynamically based on the complexity of the audio signal, allocating more bits to complex sections and fewer bits to simpler sections
• Constant bit rate (CBR) encoding uses the same bit rate throughout the entire audio file, regardless of the complexity of the audio signal
• Container formats (MP4, MKV, OGG) can store multiple types of data, such as audio, video, and metadata, in a single file

Sampling and Bit Depth

• Sampling is the process of converting a continuous analog audio signal into a series of discrete digital values
• Sample rate is the number of samples taken per second, measured in Hertz (Hz) or kilohertz (kHz)
  • Higher sample rates capture higher frequencies and result in better audio quality, but also larger file sizes
  • Common sample rates: 44.1 kHz (CD quality), 48 kHz (professional audio), 96 kHz and 192 kHz (high-resolution audio)
• Bit depth is the number of bits used to represent each sample
  • Higher bit depths allow for more precise representation of amplitude values and greater dynamic range
  • Common bit depths: 16-bit (CD quality), 24-bit (professional audio), 32-bit (high-resolution audio)
• Quantization is the process of assigning a discrete value to each sample based on its amplitude
  • Quantization error occurs when the actual amplitude of a sample does not exactly match any of the available discrete values
• Dithering is the process of adding low-level noise to a digital audio signal to reduce quantization errors and improve perceived sound quality
• Oversampling is a technique used during analog-to-digital conversion to sample the audio signal at a higher rate than the desired output sample rate, which helps to reduce aliasing and improve signal-to-noise ratio
• Decimation is the process of reducing the sample rate of a digital audio signal by removing samples, often used in conjunction with oversampling to achieve the desired output sample rate

Essential Audio Equipment

• Microphones convert acoustic energy (sound waves) into electrical energy (audio signals)
  • Dynamic microphones use a moving coil attached to a diaphragm to generate an electrical signal, are durable and versatile
  • Condenser microphones use a thin, electrically-charged diaphragm to capture sound, are sensitive and ideal for recording detailed audio
  • Ribbon microphones use a thin metal ribbon suspended in a magnetic field to capture sound, have a warm, natural tone
• Audio interfaces convert analog audio signals from microphones and instruments into digital signals for recording, and convert digital signals back to analog for monitoring and playback
  • Microphone preamps amplify low-level signals from microphones to line level for further processing or recording
  • Analog-to-digital converters (ADC) and digital-to-analog converters (DAC) handle the conversion between analog and digital audio signals
• Mixers combine and process multiple audio signals, allowing for level adjustment, panning, equalization (EQ), and effects processing
  • Analog mixers use physical circuits to process audio signals
  • Digital mixers use digital signal processing (DSP) to manipulate audio signals
• Studio monitors are loudspeakers designed for accurate, uncolored reproduction of audio in a studio environment
  • Near-field monitors are placed close to the listener and are designed for critical listening and mixing
  • Headphones allow for private monitoring and can be used for recording and mixing
• Audio cables and connectors are used to route audio signals between devices
  • Balanced cables (XLR, TRS) use three conductors to reduce noise and interference over long cable runs
  • Unbalanced cables (TS, RCA) use two conductors and are more susceptible to noise, but are suitable for shorter cable runs
• Digital Audio Workstations (DAWs) are software applications used for recording, editing, mixing, and producing audio
  • Examples include Ableton Live, FL Studio, Logic Pro, Pro Tools, and Studio One

Sound Synthesis Fundamentals

• Sound synthesis is the process of generating audio signals using electronic or digital means
• Additive synthesis creates complex sounds by combining simple waveforms (sine, triangle, square, sawtooth) at different frequencies and amplitudes
  • Each waveform represents a harmonic or partial of the overall sound
  • Fourier synthesis is a type of additive synthesis based on the Fourier series, which states that any periodic waveform can be decomposed into a sum of sinusoidal waves
• Subtractive synthesis starts with a harmonically rich waveform (e.g., square or sawtooth) and shapes it using filters, envelopes, and modulation
  • Low-pass, high-pass, and band-pass filters remove or attenuate frequencies above, below, or outside a specified cutoff frequency
  • ADSR envelopes shape the amplitude, pitch, or filter cutoff over time
• Wavetable synthesis uses a table of pre-recorded or generated waveforms to create evolving sounds
  • Interpolation between waveforms allows for smooth transitions and creation of new timbres
• Frequency modulation (FM) synthesis creates complex timbres by using one oscillator (the modulator) to modulate the frequency of another oscillator (the carrier)
  • FM synthesis is known for creating metallic, bell-like, and percussive sounds
• Granular synthesis generates sounds by combining short snippets of audio called grains
  • Grains can be played back at different speeds, pitches, and positions, allowing for the creation of unique textures and soundscapes
• Physical modeling synthesis aims to recreate the sound of acoustic instruments by simulating their physical properties and behavior
  • Techniques include mass-spring models, finite element methods, and digital waveguides
• Modular synthesis uses interconnected hardware or software modules to create and manipulate sounds
  • Modules can include oscillators, filters, envelopes, LFOs (low-frequency oscillators), and effects
  • Patching between modules determines the flow of audio and control signals