IAT 340: Sound Design Lecture Notes
IAT 340: Sound Design
Instructor
Philippe Pasquier
Email: pasquier@sfu.ca
Summary of Previous Weeks
Fundamentals of Acoustics and Digital Audio Processing:
Sound: its production, propagation, and perception
Sonic waves representation and properties:
Time vs frequency domain (waveform vs spectrogram)
Sound digitalization:
ADC (Analog to Digital Converter) and DAC (Digital to Analog Converter)
Concepts of sampling rate and bit depth
Aliasing and quantization noise
Audio file formats
Audio in and out:
Microphones
Mixing consoles or soundboards
Loudspeakers
Digitalizing Sound
Overview of the audio digital recording and playback chain.
Waveform
Definition:
A waveform is a graphical representation of a sound wave, depicting its amplitude over time.
Frequency Spectrum Through Time
Example: Waveform of the onset of an acoustic bass pluck
Visual representation of amplitude vs time
Spectrogram (Long-window):
Shows frequency (in Hz) vs time, providing insight into the frequency spectrum.
Sound β Frequency Spectrum
Spectrogram:
Visual representation of the frequency spectrum of sound.
Fourier Transform:
Used for spectral analysis, converting time-domain waveform into frequency-domain spectrum.
Harmonic Sound
Example: Frequency spectrum of a trumpet playing an A4 note
Fundamental Frequency (F): Represents the basic pitch
Harmonics: Frequencies that are integer multiples of the fundamental frequency, e.g., 2F, 3F, etc.
Inharmonic Sound
Example: Frequency spectrum of a metal chime
Fundamental Frequency (F): The primary frequency present in the sound
Overtones: Frequencies present that do not form a harmonic series.
Noise
Definition: Random signal; represents the extreme case of aperiodicity.
Types of Noise:
Different colors of noise characterized by power distribution in their frequency spectrum.
White Noise: Characterized by a flat spectrum across all frequencies.
Electric Hum:
Special case of noise caused by electromagnetic or electric interference, often related to ground loop problems
Example: 60Hz hum from shared ground connections.
Psychoacoustic: Human Hearing
Representation of sound pressure level (SPL) in decibels (dB) across frequency (Hz)
Pain threshold, audible range, and orchestral/vocal ranges annotated on the graph.
Outline of Today's Lecture
Introduction
Audio editing: tips
Various operations and effects
Basics of mastering
Next week: Active listening session
Audio Editing History
Audio Editing:
Process of altering recorded sound directly on the recording medium (analog) or in RAM (digital).
Development during the mid-20th century included the use of straight razors and splicing tape for magnetic tape.
Scrubbing: Technique of rocking back and forth on tape to locate specific sounds.
First Digital Sound Editor:
Sound Designer by Digidesign achieved early industry dominance.
Audacity: Currently the most feature-rich free software audio editor.
Reaper: Noted for excellent sound editing tools.
Important Concepts of Audio Editing
True silence does not exist; thus, all systems exhibit some level of noise.
Noise Floor:
The level at which the softest sound can be perceived.
Signals under this level are masked by background noise.
Dynamic Range:
Difference between peak amplitude and the softest signal value, expressed in dB.
Signal-to-Noise Ratio (SNR): Dynamic range between loudest signal and noise floor, also expressed in dB.
Dynamic Range
Description:
Ratio of the loudest undistorted sound to the quietest sound level or noise.
Example: Calculation of dynamic range given SPL levels:
Digital vs Analog Dynamic Ranges:
Maximum dynamic range for digital audio determined by bit depth.
Examples:
16-bit PCM: 98 dB dynamic range
Magnetic tape: ~55 dB dynamic range
Vinyl disk: ~65 dB dynamic range
Quantization Noise:
A specific type of noise that appears in digital systems due to half-bit amplitude noise.
Best practices for utilizing dynamic range include:
Recording at appropriate levels to maximize clarity.
Bit Depth
Definition: Levels to which audio energy can be approximated over time.
With 16-bit audio: 65,536 levels (96 dB)
With 24-bit audio: 16,777,216 levels (144 dB).
Benefits include:
Lower chance of struggling above the noise floor
More headroom for recording
Avoidance of truncating peaks, leading to clearer instrumentation and vocals
Audio Editing Operations
Volume/Gain/Amplitude Modulation:
Volume is adjustable based on how it corresponds to sound wave amplitude and perceived loudness.
Cutting:
Processes include fade in/out and zero crossing adjustments.
Normalization:
Volume adjustment to peak amplitude at 0 dB.
Compression/Expansion:
Control of dynamics through varying gain based on input sound levels.
Effects:
Types include distortion, phaser, flanger, chorus, time shifter, filters, equalization, and pitch shifter.
Sound Editing: Volume
Volume Control Operations:
The volume can be adjusted through multiplication by a constant factor.
Expressed in dB for convenience.
Continuous Waveforms:
Importance of continuity in waveforms; discontinuities are regarded as glitches (clicks, pops).
Zero Crossing Rule:
Always apply fade in/out to avoid glitches at start/end of samples, generally around 5ms.
Amplitude Modulation:
Cases with varying volume over time; includes volume automation such as tremolo effects.
Normalization: Adjusting peak amplitude up to 0 dB, ensuring no clipping occurs.
Compression, Expansion, and Limiting
Overview:
These processes manipulate dynamic range by adjusting gain based on sound level inputs.
Compressor:
Reduces dynamic range by lowering high volume signals while raising overall levels.
Commonly used to achieve even volume levels in vocals and music.
Expander:
Increases dynamic range by lowering quiet signals; useful for noise reduction.
Limiter:
A specialized compressor that reduces dynamic range drastically to prevent overdriving.
Dynamic Range Manipulation
Noise Gate:
Removes signals below a certain threshold, beneficial for cleaning up silent breaks in recordings.
Reversing a Sound
Process:
Inverts the order of sample lists to create a reverse playback effect.
Sound Effects
Delay:
Adds a delayed copy of the sound to the signal, can be a single delay or multi-tap effects.
Chorus Effect:
Creates the illusion of multiple sound sources by modulating pitch and delaying the input signal.
Flanger, Phaser, and Wah-wah:
Flanging and phasing create sweeping effects via modulated delays.
Wah-wah effects are characterized by band-pass filtering, used prominently in electric guitar.
Time Stretching
Definition:
Changes duration of sound without altering pitch; useful for fitting sounds to visual media or altering vocal speed for clarity.
Frequency Domain Effects
Types of Filters:
Lowpass, highpass, bandpass, and bandreject filters alter frequency envelopes and are crucial in EQ.
Equalization (EQ)
Definition:
Process of adjusting frequency response of sound involving filters and gain controls.
Pitch Shift and Pitch Bend
Pitch Shift Effect:
Alters pitch with or without retaining duration; fundamental for mixing clips with differing pitches.
Pitch Bend:
Changes pitch and duration for adjusting beat synchronization in DJing.
Editing and Mastering
Editing Phase:
Involves loading sounds, cutting, sequencing, and adjusting levels or effects.
Mastering Phase:
Covers noise reduction, stereo adjustments, ambience, final track levels, dynamic processes, and peak limiting.
Bouncing:
Selecting export formats and timeline portions for exporting final outputs.
Loudness War
Explanation:
A phenomenon where sound volume is pushed to extreme levels, often sacrificing dynamic range for perceived loudness.
Acoustic Ecology
Builds on active listening, aims to document and analyze soundscapes to promote awareness and critical thinking.
History:
Initiated by R. Murray Schafer at SFU with the World Soundscape Project.