Unit
- Sound waves: Sound propagates as vibrations through a medium. Frequency determines pitch, measured in hertz (Hz). Human hearing typically ranges from 20 Hz to 20,000 Hz. Amplitude determines loudness, measured in decibels (dB). Dynamic range in audio environments spans about 96 dB for 16-bit systems.
- Timbre and harmonics: Timbre differentiates sounds of same pitch and loudness. Harmonics are integer multiples of the fundamental frequency. A 440 Hz note with harmonics at 880 Hz, 1320 Hz creates a rich tone compared to a pure sine wave.
- Phase and interference: Phase describes the timing relationship between waves. Constructive interference increases amplitude when waves align. Destructive interference cancels sound when waves are exactly opposite. Comb filtering occurs when delayed copies of a signal combine.
- Envelope and transients: Every sound has an amplitude envelope: attack, decay, sustain, release (ADSR). The attack transient defines initial impact, critical for percussive sounds. Fast attacks (under 10 ms) signal immediate events like impacts.
- Psychoacoustic principles: The ear uses critical bands for frequency analysis. Masking occurs when louder sounds obscure quieter ones at nearby frequencies. Precedence effect localizes sound from the first arriving wavefront.
- Sound localization cues: Interaural time difference (ITD) for low frequencies below 800 Hz. Interaural level difference (ILD) for high frequencies. Head-related transfer function (HRTF) filters sound based on ear shape and head shadow.
- Temporal integration: The ear integrates energy over 20-200 ms windows. Short sounds below this window are perceived quieter even if peak level is high. This explains why clicks need higher peak levels than sustained tones.
- Frequency spectrum visualization: Spectrograms display frequency over time with amplitude as color. Sonograms serve as blueprints for sound designers to identify harmonics, noise, and transients in audio clips.
- Acoustic impedance and transmission: Acoustic impedance describes how sound energy travels between different media, calculated as density times speed of sound. Impedance mismatch causes reflection, which is why sound passes poorly from air to water. Understanding this helps design effective soundproofing and microphone placement.
- Standing waves and room modes: When sound reflects between parallel surfaces, standing waves form at specific frequencies. Room modes cause uneven bass response, with nodes and antinodes at different positions. Sound designers use bass traps and diffusers to minimize these effects for accurate monitoring.
- Resonance and filter design: Every physical system has natural resonant frequencies that amplify sound. In sound design, resonant filters boost specific harmonics, creating musical tones or feedback effects. A resonant low-pass filter with high Q factor can produce a whistling or ringing quality.
Design Principle
Principle: Frequency Separation for Clarity
Definition: Assign distinct frequency ranges to each sound element in a mix to reduce masking. Ensure overlapping sounds have complementary spectral content so each remains intelligible.
Application: When designing a sci-fi weapon sound, allocate the low thump to 60-200 Hz, the mid buzz to 400-1200 Hz, and the high sparkle to 4-8 kHz. Use EQ to carve space, leaving each harmonic band prominent.
Quick Revision
- Sound is defined by frequency (pitch), amplitude (loudness), and timbre (harmonic content).
- The ADSR envelope (attack, decay, sustain, release) shapes a sound's dynamic evolution.
- Psychoacoustic phenomena such as masking and the precedence effect guide placement of sounds in a mix.
- Frequency spectrum analysis using spectrograms helps identify and separate overlapping sound components.