Unit
- Sound waves: travel as pressure variations through air, water, or solid materials, compressing and rarefying molecules in a repeating pattern that our ears convert into perceived audio. Every engineering decision starts with understanding that sound is mechanical energy, not an abstract digital concept, even when working entirely inside a computer.
- Frequency: measures how many complete wave cycles occur per second, expressed in Hertz (Hz). Low frequencies below 250 Hz create the sensation of bass and weight, midrange frequencies between 250 Hz and 4000 Hz carry most vocal and instrumental clarity, and high frequencies above 4000 Hz deliver air, sparkle, and detail.
- Amplitude: represents the intensity or loudness of a sound wave, determined by how far air molecules move from their resting position. Engineers measure amplitude in decibels (dB), a logarithmic scale that matches human hearing perception more accurately than a linear scale would.
- Wavelength: describes the physical distance a sound wave travels during one complete cycle, calculated by dividing the speed of sound by frequency. Low frequencies have long wavelengths, sometimes exceeding 10 meters, which explains why bass frequencies behave unpredictably in small rooms and require careful acoustic treatment.
- Phase: refers to the position of a wave cycle at a specific point in time, measured in degrees from 0 to 360. When two identical waves align perfectly, they reinforce each other; when they are 180 degrees out of phase, they cancel each other out, a phenomenon engineers must manage during multi-microphone recording.
- Harmonics: are additional frequencies that occur at whole-number multiples of a fundamental frequency, giving instruments their unique timbre. A guitar string vibrating at 440 Hz also produces energy at 880 Hz, 1320 Hz, and beyond, and the relative strength of these harmonics is what distinguishes a guitar from a piano playing the same note.
- Speed of sound: travels at approximately 343 meters per second through air at room temperature, though this figure changes with humidity and temperature. This speed matters directly when calculating room dimensions, delay times, and the physical distance between microphones and sound sources during recording sessions.
- Sound pressure level: quantifies loudness relative to the threshold of human hearing, using a reference point of 20 micropascals as 0 dB SPL. Understanding this scale helps engineers set safe monitoring levels and recognize that a 10 dB increase represents a perceived doubling of loudness, not merely a small incremental change.
Design Principle
Principle: Frequency-Informed Listening
Definition: Training the ear to associate specific frequency ranges with physical sensations and instrument characteristics before relying on visual meters or spectrum analyzers.
Application: When evaluating a mix, an engineer should first ask whether the low end feels appropriately weighted between 60 Hz and 120 Hz, whether vocal presence sits clearly between 2000 Hz and 5000 Hz, and whether harshness appears between 3000 Hz and 6000 Hz, forming judgments by ear before confirming with analysis tools.
Quick Revision
- Sound is mechanical energy traveling as pressure waves through a medium.
- Frequency determines pitch perception and is measured in Hertz.
- Amplitude corresponds to loudness and is measured on the decibel scale.
- Phase relationships between waves can cause reinforcement or cancellation.
- Harmonics give instruments their distinct timbre beyond the fundamental frequency.