Source: https://jmrplens.github.io/phonometry/guides/sections/psychoacoustics/ Psychoacoustics replaces the question "how many decibels?" with "what does the listener perceive?". Its base quantity is **loudness**: a perceptual magnitude in sones, computed by auditory models that account for the ear's filtering, masking and compression. On top of loudness sit the **sound quality** sensations that distinguish two equally loud sounds: sharpness (high-frequency emphasis), tonality (audible discrete tones), roughness (fast modulation) and fluctuation strength (slow modulation). And on top of those sits a combined **annoyance** metric that weighs them into a single scalar. [Loudness](/phonometry/guides/loudness/) is the foundation page. It covers the three model families phonometry ships (Zwicker per ISO 532-1, Moore-Glasberg per ISO 532-2/3, and the Sottek Hearing Model of ECMA-418-2) together with the ISO 226:2023 equal-loudness contours that anchor the perceptual scale for pure tones. [Sound Quality Metrics](/phonometry/guides/sound-quality/) adds sharpness per DIN 45692 and the ECMA-418-2 tonality, roughness and fluctuation strength that share the Sottek front-end. Tones in noise get two dedicated pages because two different questions are asked of them. [Prominent Discrete Tones (ECMA-418-1)](/phonometry/guides/tone-prominence/) answers a product-noise question: is this tone *prominent* by the tone-to-noise and prominence-ratio criteria used in IT-equipment declarations? [Objective audibility of tones in noise (ISO/PAS 20065)](/phonometry/guides/tone-audibility/) answers an environmental one: by how many decibels does the tone exceed its masking threshold, the audibility that feeds the tonal penalty of ISO 1996-2. [Psychoacoustic annoyance and fluctuation strength](/phonometry/guides/psychoacoustic-annoyance/) closes the chain with the Fastl & Zwicker model, which combines loudness, sharpness, roughness and the slow-modulation sensation of fluctuation strength into a single annoyance value. Read it last: it consumes everything the other pages define. ## Pages in this section - [Loudness](/phonometry/guides/loudness/): Zwicker, Moore-Glasberg and Sottek loudness in sones, plus the ISO 226:2023 equal-loudness contours. - [Sound Quality Metrics](/phonometry/guides/sound-quality/): sharpness (DIN 45692) and ECMA-418-2 tonality, roughness and fluctuation strength. - [Prominent Discrete Tones (ECMA-418-1)](/phonometry/guides/tone-prominence/): tone-to-noise and prominence ratios with prominence verdicts. - [Objective audibility of tones in noise (ISO/PAS 20065)](/phonometry/guides/tone-audibility/): the audibility of a tone above the masking threshold, feeding the ISO 1996-2 tonal adjustment. - [Psychoacoustic annoyance and fluctuation strength](/phonometry/guides/psychoacoustic-annoyance/): the Fastl & Zwicker annoyance model and the fluctuation-strength models it consumes.