Source: https://jmrplens.github.io/phonometry/guides/sections/hearing-perception/ A sound pressure level says how much sound there is; this section is about what a **listener** makes of it. Its three subsections answer three different questions. **Psychoacoustics** quantifies sensations: how loud a sound is perceived to be, how sharp, rough or tonal it is, and how those sensations combine into annoyance. **Speech** asks how well spoken words survive the trip from a talker to a listener, through a room, a sound system or background noise. And **hearing and exposure** covers the ear itself: where the hearing threshold sits across age and population, how noise permanently shifts it, and how a working day's exposure is measured and reported. The three build on each other in one direction: the psychoacoustic models consume calibrated signals or band spectra from the [core analysis](/phonometry/guides/sections/core-signal-analysis/); the speech indices consume band levels and, in the SII's case, the hearing thresholds that the exposure pages quantify; and the exposure metrics feed the hearing-damage model of ISO 1999. A good entry point is [Loudness](/phonometry/guides/loudness/): it introduces the perceptual scale (the sone) and the auditory models that most other metrics in this section reuse or extend. ## [Psychoacoustics](/phonometry/guides/sections/psychoacoustics/) The perceptual sensations of sound: loudness and the metrics layered on it. - [Loudness](/phonometry/guides/loudness/): Zwicker (ISO 532-1), Moore-Glasberg (ISO 532-2/3) and Sottek (ECMA-418-2) loudness in sones, plus the ISO 226:2023 equal-loudness contours. - [Sound Quality Metrics](/phonometry/guides/sound-quality/): sharpness (DIN 45692) and the ECMA-418-2 Sottek Hearing Model tonality, roughness and fluctuation strength. - [Prominent Discrete Tones (ECMA-418-1)](/phonometry/guides/tone-prominence/): the tone-to-noise and prominence ratios that decide whether a discrete tone is prominent. - [Objective audibility of tones in noise (ISO/PAS 20065)](/phonometry/guides/tone-audibility/): the engineering method for 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 combining loudness, sharpness, roughness and fluctuation strength. ## [Speech](/phonometry/guides/sections/speech/) Two complementary indices of speech intelligibility: STI rates the transmission channel, SII rates the listening condition. - [Speech Transmission Index (STI)](/phonometry/guides/speech-transmission/): the IEC 60268-16 modulation transfer function, the indirect method from an impulse response, and direct STIPA measurement. - [Speech Intelligibility Index](/phonometry/guides/speech-intelligibility/): the ANSI S3.5-1997 one-third-octave-band SII from speech, noise and hearing threshold spectra. ## [Hearing and exposure](/phonometry/guides/sections/hearing-exposure/) The hearing threshold, what noise does to it, and how exposure is measured. - [Hearing threshold (age and reference zero)](/phonometry/guides/hearing-threshold/): the ISO 7029:2017 age-related threshold distribution and the ISO 389-7:2005 reference threshold of hearing. - [Noise-induced hearing loss (ISO 1999)](/phonometry/guides/noise-induced-hearing-loss/): the noise-induced permanent threshold shift and its combination with age into HTLAN. - [Occupational Noise Exposure (ISO 9612)](/phonometry/guides/occupational-exposure/): the task-based, job-based and full-day strategies for LEX,8h with the Annex C uncertainty budget.