Speech Science & Phonetics (Acoustics, IPA, Distinctive Features)

Overview

Speech science explains how a sound is made, what it looks like acoustically and how listeners hear it. Exam items test the physics of sound, the source-filter model, vowel and consonant acoustics, IPA transcription, distinctive features and the acoustic voice measures clinicians use. Laryngeal Anatomy & Voice Production covers vocal fold vibration and typical F0 values; Voice Assessment covers acoustic measures in the clinic; Phonological Development covers how children acquire sounds; Hearing & Audiogram Interpretation covers dB HL on the audiogram.

Sound Basics

• Periodic sounds repeat (voicing, a sine tone); aperiodic sounds do not (the noise of /s/, a whisper).
• A complex periodic sound has a fundamental frequency (F0) and harmonics at whole-number multiples of it: with F0 at 100 Hz, harmonics fall at 200, 300, 400 Hz and so on.
• The decibel is a logarithmic ratio, so dB values do not add like ordinary numbers. A 10 dB rise sounds roughly twice as loud; a 6 dB rise doubles sound pressure.
• dB SPL is referenced to a fixed physical pressure. dB HL is referenced to average normal hearing at each frequency, which is why the audiogram's 0 dB HL line is flat although human sensitivity varies with frequency.
• Young adults with healthy ears hear roughly 20 to 20,000 Hz. Most vowel formant and many consonant cues lie between about 500 and 3,000 Hz, while fricatives such as /s/ carry energy higher, which is why high-frequency hearing loss erases them first.