Ladefoged & Johnson – A course in phonetics – Chapter 8 – Acoustic phonetics

Links the source-filter model to spectrograms and acoustic analysis of speech.

Handbook of phonetic sciences – Ch 20 – Intro to Signal Processing for Speech

Written for a non-technical audience, this gently introduces some key concepts in speech signal processing.

Ladefoged (Elements) – Chapter 5 – Resonance

Now we turn to speech production, and resonance is how the vocal tract shapes the quality of sound, to produce different vowels, for example.

Ladefoged (Elements) – Chapter 2 – Loudness and pitch

These are perceptual phenomena that relate to physical properties of sound.

Ladefoged (Elements) – Chapter 1 – Sound waves

Very brief, but a reasonable place to start if you have no idea what sound is.