People generate sounds by breathing air through the vocal chords, which resonate, and then controlling the production of sound by varying the shape of their vocal tract, mouth, tongue and so on. For the purposes of communication, speech is generally more useful than music, and happens to use a constrained part of the frequency and power range that humans are capable of generating - and a much more constrained part of the range than they are capable of hearing. Typically, we can generate sounds over a dynamic range of 40 decibels, For recognisable speech, the vast majority of important sounds are in the frequency range 60H to 8000Hz (compared with music which is typically audible up to nearly 20KHz).
Speech is made up of sound units called phonemes (the smallest unit of distinguishable sound). These are specific to a language, so for example ,we find that English and Japanese each have phonemes that the other language does not (e.g. ``l'' and ``r'') (hence the difficulty in learning to pronounce another distant language). We illustrate some of the international phonetic alphabet for British English with example words in the table 4.1 below.
Phonemes are vowels or consonants, where vowels are either pure or diphthongs (made of two sounds), and consonants may be semi-vowel, fricative (use teeth to make), plosive (use lips ) or nasal (use nose). Other factors influencing the sound we make are stress (change of strength), rhythm and pace, and intonation (pitch).