It began a process of standardisation of the voice: young tenors would model themselves on the most popular singers. The wide variety of different voices and styles which the earliest recordings reveal at the turn of the last century began to shrink as the public and critical sense of what a tenor was began to narrow considerably. By the 1950s the Italian style dominated the market - a tenor was expected to be rich, full-sounding and dramatic. Mario Lanza pre-eminently hypnotised a generation of singers; with Caruso he is the formative influence on the Three Tenors. Other traditions - such as the light and lyrical French and the Wagnerian Heldentenor - began to decline.

Potter is very good at the physicality of singing: the difference between the chest and head voice, for example, and the transition between the two and the placing of the larynx. As I learnt myself when I took singing lessons a few years ago, the process by which a voice is constructed is akin to working out in a gym as one's muscles, posture, breathing, internal spaces and vocal cords are strengthened and reconfigured.

There are also excellent chapters on national styles - French, Italian, German, English, Russian and American - and how they have grown out of very different vocal traditions and institutions. Our own has been shaped by the training of young voices in cathedral choirs and Oxbridge colleges, as well as by the lucky accident that one of the most important 20th-century opera composers, Benjamin Britten, was English.