Caravaggio (Michelangelo Merisi), “I musici”, 1597. The Metropolitan Museum of Art, Open Access (public domain).
People say period instruments and it sounds like a collectors’ matter. It is not. Between a modern orchestra and one that plays with eighteenth-century instruments and techniques, the differences are physical, measurable, and audible in the first three seconds. It is worth knowing what they are, because without knowing you judge the result by how it seems, which is a leaner sound, and not by what it is.
The first difference is the strings. Until well into the nineteenth century the strings of bowed instruments were made of gut, that is, dried and twisted animal intestine, not metal. Gut works at a lower tension and with a larger diameter, and the sound that comes out has less projection, more friction and a softer attack. In practice: the note begins an instant later and ends sooner. The consequence is that phrases breathe differently and short articulations become natural instead of laborious.
The second is the bow. The Baroque bow is convex and lighter, and it is not made to hold a long note equal to itself. Every stroke has an inside and an outside, it swells and fades on its own. The modern bow, the one François Tourte perfected in Paris towards the end of the eighteenth century, is concave, heavier and designed for exactly the opposite, that is, for the long sustained sound that Romantic music and ever larger halls required. Changing bow means changing grammar.
The third is vibrato. In the eighteenth century it was an ornament, used on certain notes to give colour, like a spice. Continuous vibrato on everything, the sound we now consider the normal sound of the violin, establishes itself between the late nineteenth and early twentieth century, and recordings from the first decades of the century document it in the middle of changing. Playing Vivaldi with constant vibrato is not wrong because of a rule, it is wrong for a practical reason: it covers the dissonances, and in that music the dissonances are the event.
The fourth is the overall pitch. The reference A in the early repertoire is conventionally taken lower than the modern one, which means less taut strings, hence still less tension and more free resonance of the harmonics. The difference is heard above all in the voices: parts written for eighteenth-century sopranos, sung a semitone lower, stop being acrobatics and go back to being singing.
The fifth concerns the wind instruments, and it is the most drastic. Early trumpets and horns have no valves: you play the series of natural harmonics, and the notes outside the series are corrected with the hand or simply are not there. This means certain notes are bright and others opaque, and composers wrote with that inequality in mind. On a modern instrument all the notes are equal, and an effect that was intended disappears without anyone noticing.
The sixth is the number of people. A Bach orchestra in Leipzig numbered between eighteen and twenty-five players, often one to a part. The same music played by sixty people is not the same music louder, it is another texture, because the inner lines stop being individuals and become a blend.
The honest point is that none of these choices is automatically better. A modern orchestra playing Vivaldi with an awareness of these six differences can do something magnificent, and a period ensemble can be as dull as a doctor’s waiting room. What changes is that, knowing them, you stop listening in order to judge and start listening in order to recognise.
An experiment for tonight, ten minutes. Take the first movement of a concerto from L’Estro Armonico, listen to twenty seconds in a recording from the 1950s and twenty seconds in one from the last twenty years on period instruments, and do not look at which is more beautiful. Count only two things: how long the held notes last, and how much you can hear the bass. They are the two indicators that tell all the rest.