Quite a number of my recent articles for Gramophone have touched on issues of tuning, not because I’m trying to promote a particular point-of-view – you know me, I’m not one for stirring up controversy – but because the material I’ve been dealing with has forced my hand. Tuning is a hot topic, not a subject that ought to be dodged.

In the latest issue of the magazine I interview the Hilliard Ensemble, the four-man vocal group who have spent the last 40 years immersing themselves in arcane tuning systems. Or as the group’s tuning guru, the tenor Rogers Covey-Crump, implies in the article, tuning systems that offer a more nuanced expressive palette than plain ordinary equal temperament, the default system by which modern orchestras and instruments are tuned.

The Austrian composer Georg Friedrich Haas, who I profiled in Gramophone’s November issue, is tuning mad. His ensemble piece in vain, performed this coming weekend at the Southbank as part of The Rest Is Noise festival, plays out a dramatic polemical clash between ‘new’ equal temperament and ‘old’ tunings of the type the Hilliard Ensemble would be happy to call their own. And in that same issue, in my review of Evelinde Trenkner and Sontraud Speidel performing Bruno Walter’s four-hand piano transcriptions of Mahler symphonies, I note that the piano’s equal temperament refuses to bend towards 'the more gamey intonation we’ve become accustomed to in Mahler.'

But why is tuning a problem and why are some musicians concerned about equal temperament? Quasi-scientific terminology and frankly terrifying looking mathematical ratios are never too far away for any discussion about tuning. The crux of the argument, though, is as follows. Tuning starts from fundamentals. The note C is not a self-contained phenomenon. Each note encompasses within it an underpinning spectrum of overtones – essentially a sonic vertebrae – of all other notes. This principle is comparable to the colour spectrum, where the colour red doesn’t suddenly turn yellow; the redness of any red contains within it the yellow it is about to become. And tuning wars are fought over how best to rationalise that underlying spectrum.

War? That’s an emotive word isn’t it? Well, actually no. When I interviewed the American composer Lou Harrison in 2002 his benevolent demeanour – John Cage meets Santa Claus – shattered as I broached the subject of tuning. 'Equal temperament destroys everything and is not for the human ear,' he snarled as though the fault were mine. Terry Riley thinks equal temperament is emblematic of what he considers to be the West’s driven aggression and imperialist tendencies: 'Western music is fast because it’s not in tune,' he says.

And steel yourself gentle reader, because the argument’s about to hot up. Equal temperament is a pragmatic system of tuning that allows composers access-all-areas up and down that spectrum of notes. It’s a system that overcomes the acoustic problem of shifting tonal centre from, say, C to somewhere remote, like B, where suddenly that spectrum of overtones will fall out of mathematical alignment and the music gets yanked audibly out of tune. It remedies the problem by twisting notes into a compromised congruence; for example the 11th harmonic up from C, a slightly sharpened F, is flattened and made consistent across keys and scales. The problem being that, as far as Lou Harrison was concerned, nuanced shadings of tuning have been sacrificed for the sake of convenience: like one synthetic red has replaced an infinite variety of reds which could, anyway, be about to turn yellow.

While we’re on the subject of flattening, let’s sit on a particularly pernicious and enduring myth. Bach’s Well-Tempered Clavier has precisely nothing to do with equal temperament as we now understand the term! Fair enough, Bach’s masterwork was an attempt to write a cycle of keyboard works in all keys, the clincher being whether his central E flat minor Prelude would fall into tuning alignment with the D sharp minor Fugue. But no, ‘well-tempered’ and ‘equal temperament’ are not interchange terms. Bach was experimenting with a temperament that might have been more equal than what had gone before: but that’s not the same as modern-age Equal Temperament.

So what had gone before? How was music tuned before ideas about the desirability of equalising temperament began to circulate? In my interview with the Hilliards, Rogers Covey-Crump describes the difficulties the group had in maintaining music by Orlande de Lassus at a stable pitch until – bingo! – the eureka realisation that in Lassus’s world quarter-comma meantone temperament was commonplace. Which meant sharpened fourths. And with the fourths duly sharpened, the tuning problems went away.

Baroque tuning systems tend to have labels like that. Bach’s system of choice was Werckmeister III; other widely used systems included Temperament ordinaire, Kirnbeger temperament, septimal meantone. But all these systems boiled down to scratching the same itch – ideas often governed by need, taste or circumstance of how best to carve up the basic octave as conceptualised by Pythagoras. The Hilliards work in Just Intonation, also Lou Harrison’s preferred system. And Just Intonation emphasises bright, booming perfect thirds, but the way the maths works out, that means the fifth between D and A is pushed out of tune. Equal temperament pretends you can have it both ways; Just Intonation makes a conscious choice about which intervals matter most. In meantone tuning, the thirds are kept as perfect as they can be, and the maths tries to ‘lose’ the discrepancy within the fifths by spreading the awkward ratio over more octaves.

Lou Harrison, and fellow travellers like La Monte Young, Tony Conrad and Terry Riley, have variously equated the impact of equal temperament on sound with nuclear war, the cloned homogenisation of globalisation and destruction of the natural environment. The argument goes that equal temperament is becoming increasingly streamlined and corporate, and man’s capacity to hear and feel subtle inflections of tuning is in slow retreat. We need to be aware not only if notes are in tune, but also whether the system in which those notes have been tuned is appropriate – whether music is in tune with us.