Sol-Fa - The Key to Temperament Content from the guide to life, the universe and everything

Sol-Fa - The Key to Temperament

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This entry continues on from 'Sol-Fa - The Key to the Riddle of Staff Notation', and briefly discusses the subject of temperament in music, using Sol-Fa for reference.

Proportion

The six notes of the Guidonian hexachord (see the first entry in this series) fall naturally into the kinship of pure mathematical relations. The medieval and renaissance theorists didn't know about frequency, which is how we define pitch nowadays, but they knew the underlying maths. Indeed it had been known since Pythagoras, c500 BC, who worked out the mathematical relations for pipe lengths, string lengths, and bell weights. These all hold the same relationships as the inverse of the frequencies.

Frequency is measured in cycles (vibrations) per second, the units of measurement being named after scientist Heinrich Rudolf Hertz. A standard tuning fork defines the note A above middle C as 440 cycles per second, or 440Hz. Non-standard forks can also be bought.

If Ut has a frequency of 8 times x then Re is 9x, and Mi is 10x. The same relations bind Fa with Sol and La: if Fa is 8y, Sol is 9y and La is 10y. Furthermore, with Fa at 8y, Ut will be 6y; a relationship of 4 to 31. To put them all in a tidy line, we need to use bigger numbers. Taking x for granted from now on, we get these harmonious proportions:

La 40
Sol 36
Fa 32
Mi 30
Re 27
Ut 24

Now comparing those numbers we see that:

  • Ut-Re and Fa-Sol are both 8:9
  • Re-Mi and Sol-La are both 9:10
  • Ut-Mi and Fa-La are both 4:5
  • Ut-Fa, Re-Sol and Mi-La are all 3:4
  • Ut-Sol is 2:3
  • Ut-La is 3:5

Furthermore, the relation of any note to its octave above (e.g. C-c, D-d) is always 1:2.

Harmony everywhere! Well, almost: the only pairs whose relationships don't reduce to smaller numbers are Re-Fa and Re-La.

The names given to the intervals are:

1:2 perfect octave
2:3 perfect fifth
3:4 perfect fourth
4:5 major third
5:6 minor third
8:9 greater tone
9:10 lesser tone
15:16 diatonic semitone2

By tradition, the thirds, fourths, fifths and octaves are concordant3, and the tones and semitones are discords, when two notes are sounded together. The same consonances and dissonances apply to the inversion of each interval, that is, the intervals occurring when one of a pair of notes is flipped to its octave - making thirds become sixths and seconds become sevenths; sixths are concords, sevenths discords.

Prime numbers greater than five are not dealt with in classical European harmony at all, nor are their multiples - the Greeks counted the numbers up to four as concordant; five was added to the list in the 16th Century by the theorist Zarlino, having been the favourite consonance in practice for most of a century.

The Syntonic and Pythagorean Commas

Temperament issues arise from the fact that some notes require retuning if they are to join with others in perfect harmony. This happens not only between different hexachords, but even within the same hexachord: as we saw above, Re-Fa and Re-La are not harmonic intervals within a hexachord. Here are some notes for comparison between the original medieval 'hard', 'natural' and 'soft' hexachords:

Hard Hexachord Natural Hexachord Soft Hexachord Hard Hexachord
 d Lad Sol
 c Sol=c Fa
 b Fa/b Mi
 a La=a Mia Re
 G Sol=G Re=G Ut
 F Fa=F Ut 
E La=E Mi 
D Sol=D Re 
C Fa=C Ut 
B Mi 
A Re 
Γ Ut 

From here on in this entry the medieval distinction between capital and small letter-names is abandoned, and all members of any pitch class4 are taken as equivalent.

The notes B Fa and B Mi are a semitone apart, as shown in the first entry in this series. This is not a question of temperament. There are however other differences, small but problematic, between notes that are treated as equal.

Two As, Two Ds

'A La Mi' is not as high as A Re; and D La is not as high as D Sol.

If F Fa is 64 and G Re is 72 then A Mi is 80; but with G Ut still at 72, A Re is 81. Similarly, if C Sol is 72 then D La is 80; but with C Fa at 72, D Sol is 81.

This difference, the difference in size between the greater and lesser tone, was known to the ancient Greeks as the syntonic comma. It is about a fifth of a semitone5, which is clearly audible to untrained ears.

Flats versus Sharps: Never the Twain Shall Meet

Additional hexachords can be generated in both directions: denoting F as Sol will invoke a hexachord starting on Bb, introducing the note Eb, and so on towards the flat side; denoting G as Fa will produce one on D and introduce F#, and so on to the sharp side.

The sharps will never meet the flats; on the one side we reach Ab and on the other G#, but there is no reason why these two should be at the same pitch; and indeed they are not. The difference between Ab and G#, going round the cycle of fifths, is slightly larger than a syntonic comma6, and was called the Pythagorean comma by the ancient Greeks.

Practical Solutions

Some instruments such as concertinas have been traditionally made with separate buttons for Ab and G#. If one pitch is to serve for both then either:

  • One or more bad ('wolf') intervals must be tolerated between certain notes, or
  • Equal temperament or some other 'well-tempered' system must divide out the discrepancy among some or all of the intervals.

Some Temperaments

The tuning system most recommended in the medieval period was Pythagorean, which disregards the pleasantness or unpleasantness of the thirds altogether (after all, they were officially dissonances before Zarlino) and simply proceeds by pure fifths and fourths (2:3 and 3:4). Tuning all twelve notes of a keyboard we will end up with the 'wolf' interval between our first note and the last: too big by a Pythagorean comma, if that interval is a fourth, too small if it is a fifth. Most of the major thirds (Ut-Mi) that come out as a result are unpleasantly wide (by a syntonic comma, since we generate only greater tones, and no lesser tones). However, a strange coincidence happens towards the end of our tuning: a third that straddles the wolf fourth will become wonderfully pure, as the two wrongs in this case make a right, and the Pythagorean comma almost exactly cancels the syntonic comma. Since we can choose which will be our first and last notes to tune, we can place the wolf fourth wherever we like. Putting it between D and A (this means tuning A as Bbb) would result in beautifully-tuned chords of F major, C major and G major. D major would have a lovely third but a very nasty fifth.

A partial solution, widely used in the Renaissance, is mean-tone tuning, which yields a fair number of good chords. It is done by dividing Ut-Mi (4:5) into exactly equal steps - Ut:Re:Mi becomes 4:√20:5 - and it sounds very pleasant in keys with few sharps or flats. Its incompleteness, however, led to many different versions being tried: quarter-comma mean-tone, fifth-comma, sixth-comma and so on.

Tuning a guitar to four perfect fourths and a pure major third will leave the top E flatter than the bass E by exactly a syntonic comma. Widening all the intervals equally will approximate to fifth-comma mean-tone tuning. This is complicated by the placing of the frets, which are normally equal-tempered, though many guitar-makers (particularly in Spain) flatten7 the second fret; experience shows that an equal-tempered second fret always sounds too sharp. String physics, rather than mathematical considerations, may account for this. A solution that many guitarists use is to tune all the bottom strings fairly pure and tune the top two more widely; this will sweeten the chord of A, the guitar's home key, and also D and G; but the E chord will have a bit of a rasp with its flat fifth.

Temperament makes a great difference to an organ, since a triumphant long-drawn-out final organ chord is heard without any decay of the sound, and without any chance of adjustment. For this reason, organ tuners in England held on to mean-tone tuning, and only gave in to equal temperament around 1850.

Some viol players split their first fret, to give a sharp Bb on an A string but a flat C# on a C string. Others adjust the tuning as they go, as a large alteration can be made by pushing or pulling a string with the fretting finger.

Equal temperament was proposed by Aristoxenus around 350 BC, rejected for almost two thousand years, then championed by Rameau in the 18th Century and only more-or-less-universally applied since around 1850; by which time the early-music movement had begun, which has reinstated unequal temperaments for performing period music. Equal temperament is arrived at by dividing the octave into twelve equal semitones, using the 12th root of two8.

In equal temperament every interval except the octave is compromised - the harmonious mathematical relationships are hinted at rather than sounded. The biggest difference equal temperament makes to the sound of a chord is that the major thirds are too wide, by about one seventh of a semitone. Musicians other than keyboard players can and do bend the tuning of these notes to add a glow to significant chords. Of course they also bend notes for expressive reasons, as well as harmonious ones.

Plucked instruments work well in equal temperament, perhaps because their sound dies out and seems to adjust itself miraculously in the process. Pianos are in the worst position; because of the high tension on their frames, they suffer from a condition called 'inharmonicity', which is offset by tuning their octaves wide. String players accordingly need to adjust their intonation when playing with piano accompaniment.

Many varieties of mean-tone temperament were used in the Renaissance, and the 17th and 18th Centuries saw even more inventive systems come into vogue. Theorists searched for a system that would give as many good chords as possible in as many keys as possible. JS Bach wrote two sets of preludes and fugues in all twelve major and twelve minor keys, known as the Well Tempered Clavier9; it appears that when he wrote the first book of his '48', Bach did not use equal temperament but a well-tempered system close to those of Werckmeister and Neidhardt. However by the time he wrote the second book (the second set of twenty-four preludes and fugues) he had come round to equal or near-equal temperament. These systems sought to keep a pleasing variety between keys; others purposely made distant keys more discordant than familiar keys, so that a composer could increase the drama of his compositions by straying into those outlandish keys before returning to a comfortable conclusion.

Vallotti's 1754 system, now favoured by many viol players, makes several of the commonly used thirds harmonious by dividing the Pythagorean comma between all the 'natural' notes (six fifths: F-C-G-D-A-E-B), while the six fifths incorporating 'black' notes10 (B-F#-C#-G#-Eb-Bb-F) remain pure.

Further Information

A practical demonstration of 34 historical temperaments, with a program to create and hear temperaments of your own, is to be found at the WinTemper site.

1It is vital to distinguish proportion from arithmetical sequence. These relations between notes are all proportional, so the step from 8 to 9 is not the same size as the step from 9 to 10. Rather than 'an increase of one' it is 'an increase of one-eighth'. Therefore 24-to-27 is the same 'interval' as 32-to-36. It can be written as 8:9, or as a fraction.2The chromatic semitone, Bb-B, is smaller than the diatonic semitone. The proportion is 128:135, which is close to 18:19.3The fourth is an exception: a fourth is treated as discordant, unless there is another concordant note below it in a chord. This has to do with the language of harmony, rather than the science of acoustics.4A pitch class is defined as all the octaves of a note: all the As make up the pitch class A.5A fifth of a semitone registers as twenty cents on an electronic tuner. You can generally get away with tuning five cents above or below your desired pitch, before discrepancies become painful when two instruments play the same note.6The proportion is 219:312, or 524288:531441, which is between 73:74 and 74:75 (for the purpose of comparison with the syntonic comma, 80:81), and almost a quarter of a semitone.7'Flatten' in this context means 'place closer to the nut'.8Aristoxenus seems to have done it by ear: he was a practical musician. A rough calculation of the 12th root of two to four decimal places was made, but not published, in the 1580s by a Dutch mathematician, Simon Stevin; the advent of logarithms in 1617 made it an easier matter. The implementation of equal tempered tuning on keyboard instruments was recommended by the respected composer Frescobaldi (1583-1643) but a teachable tuning method was not worked out for another hundred years.9Also known as Bach's '48'. Clavier simply means keyboard.10Black keys on the piano keyboard.

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