Tuning and Temperament
All stringed early keyboard instruments constructed on historic principles require fairly frequent tuning. The wood of the case breathes with changes in temperature and, more importantly, humidity. The strings react to changes in temperature, and this is particularly noticeable where more than one metal is used for stringing, as often happens. Harpsichords and spinets will need retuning after major changes in the weather, and tuning at regular intervals of two weeks to two months when the weather is basically stable. Smaller instruments, particularly if strung in one metal as is the case with many clavichords, require less frequent regular tuning. Because of this, most early keyboard owners learn how to tune their instrument.
There is a basic problem in tuning a musical scale, which arises because some combinations of pure intervals are mathematically incompatible with others. This can be very obvious to the ear. There is no way that a keyboard can be tuned so that all the intervals which can be played on it are pure. The many tuning systems which have been invented to overcome this problem are known as temperaments.
One possibility is to divide each octave into twelve equal intervals. This is a neat mathematical solution, but it results in flattened fifths and badly out of tune thirds and sixths. This does not matter too much with the modern piano, where it is the standard tuning system, but with the harpsichord these dissonances can easily be heard. It is also difficult to tune well by ear. For these reasons equal temperament was never used for tuning the harpsichord during its historic period, though the system had been known for centuries.
Many compromise temperaments have been developed over the centuries by music theorists and musicians. They differ from one another by the way in which they distribute the basic error which is the cause of the problem. They enable music played in frequently used keys to be much more nearly in tune than with equal temperament, at the expense of rarely used keys. The subtly different sounds of the individual keys are known as key flavour. While the temperaments are well documented, there is still some uncertainty about their use in the historic period. We do know that some form of mean-tone tuning was used in England from the latter part of the 16th century until just over 100 years ago. In this, intonation is very good in six major and three minor keys, and unlike equal temperament, many thirds and sixths are well in tune. However, four major and four minor keys are unusable. Elsewhere, so-called good temperaments such as those of Werckmeister, Kirnberger and Valotti, were preferred. In these, music can be played in all keys, some of which are more in tune than in equal temperament and some less. An instrument so treated is called well-tuned, and it is noticeably refreshing to escape from the uniformly boring equal tuning in which all keys are the same amount in error.
There are three aspects to tuning: the physical technique with the tuning key; learning how to hear when a note is in tune; and understanding what has to be achieved. Tuning key technique is quite easy to acquire; the string tensions in a harpsichord are very much lighter than those in a piano. Paradoxically, you don't need to have a very musical ear to tune well, and here again the lighter stringing helps, because individual notes sound purer than on a piano. When two notes are sounded together, if they are in tune they will reinforce each other; but if they are slightly out of tune, they will beat together or wow. The effect is quite obvious once it has been pointed out. You tune by listening to the wow, and either eliminating it or controlling it to a fixed number of beats per second, by reference to a tuning table. The historic temperaments usually have several pure fifths, and maybe some pure thirds as well, and are much easier for an amateur to tune than equal temperament. The more regularly you tune a harpsichord, the better you keep in practice. Once you have mastered the art you will find it needs about 45 minutes for a three-register harpsichord, and about 15 minutes for a spinet.
Apart from tuning tables, which can be found in books on the subject, there are a number of useful aids to accurate and rapid tuning. Today these are all electronic, either as stand-alone devices or as Apps for Smart Phones: an excellent example being 'Cleartune'.