The tempering of the intervals in the middle octave is called “laying the bearings” and is the most difficult, as it is the most important, of the various processes incident to the practice of pianoforte tuning. The “accumulation of insensible into almost intolerable errors,” as Mr. Ellis aptly terms it, continually besets the path of the tuner, especially if his preliminary knowledge be imperfect. The true estimation of beats, as generated by various intervals, is an art that is but slowly and painfully acquired, by long practice and training of the ear.
Examination of the pianoforte key-board shows us thirteen sounds within the compass of an octave. In proceeding to the conversion of these into equally tempered sounds, we have more than one method presented to us. We shall, of course, choose the octave which, as stated above, runs from F below middle C to F above it, and shall use, for our purposes, such adjacent sounds as we may consider necessary.
It is usual to take from a tuning-fork the pitch of the sound from which the tuning is begun. These instruments are tuned either to C, or A next above middle C. It is usual, in this country, to tune from C, and we shall, therefore, adopt that method.
Now there are various ways of setting about the “laying of the bearings.” Some tuners work by thirds, others by fourths and fifths; others again use a series or circle of fifths joined by octaves. Whatever intervals are tuned, the idea is to include all the thirteen sounds within the octave and to use, as far as possible, only one or two kinds of intervals.
Of all these methods, the shortest, easiest and most accurate is that which employs fourths and fifths only. It is used in such a manner that, by tuning a circle of fifths and fourths, the last sound tuned provides the octave to the first, thus completing the circle and the octave of tempered sounds.
1. Pitch C is tuned by the tuning fork. 2. F below pitch C is tuned, being a tempered fifth. 3. G below pitch C is tuned, being a tempered fourth. 4. D above G is tuned, being a tempered fifth. 5. A below D is tuned, being a tempered fourth. 6. E above A is tuned, being a tempered fifth. 7. B below E is tuned, being a tempered fourth. 8. F sharp below B is tuned, being a tempered fourth. 9. C sharp above F sharp is tuned, being a tempered fifth. 10. G sharp below C sharp is tuned, being a tempered fourth. 11. D sharp above G sharp is tuned, being a tempered fifth. 12. A sharp below D sharp is tuned, being a tempered fourth. 13. F above A sharp is tuned, being a tempered fourth.