This book was a gift from
a former student and, to my shame, I hadn’t got round to reading it until this
summer. It took a while (even after I
had started!).
It’s a fairly academic
book about the maths behind music.
I was expecting to read
about patterns made by sand on drumskins, tuning-systems, Pythagorean commas,
etc, and while these did feature, there was so much more too.
The Musical Offering
To start with, having some
musical knowledge was useful. The title,
for example, is a play on the title of an extraordinary work by JS Bach (The
Musical Offering). Frederick the
Great, King of Prussia asked Bach to improvise on a melody which the King
provided (and perhaps composed). Bach later
wrote a collection of variations on the theme, including pieces where you can
play the music forwards and backwards simultaneously, or with one part at half
the speed of another, or in mirror image, and culminating in a 6-part fugue.
Pythagorean comma
The Pythagoreans knew
about music and vibrating strings. They
knew that an interval of an octave corresponds to a ratio of 2:1 (nowadays we
would say the frequency of the note is doubled) and a perfect fifth is 3:2 (these
values can be used to create ‘harmonics’ on a guitar or violin). On a piano, if you go up in fifths, it takes
12 of them before you arrive back at the same note (seven octaves higher than where
you started). For example:
C – G – D – A – E – B – F#
– C# – G# – Eb – Bb – F – C
This should mean that 1.5
(from the ratio 3:2) to the power of 12 is equal to 2 (from the ration 2:1) to
the power of 7 (because that final C is 7 octaves higher than the initial
one). Unfortunately it doesn’t:
1.5^12 = 129.746…, while
2^7 = 128
The discrepancy is known
as a ‘Pythagorean Comma’.
This comes about because of
the sleight-of hand where G# moved up a fifth to make Eb. On a keyboard we have to treat G# and Ab as
being the same note – whereas in this perfect Pythagorean world they are
different notes. If we continue to go up
in fifths, remaining with sharps (rather than switching to flats) we get:
C – G – D – A – E – B – F# – C# – G# – D# – A# – E# – B#
Again, keyboard players
would see B# as being identical to C natural, but in fact (as the Pythagorean
comma tells us) it is a little higher than the C.
It doesn’t matter if we
decide to go down in fifths: the D-double-flat we end up on is lower than the C
natural it is deemed to be equivalent to.
And it doesn’t
matter if we go up in perfect fourths (ratio 4:3). 12 of them gives 31.569, which is less than
the 5 octaves value of 32.
Even a major
third is unhelpful. The ratio is 81:64,
and three stacked major thirds ‘should’ make an octave (C – E, E – G#, Ab – C –
but there’s the sleight of hand with G#=Ab again). (81/64)^3 = 2.027…, which is a shade above 2.)
Back to the book!
Lots of cool stuff like
this, which I could understand and which taught me lots of new things.
Some almost
incomprehensible (to me) stuff. I did
struggle through the chapter on Fourier Theory, but was relieved the author said
this could be skipped! Here’s a sample:
And some lovely stuff
about transformations, wall-paper patterns, etc. See some neat symmetry here:
In summary, if I didn’t
have any prior knowledge at all I probably wouldn’t have finished it. And clearly it is aimed at those in the
intersection between maths and music (without one or the other you probably won’t
get much out of this). I did glaze over
at the extent of the calculus that was involved. But I learned some cool new things too.
Worthwhile.