Flute acoustics: measurement, modelling and design - School of ...

116 CHAPTER 8. SOFTWARE IMPLEMENTATION
must be less than or equal to one. The parameter holestring sets the fingering for the instrument
and consists of a sequence of 'O' or 'X' characters (for open and closed holes respectively).
For example, the following command would output an impedance spectrum for a
modern flute:
Impedance -s XXXXOOXXOOXXXXOX -t 23.0 -h 0.8 ModernFlute.xml
‘Impedance’ parses the XML file into a Woodwind structure, calculates the speed of sound
and density of air given the passed-in (or default) values of temperature and humidity, and
calls the function impedance(double f, Woodwind w) in Woodwind.c for each frequency
of interest. ‘Impedance’ then prints three columns of data: the frequency, and the real and
imaginary parts of the impedance. Typical output looks like
2.000000e+002 1.103451e+005 2.442222e+006
2.020000e+002 1.149588e+005 2.495417e+006
2.040000e+002 1.198377e+005 2.550284e+006
...
8.1.4 ‘PlayedImpedance’
The process ‘PlayedImpedance’ is similar to ‘Impedance’ but differs in several important ways.
Firstly, the process calculates the input impedance of a played instrument; that is an instrument
containing air of a composition more like exhaled breath than ambient air, and with a
temperature gradient along its length (the properties of air in a played flute are discussed in
§2.2.1). The temperature and humidity along the instrument are calculated by the model, and
cannot be passed in as parameters. Secondly, the returned impedance is the sum of the instrument
input impedance and the player (face) impedance (i.e. the radiation impedance as
baffled by the player’s face, especially lips); and the latter changes over the range of the instrument.
Thirdly, the program is designed to calculate many impedance spectra at once, and
the fingerings for the instrument are input as a file rather than as a string. Since the output of
‘PlayedImpedance’ depends on the note played (through the face impedance), and not just on
the fingering, the input file is a list of tab-delimited MIDI numbers and fingerings, such as the
following for a Boehm flute with C-foot:
60 XXXXXXXXXXXXXXXX
61 XXXXXXXXXXXXXXXO
62 XXXXXXXXXXXXXXOO
...
The usage for ‘PlayedImpedance’ is as follows:
Usage: PlayedImpedance [OPTIONS]
Options:
-l (default 200.0)
-h (default 4000.0)
-r (default 2.0)
: