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

8.1. THE IMPEDANCE MODEL 115
The string fingering may be set either "OPEN" or "CLOSED". The member boreRadius in
both the EmbouchureHole structure and the Hole structure is the radius of the bore at the position
of the hole. The Hole structure may contain a Key member, which contains the relevant
parameters describing the extent of shading of a hole by an open key:
typedef struct key_str {
double radius;
double holeRadius;
double height;
double thickness;
double wallThickness;
double chimneyHeight;
} *Key;
(For a tone hole without a key, Key = NULL.)
Functions implemented in Woodwind.c calculate transfer matrices of the various structures
and the input impedance of the entire instrument. The Woodwind structure is used by the
processes ‘Impedance’, ‘PlayedImpedance’ and ‘Waves’.
8.1.3 ‘Impedance’
The process ‘Impedance’ calculates the input impedance of a woodwind defined by an XML
file and is implemented in the C program Impedance.c (Listing B.10). The program has the
following usage:
Usage: Impedance [OPTIONS]
Options:
-s
-t (default 25.0 degC)
-u (default 0.5)
-l (default 100.0)
-h (default 4000.0)
-r (default 2.0)
-e (default 1.0)
:
- Optional if no holes are defined in XML file.
- Must be a sequence of 'O' (open hole) and 'X' (closed hole)
characters.
- Length must be equal to the number of defined holes.
- e.g. "XXOOOOOOXOOOOXOOO"
The mandatory argument XML file is the path to the file describing the instrument. This
file is validated against the DTD file Woodwind.dtd which must be in the same directory as the
XML file. Options are provided for setting the temperature (in °C), the relative humidity and the
frequency range (Hz). The parameter entryratio allows calculation of the input impedance
as seen through a radius smaller than the entry radius of the instrument. Thus entryratio