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

8.1. THE IMPEDANCE MODEL 117
- Must be a tab-delimited list of midi numbers and
holestrings, one set per line.
The output of ‘PlayedImpedance’ is a table of impedance magnitudes. The first column contains
the frequency and the first row the MIDI numbers (aligned with the corresponding impedance
vector). The impedance values are given in a logarithmic scale and are equal to 20log 10 Z 0
|Z |
where Z 0 = 1Pasm −3 . The output for the input file snippet given above would look like
60 61 62
200.00 124.178 126.977 129.918
202.00 123.710 126.512 129.414
204.00 123.241 126.053 128.925
206.00 122.770 125.599 128.448
208.00 122.296 125.148 127.981
210.00 121.818 124.701 127.524
...
If the output from ‘PlayedImpedance’ is directed to a file, the file can then be used as
the input to the process ‘AnalyseNotes’, which derives musically useful information for each
note from its impedance spectrum. ‘PlayedImpedance’ is implemented in the C program file
PlayedImpedance.c (Listing B.22) and most of the important functions are implemented in
the files Woodwind.h and Woodwind.c.
8.1.5 ‘AnalyseNotes’
The process ‘AnalyseNotes’ is implemented in the C file AnalyseNotes.c (Listing B.3). ‘AnalyseNotes’
calls functions in Minima.h and Minima.c (Listings B.13 and B.14) to retrieve the
frequency, impedance and bandwidth of impedance spectrum minima and calls functions in
Analysis.h and Analysis.c (Listings B.4 and B.5) to determine (among other things) the
playability and strength of the impedance minima. These programs are largely the work of
Botros (2001), and detailed documentation is available in his thesis. The interfaces for the programs
have been modified slightly for this thesis and minor changes have been made to some
files.
‘AnalyseNotes’ searches for minima in each impedance spectrum in the passed-in file, and
determines the frequency, impedance and tuning of each minimum. These quantities are approximated
from a parabola fitted to eleven data points centred on the minimum and spanning
a frequency range of 20 Hz. If the impedance curve corresponding to some played note
has a playable minimum nearest to that note, then the minimum is analysed and the playability,
strength and harmonicity are output along with the frequency and tuning. The playability,
strength and harmonicity are calculated using an expert system developed by Botros et al.
(2002, 2006) and trained on the Acoustic Laboratory’s resident ‘expert’, flutist Jane Cavanagh.
The usage of ‘AnalyseNotes’ is
Usage: AnalyseNotes [OPTIONS]
Options:
-h (Displays harmonicity data)