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Acoustic pulse reflectometry was introduced in
section 1.5.2. Here we describe
the apparatus and theory used in applying the technique for the measurement
of musical wind instruments. The apparatus used was developed by Sharp
et al. [6,19,20].
An acoustic pulse or audible click is produced by a
loudspeaker and is directed down a cylindrical source tube and into the
object to be measured. The resulting reflections are then measured
and analysed to find the internal profile and input impedance.
Since we are sampling digitally, we receive information
on the reflections from the instrument once every sample (ie. once every
seconds where is the same rate).
The result is that information is obtained on the change in internal profile
at discrete points along the instrument's bore. The reconstructed bore
will therefore be approximated by a series of cylinders whose length is such
that the primary reflections from successive cylinders occur at the sample