Huron & SNAP Documentation

Generating Test Signals
↓ To create the *.INV file
Notes on Test Signals
It is possible to generate test signals to be
used by the Measurement Tool. Each test
signal file saved in the SIM (*.SIM) format
requires a corresponding inverted SIM file
(*.INV).
Given a test signal in a *.SIM file, the
appropriate *.INV file can be generated by
the Matlab function makeinv.m in the
examples/huronmat subdirectory of the
Huron CDROM.
THE ENGINEERING TOOLS
SIM File
FFT
Invert
Elements
INV File
Figure 62 — Creating an *.INV file for deconvolution
Several test signals are supplied with the Huron software.
These are white and pink noises, and a special variety of swept
sine waves. The test signals that appear automatically in the
Measure program's list are located in the measure subdirectory.
Any test signals (and their *.INV files) that are added to this
subdirectory will also automatically appear in the drop down
combo box.
The type of test signal used will depend on the particular
response being measured. The test signal should be at least as
long as the duration of the system impulse response to avoid
time domain aliasing; a good rule of thumb is to select a test
signal twice as long as the estimated response duration. This
should be checked after the measurement. The Measurement
confidence indication given by the program will also help
decide if the test signal is appropriate.
White noise test signals (wht_NNNk.sim) should be used with
caution when measuring electroacoustic systems containing
tweeter speaker drivers. Since these signals contain a large
amount of energy in the high frequencies. This energy can
destroy tweeters with a low continuous power rating if caution
is not exercised. If in doubt, use a low volume or switch to a
pink noise signal. White noise is the recommended choice for
measuring purely electrical or purely digital signal paths. While
these test signals sound similar to Maximum Length Sequences
(MLS) used in some other measurement tools, they will give
better results because their non-binary nature is less likely to
cause overshoot and distortion in D/A converters and
transducers.
Pink noise test signals (pnk_NNNk.sim) have a spectrum with
equal energy per octave. This has a 3dB/octave amplitude
HURON TECHNICAL MANUAL PAGE 201