SP395 SoundPro Audio Integrator Form7492 Operation Manual
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For example, if you want to create a waterfall graphs to show the decay pattern for a room, you
may want 10 sweeps, spaced out in 50 mS steps, to examine the first 500 mS of sound decay in
the room. In that case, you would select 50 in the Sweep Delta field and 10 in the Sweeps field.
If, for example, your room has a long decay time, you may want to examine a longer decay time
in the room. You could create 10 sweeps that cover 4 seconds by selecting a Sweep Delta of 250
mS. Each sweep would then have an additional 250 mS delay from the previous sweep.
Filter Q – The Filter Q field controls the steepness of the band-pass filter. A higher Q results in a
filter with steeper slopes. In most cases, you will want to use a high Q value. A lower Q might be
used to create a smoother curve, to see the big picture more easily. However, more information is
shown with a higher Q filter.
Note also that the SP395 TDA function uses a constant-Q filter. Other TDA platforms work with
the equivalent of a constant-frequency filter. Constant Q can result in fewer problems with
comb-filtering.
Space Equivalent Bandwidth – It is useful to be able to control the distance beyond which
TDA will reject input. In some systems this is called “time windowing,” referring to the time that
it takes reflections to bounce off room surfaces. In TDA, we define a distance, called the “space
equivalent bandwidth” (SEB). This distance is defined as the distance beyond which input is
attenuated by at least 3 dB. This distance is a function of sweep speed and filter Q.
For example, with a Q of 36 and a sweep time of 8 seconds, the SEB is 7.3 feet. Thus, if your
speaker is at least 7.3 feet from any other surface, the test results will effectively remove the
effects of the room from the measurement. In fact, since the filter decays very rapidly, in many
cases you will get good results at up to twice the SEB.
Also, the shorter the SEB distance, the more the rejection of spurious noise.
Space Equivalent Bandwidth is computed on the Setup screen and changes as you change the
Sweep Time and Filter Q.
The formula for SEB is as follows:
SEB = B * [ c / (df/dt) ]
Where B is the filter bandwidth in Hz, c is the speed of sound, and df/dt is the sweep rate of
the filter in units of Hz/sec. The units of SEB are the same as the distance units used in the
speed of sound.
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