User manual version 1
AV dsp amp
The first echo is apparent at 5ms. Zoom in until you see only the anechoic
portion of the impulse response. Dragging the mouse, left-button down, from
left to right marks a zoom area. Dragging from right to left zooms out. Dragging
with the right button down pans the plot left and right.
Figure 10
Click truncate . Anything currently outside the display is drawn in grey and
“
”
not processed. You will notice that in the frequency graph a portion of the low-
frequency response is also drawn in grey. This is to remind the user that
insufficient information is available to make *any* correction below this
frequency. A way of obtaining quasi anechoic low-frequency measurements is
making close-up measurements. Working with such measurements requires a good
deal of interpretation but it is doable.
Important: Avoid making any corrections for which no anechoic data is
available. If reflections are included, they are guaranteed to dominate the
measurement at low frequencies, and you will end up making corrections for
circumstances that are highly specific to the room in which the measurement was
made. Power-response data can only be made in a proper echo chamber or
preferably, by collating a large number of anechoic off-axis measurements. A
reverberant measurement in a normal live room just won’t do.
The steps of loading and truncating data can be repeated at any time. This can
be particularly practical when combining close-up and far-field measurements
during the filter design phase. The window in Figure 10 shows the result of
this. The small knot of corrections made around 70Hz is based on close-up data
first loaded separately. The LF section of the test mule is quite smooth apart
from one internal standing wave.
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