If the oscillator is at a remote site it can be left repeating a sequence continuously (or
hourly or daily etc) allowing a test to be performed by simply connecting an LA102 to the
other end of the line and waiting until a complete sequence has been received.
Alternatively it is possible to trigger a sequence by applying a DC signal to the LA101
serial input, allowing control from a simple switch or timer (see section 3.25).
7.5 Mixing Consoles Computer support software Mixing consoles
Testing a system with a large number of channels can be time-consuming despite the fast
automatic test sequences. The LA100 can test two channels with a single sequence and
can also hold up to 6 sets of sequence results in its non-volatile memory. This means that
results for up to 12 channels can be held in memory for later printing (see section 3.5).
To minimise the risk of storing the results in the wrong memory it is possible to make the
LA102 automatically store the sequence results in the next available memory, repeatedly
cycling through the memories (see section 3.20). A computer can be used for storing
large numbers of results on disk (using Lindos Support Software).
7.6 Filters and Equalisers Filter testing Equaliser testing
Filters and equalisers can easily be tested using an automatic test sequence providing the
filter passes the FSK frequencies (1650 and 1850Hz). If this is not the case then connect
the left channel directly from the LA101 to the LA102 and connect the right channel
through the system being tested, as described in section 3.13.
It may be necessary to change the printed graph format to ensure that the area of interest
is printed. This is easily achieved by setting configuration options E, F, G and H to
determine the graph width, fit, scale and height respectively, as described in section 8.4.
Similarly if an equaliser is to be tested at several different settings then configuration F2
should be set to make the vertical scale the same for each graph.
Some care is needed when testing very steep filters where a slow sweep (segment S) may
be needed to accurately measure the frequency response (see section 3.9 and 3.10).
Filters can also be tested by entering the inverse weighting of the filter into the LA101
and section 2.27 explains how to define a third octave user weighting curve. The
frequency can then be changed manually on the LA101 and the deviation from the ideal
filter response can be read directly from the LA102 display. Alternatively, a weighted
frequency sweep may be used, see section 3.19. For a very accurate measurement of the
filter’s response over a large dynamic range the user level segment (K) may be used, see
section 4.13.
Tolerances can be defined to test the filter’s response whether it is measured using a flat
sweep, a weighted sweep or the user level segment.
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7. Applications Advice
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