User manual

Audio Analyzer
AM700 Audio Measurement Set User Manual
4-41
measured THD as set in the Target Value field editor (the starting and ending
frequencies are specified with the Frequency Start and Frequency Stop field editors).
See Figure 4-16.
Generator and Frequency Selection. In the General Controls menu, you can select the
generator to be used (from the Generator selection menu). You can also set the
sweep count. A 0 sweep count setting causes a continuous repetitive sweep. Specify
the sweep frequency range with the Frequency Start and Frequency Stop settings
and set the number of steps in the sweep with the Points field editor.
Target Value and Target Error. Target Value is the value the analyzer attempts to
locate as it sweeps the generator in the range specified by the Frequency Start,
Frequency Stop, Voltage Min, and Voltage Max settings. Target Error is how much
the acquired value can differ from the target value and be considered valid data.
When the target value is realized, the analyzer moves to the next specified
frequency and causes the generator to repeat the process for the next measurement
point. The points that are displayed in the trace are the level/frequency pairs that
actually produce the target input to the analyzer. For example, if you are looking for
a specific THD value, the target value does not appear on the graph — the
level/frequency pair that produces the target value does.
NOTE. Do not set the Voltage Min to 0 V or to the minimum possible dBu level.
Regulation must be able to find a frequency to determine that it has started.
Search Limits. The Voltage Min and Voltage Max settings are the boundaries for the
range of voltages that the generator operates over as it attempts to produce the
required target value. Set the limits to cover the expected response characteristic of
the device under test. If the device has gain, the input limits must be divided by the
gain to provide the correct output voltage from the generator to drive the device to
the target value. Knowledge of the acceptable input level range to the device under
test must be used to determine the acceptable limits. Setting the limits wider than
needed increases the search time. In particular, if the Voltage Max is set to a level
that can cause the device under test to clip or overload, Regulation may not be able
to obtain the Target Value setting. This is because if the device under test does clip
while the generator is being adjusted, the combined system will be nonlinear and
may no longer be monotonic.