Lake Controller Operation Manual

Lake Controller Operation Manual Rev 1.6.1
Analyzer Plug-in
217
18.4.3.3 Spectrograph Properties
The Spectrograph measurement mode is controlled by all of the settings under Spectrum Properties, as
detailed in section 18.4.2 on page 213.
18.4.4 Transfer Function Measurement Mode
The analyzer’s real‐time Transfer Function measurement capability is a useful tool for setting up sound
system equalizers and crossovers. The Transfer Function is calculated by comparing the signal on input to a
system (reference) to the signal on the output of the system (measured).
By comparing what goes into a device or system with what comes out, the transfer function calculates its
frequency (magnitude and phase) response very precisely. A major advantage of this dual‐channel approach
is that it works with a wide variety of test signals, including music or other recognizable program material.
To make a transfer function measurement, a test signal is split at the source and sent to both the system
under test and back through the analyzer as a reference signal. The output of the system under test is
returned to the analyzer as the measurement signal.
Figure 18-11: Block-diagram of Transfer function measurement
In Transfer Function mode, calculations are performed using audio data from the two inputs. This data is
compared and displayed as a single trace showing the relative magnitude difference between the two
signals frequency by frequency.
The default Transfer Function mode Magnitude display plots magnitude values on the y‐axis with 0 dB in the
center and positive and negative decibel values above and below the zero line. The x‐axis of the plot shows
frequency and is normally displayed in logarithmic scaling with grid lines at octave intervals. On the standard
magnitude display, a value of 0 dB for a given frequency data point represents an equal amount of energy
(that is, a relative difference of zero) in both the reference (system input) and measurement (system output)
signals at that frequency. A positive or negative decibel value for a given frequency indicates more or less
magnitude in the measurement signal relative to the reference signal at that frequency. The Phase display in
Transfer Function mode is a second plot showing the relative difference in phase between the two signals
for each frequency.
In most cases there is a distance between the loudspeaker and the measurement microphone. This
distance creates a propagation delay (the sound travelling through the air) which must be compensated for.
When a transfer function channel is started a reference channel must be selected. Press FIND to nd the
delay so the reference signal can be adjusted to the same delay.