Keysight U8903B - Table 4-9 Analog;Digital;Bluetooth Analyzer > Functions > THD+N Ratio Menu

4 Audio Analyzer Measurement Functions
196 Keysight U8903B User’s Guide
THD+N level is defined as the square root of the sum of the squares of all the signal
harmonics components and noise amplitude, and it is expressed in Vrms. The THD+N level
can be computed as follows.
Table 4-9 Analog/Digital/Bluetooth Analyzer > Functions > THD+N Ratio menu description
Menu Description
Unit
Press the Unit softkey to select the measurement unit.
–dB
– ΔdB
–%
–x
Format
Press the Format softkey to select the format of the returned measurement reading.
–Off
Selecting Off will return the measurement reading without any formatting (raw value).
– Linear
Selecting Linear will return the measurement result by dividing the measured ratio by the reference ratio. The result is
returned in unit x.
–Delta
Selecting Delta will return the measurement result by deducting the reference ratio from the measured ratio. The result
will be returned in unit ΔdB.
Set to 0dB
This is only available for analog analyzer.
Press the Set to 0dB softkey to store the measured ratio as the reference ratio, and set the measurement reading format to
Delta.
Set result as ref. from Press the Set result as ref. from softkey to store the measurement result from the selected channel as the reference ratio.
Ref. Ratio Press the Ref. Ratio softkey to set the reference ratio value.
Precision
This is only available for digital analyzer.
Press the Precision softkey to enable or disable the precision mode.
Freq Lock
Press the Freq Lock softkey to select the searching method for the fundamental frequency.
–Auto
Selecting Auto will allow the U8903B to search for the fundamental frequency automatically.
– Gen Lock
Selecting Gen Lock will allow the U8903B to search for the fundamental frequency based on the generator frequency
value of the respective generator channel. You can select the generator channel by setting the Src Channel in the Meas.
Config. menu page. This Gen Lock method is only useful if you use the internal audio generator.
– Custom
If you have a known input signal, you can define the fundamental frequency value by setting the searching method to
Custom and setting the frequency value in Fund Freq.
Fund Freq
Press the Fund Freq softkey to set the fundamental frequency value. This setting is only available when Freq Lock is set to
Custom.
Analog Notch
This is only available for analog analyzer.
Press the Analog Notch softkey to enable or disable the analog notch filter. This filter is used to emulate the analog notch
filter used in HP8903B.
THD+N Level rms value of noise and distortion=