When you are configuring an Analysis step in your sequence you have the choice between Relative & Absolute at the top of the Waveform bar. In this quicktip we will describe what these two selections are and how to choose which one is correct for your application.
Relative Response: is the response level divided by the stimulus level.
Example: If we have an amplifier that outputs in units of volts(V) to a loudspeaker and a reference microphone that is setup to record in pascals(Pa); then the units of the fundamental coming out of a Relative analysis would be Pa/V. One characteristic of this measurement type is that a change in the output level of the amplifier will yield the same response if the system is linear.
- Useful for sensitivity measurements e.g. microphone sensitivity in mV/Pa
- Useful for measuring gain e.g. amplifier gain in V/V
Absolute Response: is derived from just the response level and is stimulus level dependent. The units used on the display are derived from the input signal path.
Example: If we have the same hardware as the above scenario and make a measurement then the units pertaining to the magnitude of the display step would be in Pa.
- Useful for SPL measurements e.g. max SPL of a loudspeaker
- Useful for distortion measurements e.g. 10% THD at 90dB SPL
In application we would apply this knowledge by measuring passive loudspeakers with an Absolute analysis type so that we are representing only the sound pressure output of the device.
No matter your selection between the two types, it is important to note that the “Custom Units” control in the curves tab of the Analysis Editor must be disabled to notice the change between Absolute and Relative analysis.