Created on 2012-11-09 00:54:00
Unless blocked by a capacitor or a transformer-coupled output, analog audio devices will have some (usually very small) dc component in their output. Typical dc levels (often called dc offset) are in the range of –20 mV to +20 mV.
The embedded audio in a digital signal can have a dc component as well. This is usually very low in level, and will vary with the applied dither.
The Constant Value digital signal is “digital dc” of an arbitrary value.
APx can generate sine signals with an arbitrary dc offset, if desired. This facilitates “dc in the presence of signal” measurements.
DC in the presence of signal measurements
APx can both generate stimulus signals with AC and DC components, and can measure the dc component when it is an offset in an ac signal.
Coupling: AC or DC
Input signals can be analyzed and displayed in one of two coupling modes:
AC coupling blocks any dc signal component from analysis, displaying results for only the ac components. As a consequence, AC coupling introduces a rolloff below 10 Hz. AC coupling is the default setting. For the DC Level measurement only, DC coupling is forced.
Note: Some measurements may require the insertion of a small delay before analysis, to allow for blocking filter settling after a transient (such as generator start).
DC coupling includes the dc signal component in analysis and display.
For the DC Level measurement, the APx system is DC coupled regardless of user settings.