1kHz 5VAC summed with a 5VDC signal using an inverting amplifier.
The result is an alternating 1kHz waveform being off-set by the DC signal which pushes the signal to alternate between the -5V peak point instead of the 0V point.
To solve DC off-set problems (especially for digital audio) the DC input voltage has to be measured then attenuated in order for the waveform to alternate at the 0V point.
