MOTM

Two points:

1. We have started discussing AC vs DC signals. 

AC usually implies periodic cycling or repeating of the voltage 
pattern, such as a VCO waveform. However, an envelope generator that 
normally puts out a transient DC voltage can put out an AC voltage if 
being repeatedly triggered from an LFO, for instance.

If a cyclic waveform is symmetrical around zero volts, it is pure AC. 
If not, it is AC with a DC component.

2. Think of DC coupled inputs and outputs as having the ability to 
handle DC and/or AC. They pass everything on exactly as it came in.

An AC coupled input or output will filter out the DC component in the 
signal but pass on the AC component. Apply a pure DC waveform to an 
AC coupled input and it will have no effect, because it is completely 
filtered.

Moe
http://www.hotrodmotm.com