Do NPN transistors add a 0.7 volt (approx) bias at the collector to a very small positive analog signal (emitter to GND), -or- is the 0.7 volts just the minimum that a NPN transistor can show at the collector (given very small positive volts at the base)?
The base to emitter is a single PN junction, aka a diode, and so will show 1 diode drop (0.6-0.7v). The collector to emitter is controlled by the current flow through the base but will have a minimum “saturation voltage” even when that base current is “large”. That voltage is typically 0.1-0.3v.