> So it seems that you do not (cannot) bypass a recorder's preamps by going line-in with a battery box, and the line-in/mic-in distinction is just a sensitivity thing where the mic-in expects a quiter signal and the line-in a louder signal. Makes sense now.
Well ... no, you generally can't bypass the preamp stage altogether.[snip]
At first glance, I mis-parsed the reply above before realizing my error in misreading the ellipsis. So, in a well intentioned effort to clarify the good DSatz's intent (hope I'm not out of bounds), read that as a response leaning towards the affirmative-
(my paraphrasing)
"Well, that pretty much the situation... you generally can't bypass.." Basically a
"Well, yes."-rather than as a refutation of yates's summary-
"Well no.."[/semantics]
The take away
for practical purposes is that the most important factor determining which input to use is usually the output signal level of the source feeding of the recorder input. In simple terms, for low level inputs use the microphone-input, for higher level sources use the line-input.
Another practical issue is if mic power is necessary and available or can be switched for the input as required.
As noted by others, the input gain stage circuitry is pretty much the same although the configuration values of it change, which may alter its performance. So other than mic powering and gross sensitivity/overload-point changes, the more subtle question is the noise and distortion performance differences between the recorder’s input modes (may be two different physical input jacks or a mic/line switch of some sort), and playing that variability off the performance and output gain adjustment provided an outboard gain stage such as a preamp or attenuators on the mic if something like that is being used. That is going to vary by machine and best practice is usually determined by measurement, or experimentation, or following the established practices of others around here using the same gear, etc.
I have noticed that the specifications of the small recorders I've used indicate slight differences of input impedance for the microphone-input verses the line-input, but usually not enough to be significant IMO. But those who have a better handle on the electrical side of things are welcome to correct me on that if I'm missing something there.
[edit, see discussion of that below]