I've been wondering about all the variations myself so this post prompted me to do a little testing and I'm glad I did - it has revealed some very important info for anyone who uses the UA-5 as an analog unit (like me) or gives out an analog patch. Some implications for people who run meters on the analog outs as well.
Without the digimod, the instructions make sense:
monitor button on - UA-5 outputs (headphones/line outs) are monitoring the analog input signal (a>d---d>a)
monitor button off - UA-5 outputs (headphones/line outs) are monitoring the USB signal from the pc (which may end up being the UA-5 inputs but could have effects and other signals mixed in)
The digimod cuts the USB audio input path and connects the a>d output directly to the src/spdif chip. So the monitor button doesn't affect your digital outputs. I confirmed this by testing both optical and USB outputs. At the same time, the digimod puts the UA-5 permanently into 'monitor' mode because the signal was jumped over to the src/spdif chip, where it runs into the signal path that would be followed by a USB source (normally heard with monitor off). A trace cut could stop this but there's no reason.
What I hadn't considered is that the monitor button does still function, and from what I can tell,
it is adding a second layer to the analog output - this is very bad! Following the signal path, the monitor button 'cuts in' to the serial output of the main codec (a>d and d>a) and takes that digital signal, converts it to analog and runs it through all the analog outputs. These observations confirm that:
1.
monitor off sounds the same as the original source (I plugged my headphones from cd source to UA-5)
2.
monitor off sounds the same as
monitor on with the volume set at 0
3. turning up the monitor volume adds to the overall level but strips the high frequencies (likely from mixing a slightly delayed source)
4. the mono/stereo does have some effect when monitor is on
And through all of this, the 'output' pot also affects the overall signal.
So for me, who is sometimes using the UA-5 to feed into a separate a>d, I need to remember to keep that stupid monitor off and that the output pot acts as a kind of post-gain. I could calibrate the output so the peak light matches up with the meters on the pc but metering has never been a strong point on the UA-5
For people running meters off the analog outputs, the sound quality doesn't matter so I suppose you can calibrate it to anything as long as all the settings stay the same. Keep in mind you are always affected by the output pot, and if you have the monitor on, then your meters are also affected by the monitor volume and stereo/mono button. If you keep the volume monitor down to 0, then it won't matter if you have the monitor on or not. I'd probably calibrate to something easy like monitor off, output at full.
For anyone giving analog patches, although this seems backwards, if you have the digimod you actually want the
monitor off and then give them levels by adjusting the output knob.