A/D's will have likely have buffer circuit on their line-in's for isolation, but I wouldn't call it a pre-amp.

An interface mic preamp circuit having its combi XLR and TRS jacks separately wired will typically have a unity gain output stage to the input of which the center TRS jack of the combi input is wired (or switchable when it also serves as an INST input) and that stage in any case simply operates as an input buffer to the ADC by providing (along with associated input filtering) the low impedance output (either single ended or balanced differential) at the level which the particular ADC employed requires (typically ~2V fullscale). Effectively, the mic preamp's high gain input stage is being bypassed and only its output (buffer) stage is being used (as a line buffer). Many mixer consoles have such a configuration
 
An interface mic preamp circuit having its combi XLR and TRS jacks connected in parallel will typically have its input pad-able as well as its gain able to be regulated to near unity for providing line level input buffering for the ADC. Effectively, the mic preamp is being operated as a unity gain line buffer amp.
 
"Gain staging" is a popular term, sounds so professional.
 
If an interface has dedicated line inputs (in addition to or instead of combi inputs, like the TC Impact Twin has) then it is simple enough to connect outboard preamps to those. Otherwise, use the input pad/switch if necessary and keep the outboard preamp's gain and the interface's input gain as low as necessary to obtain a clean signal without overdriving the interface's input and clipping the converter. Simple really.
 
And in case anyone worries about pads on interface inputs, note that some very nice ADCs include analog and/or digitally-controlled pads on their inputs (AKM come to mind).
 

Goddard
 
"Gain staging" is a popular term, sounds so professional.
 
 

 
Thanks

musicroom

Goddard
 
"Gain staging" is a popular term, sounds so professional.
 
 

 
Thanks

I call it 'git your **** together!' I don't know how many times I've completely tossed a mix and started all over because I got antsy and started working before dialing in gain levels first. If you find yourself putting putting in gain through an effects plug-in, you need to sit down and think about it for a bit.

SuperG

musicroom

Goddard
 
"Gain staging" is a popular term, sounds so professional.
 
 

 
Thanks

I call it 'git your **** together!' I don't know how many times I've completely tossed a mix and started all over because I got antsy and started working before dialing in gain levels first. If you find yourself putting putting in gain through an effects plug-in, you need to sit down and think about it for a bit.

I'm quite certain he was throwing a p/a dig. He didn't like my preference and many others for wanting to bypass an interface's onboard pre. I am not the most technical musician songwriter in the big ole daw world. But a few simple principles help to keep my recordings from sounding too bad. One is to use as few gain stages in my signal chain as possible. Not saying it's a showstopper, but if I can avoid that, then I will. So yes, I do pay attention to the small things, gain staging being near the top of the list. 
 
Carry on
 
 

Nothing wrong with wanting to avoid a gain stage, nope, not at all. From a technical standpoint, it makes good, rule-of-thumb, sense.
 
Of course, musicians and creative types are [usually] opinionated Diva's, so you might want to take that bit of salt into account when reading someone's opinions.
 
I'd try looking for an interface that supports both line-in and pre-amps on different connectors. For instance, the Ultralite MkIII I'd suggested has two pre's. The pre's have a switchable 20db pad, and also can be set for direct instruments such as guitar (less overall pre-amplification, different impedance, etc.). Not so surprisingly, the user manual specifically says do not use these pre/inst combo jacks for line level input. You probably could manage to get away with it, but why?; and as the manual points out, you have 6 additional line level inputs in addition to those pre-amps, so use those line inputs.
 
 

Ruling out any audio interfaces (or for that matter any other DAW input gear like preamp + ADC units) just because the mic preamps aren't bypassed when using the line inputs, due to concern about minimizing the number of  gain stages in the signal path might seem a wise choice but in reality isn't necessarily so, and applying such a criterion as a general rule rather than assessing each potential interface individually is rather foolish as different interfaces will, unsurprisingly, differ from each other in various aspects including their input circuitry.
 
Just as an example, consider the line inputs on the low-budget Behringer "Ultragain" ADA-8000 mic preamp + ADC/DAC unit, where the line inputs are on combi jacks with the XLR mic inputs with which they are wired in parallel. Thus, signals applied to the ADA-8000's TS/TRS line input jacks are applied directly to the mic preamp (offering 60dB of gain), just like the signals from the XLR mic inputs, and then to input buffer/filter circuits for the ADCs.
 
So, absolutely no bypassing of the mic preamps in the ADA-8000, only switching of which signal, from the XLR or TS/TRS inputs, gets applied to the mic preamp. Very basic and relatively cheap to implement.
 
And yet, surprisingly for it low cost, the audio performance of the ADA-8000's line inputs is rather well regarded, standing up quite well against much more expensive gear having discrete or mic pre-bypassing line inputs. And notably, they are capable of coping with rather hot input levels.
 
But please, don't take my word (or the word of anyone else unless convinced of their technical competence and experience and lack of any commercial agenda). Do your own research and evaluation.
 
And yes, I'm well aware that the ADA-8000 has other issues (power supply, ADAT sync), but those are not relevant to the audio quality of its non-bypassed line inputs.

SuperG
 
Of course, musicians and creative types are [usually] opinionated Diva's, so you might want to take that bit of salt into account when reading someone's opinions.
 

 
Well said. Considering this for my signature line.  :)
 
 
 

Wanted to chime in a moment about round-trip latency.
When it comes to round-trip latency, not all units are the same (especially USB audio interfaces).
Yes, the latency from A/D and D/A converters is consistent... as well as the latency from ASIO input and Output buffers (at a given size).
But... the audio interface's driver uses a hidden safety-buffer.  This is the X-factor when it comes to audio interfaces.
The best performing drivers use a small hidden safety-buffer (RME, Presonus Audiobox VSL, MOTU).
Tascam USB units are notorious for using a large hidden safety-buffer.
Most drivers don't allow any user control over the hidden safety buffer... so you're SOL if the round-trip latency is high.
 
12-24ms total round-trip latency is too high to effectively play/record and monitor in realtime thru software EFX/processing.
Get that number down to 5ms... and it's a whole lot more practical.
 
Round-trip latency is only a factor if you plan to record/monitor in realtime thru software based EFX/processing.
ie:  Say you want to track a DI electric bass at 1am... and you want to hear the results (as you're playing) processed thru an AmpSim plugin like Ampeg SVX.
That's when you need low round-trip latency.
If you're not playing/recording and monitoring in realtime thru software based EFX/processing, round-trip latency is not an issue.
 
Playing soft-synths is dealing with one-way latency (playback)... and is very roughly half the round-trip latency.
 
If you're buying a new audio interface, IMO it makes sense to get a unit that provides low round-trip latency.
Even if you don't think you'll use it.  Six months from now... you may be in a different scenario.  If your audio interface has high round-trip latency, there's nothing you can do about it (short of doubling the sample-rate).

Jim Roseberry
 
12-24ms total round-trip latency is too high to effectively play/record and monitor in realtime thru software EFX/processing.
Get that number down to 5ms... and it's a whole lot more practical.
 
Round-trip latency is only a factor if you plan to record/monitor in realtime thru software based EFX/processing.
 
...
If you're not playing/recording and monitoring in realtime thru software based EFX/processing, round-trip latency is not an issue.
 
Playing soft-synths is dealing with one-way latency (playback)... and is very roughly half the round-trip latency.
 

 
Good info.