Recording Line level through Inst. input

GeorgeYekcnir

New member
Hello folks,
So last night I did a silly thing. I began to record a line leveled source through an inst. input on my interface realizing moments later why the signal was so noisy and loud. I immediately switched the input switches to 'line' however I got a strange out-of-phase signal. I than restarted everything and it seems to be back to normal.. Did I harm my interface?
 
You have to test it with the different sources and see if the distortion has increased - MIC, instrument, line
 
Hello folks,
So last night I did a silly thing. I began to record a line leveled source through an inst. input on my interface realizing moments later why the signal was so noisy and loud. I immediately switched the input switches to 'line' however I got a strange out-of-phase signal. I than restarted everything and it seems to be back to normal.. Did I harm my interface?

If your descriptions are all accurate, it's unlikely.
What was the output device....the line level source?

Line level could be hot enough to seriously distort through an instrument level input, but I'm pretty sure not hot enough to damage anything.

Being pedantic, perhaps, but for something to be out of phase it has to be with reference to something else.
Two microphones at different distances from the same source would be an example.

Has the strange effect happened since?
If not, I don't think I'd sweat it.

Welcome to HR, George. :)
 
it seems to be back to normal.. Did I harm my interface?

Evidently not. The Line/Instr places a resistor in the signal path to attenuate the signal before going to any kind of amp. Basically, it is the same amp used for both Line and Instrument. If that amp is working for either then it is working for both.
 
Some types of 'line' level likely would do damage in an instrument input, some won't :)
 

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The inputs of any AI of any worth should be protected from external high'ish voltages. In fact this is virtually mandatory with a pre amp with phantom power since the coupling caps can, in certain circumstances, dump their charge into the input stage.

You are cool.

Dave.
 
The Line/Instr places a resistor in the signal path to attenuate the signal before going to any kind of amp.
I've never actually seen inside one of these things, but I'm not sure that's quite exactly how it actually works. The basic premise that they both use the same amp IS true, and like you said, if it works for one it pretty much must work for the other.

But I've been looking at a specs for a few interfaces lately, and I've started to notice that many of them seem to have slightly different gain range when you flip that switch. Like, the difference between Max and Min is smaller in one of the modes. A simple resistive attenuator before the amp wouldn't account for this. It also doesn't make good gain-staging sense. I'm starting to think the switch does something in the amp circuit itself. It probably does involve switching in a resistor - but that'll be somewhere in the feedback loop of an opamp, not before the amp.

I could be completely wrong on that, but honestly I'm not sure anybody gives even half a fuck, so....

The weird part is that as long as we have a gain knob, we only need that switch because users are stupid. There's no reason at all that a Line Input couldn't just have an impedance high enough for passive guitars. Then you'd just turn the knob up 9-12db more for the guitar, and you're ready to rock! But the people who buy these things don't understand any of it, so we end up with this sort of thing where the High Z input also automatically comes with that extra gain. So what if I need High Z and that gain is too much? ;)
 
"The weird part is that as long as we have a gain knob, we only need that switch because users are stupid. There's no reason at all that a Line Input couldn't just have an impedance high enough for passive guitars. Then you'd just turn the knob up 9-12db more for the guitar, and you're ready to rock! But the people who buy these things don't understand any of it, so we end up with this sort of thing where the High Z input also automatically comes with that extra gain. So what if I need High Z and that gain is too much?"

That's a pretty kettle of fish with worms in it Ash! First off yes, a line input COULD have an input Z of 1meg but the problem then is noise. The passive guitar only provides a shunt impedance of 10k at the best and much more if pots are adjusted. Yes, 'proper' guitar amps have 1meg input Z but they ARE noisy fekkers! We demand stooodio quiet of our AIs! Then, the AI input amps are not optimized for high impedance. The superbly low noise NE5534 would be rather poor as a HZ amp.

H Z amp with too much gain Ash? They do that ALL the &^%$ing time! Worse case was the very early F'rite 2i2. The problem seems to be that WE all know that even the wimpiest catalogue Strat chucks out enough level to get -18dB on the ole'puter but you might struggle to get it to hit -6dBFS?
Such a low gain instru' input is not acceptable the marketing guys seem to think and the result is a decent humbucker or active cracks the front end up.
Of course the solution is simple? Have a decent amount of gain and then a -20dB pad. Trouble is of course, switches and extra Rs add to sale price in a VERY competitive market! (it is btw very easy to make a ~10dB high Z attenuator, will post pic if anyone wants one)

Am going to try to find some AI schematics but they are pretty secretive!

Dave.
 
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