Overview
Connecting your guitar to an interface is very simple, however, there are a few things you need to understand to ensure an optimal connection.
The output on your guitar is very dynamic which means it has a range from very quiet to very loud. Instruments such as guitars, bass, and digital keyboards, output a signal much weaker than a mixing board or audio interface. We refer to this output level as an “instrument level” output. This allows the instrument to have lots of headroom to capture all the dynamics of the pickups.
Digital audio interfaces and mixing boards operate at line level which is a measurement of amplitude (voltage). Line level ranges between -10dBV to +4dBu. This is a much stronger signal vs instrument level at -30db. In order to properly match your guitar to your interface, the signal needs to be pre-amplified/boosted.
This means if you are plugging your guitar into an interface with a regular line-level input, then you would have to boost the signal with the built-in interface preamp or with an external pre-amp.
Now luckily most interfaces today include instrument-level inputs. These are typically found in the very front of your audio interface and labelled by a guitar icon or also referred to as a Hi-Z input. This will automatically bring your guitar input to the correct level without having to use a pre-amp.
The mistake most beginners make is they will plug their guitar into an instrument input (which is correct) but then they will also use a pre-amp to boost the signal further. The issue with this is now you are overdriving the signal and introducing a digitally clipped signal into your amp simulator. This will cause the amp simulator to sound extremely overdriven in a nasty way and very flat.
How to Input Your Guitar into an Instrument Input (hi Z) on Your Interface
This is the easiest and simplest way to connect your guitar because as mentioned your interface will automatically bring your instrument output up to line level matching the input.
You will want to review your interface manual to ensure it is equipped with an instrumental level input (hi-Z) and make sure your guitar is plugged into the correct input. Usually, a guitar icon will mark the input and most interfaces with have some sort of indicator lighting notifying you of the connection. Make sure with this type of connection you do not have any input gain (pre-amplification) applied. That is it!
Now we can load our guitar simulator plugin, and you can see our input level can sit at unity and we have full signal. In some cases where you have a really hot pickup and the input gain is clipping, we can turn the input down slightly on the software side.
How to Connect Your Guitar to a Line-Level Input
Looking at the back of your interface, there will be inputs that accept either a mic-level or line-level input. Plug your guitar into one of these inputs and set the set the interface to line level. Now in this case because our instrument is a lower signal level than line level, we will have to use the built in pre-amp or an external one to increase the input gain to a higher level. You will want to do this by playing your guitar at the loudest volume you would be playing and increasing the input gain to the loudest point but not clipping (hitting the red).
We also want to keep an eye on our input level on our amp simulator making sure it is not clipping there as well. Once you find the balance, you are ready to go.
If you were running your guitar into an outboard pre-amp and boosting the signal there, your out-board pre-amp will be outputting in line level. In that case ensure your interface is set to line-level input but no built-in pre-amp gain is needed.
So in summary you always want to match the output signal of your instrument to the interface by either plugging right into an instrument-level input (no input gain needed, or line-level input (input gain needed).
