Your typical signal chain is like this
Microphone, preamp, converter, computer.
Many recording interfaces streamline this process so that you don’t even realize the individual components because it’s all bundled together conveniently in one box. Simply plug a microphone into the mic input, and it is automatically routed to the preamp, the converter, and to the computer.
If you use the line inputs of an interface, it will bypass the preamp, and the signal chain will look like this
for instance, if you are recording the output of a keyboard, this output is already at line level, so it doesn’t need to go through a preamp, therefore, it gets plugged into the line input, which goes straight to the converter.
If you are using an external preamp, it will get connected the same way as a keyboard, and get plugged into the line input.
If you are recording a microphone, the signal from the microphone is very weak and needs to be amplified, and therefore needs to go through a preamp, which will boost the signal to line level.
so the signal chain will look like this,
Microphone- Preamp input. Preamp output to the line inputs of the interface which goes straight to the AD conversion.
Guitars have a unique output called Hi-Z, or Hi Impedance. This is a very weak signal similar to a microphone signal, but it is unbalanced and the electrical resistance is not optimized to be plugged straight into a preamp. So, a device called a DI box is used which converts the guitar signal to a balanced signal with a lower impedance which gets plugged into a preamp, just like a microphone.
so the signal chain looks like this,
Guitar to DI box. DI box xlr output to preamp. Preamp output to line input of interface, which goes to the conversion.
Some interfaces and preamps have a hi-z input, which is basically a DI box built into the preamp for use with guitars. So if the preamp has this, then it is not necessary to use a separate di box.
If you have an external FX unit, such as a hardware compressor, the signal routing will be as follows,
Microphone - preamp- FX unit- Line input of interface
Since the FX unit must come after the preamp, many interfaces offer a send/return feature to accommodate this, which I explain in the next video.