Each input on iD48 has a switchable Pad, Boost Phase Reverse and High-Pass Filter. These can be switched on and off using the buttons at the top of each Mic channel in the iD mixer software.
More information about each of these functions and when you may wish to use them can be found below:
Pad - 
The Pad function reduces the level of this input by -10dB. This level reduction is done in the analogue domain before the Analogue to Digital converters (ADCs). The purpose of this is to reduce the likelihood of clipping the input if you are tracking a particularly loud signal by reducing the overall level, thus avoiding having bad-sounding distortion on your recording. The 'PAD' indicator for this channel will illuminate on the front panel of iD48 when this function is in use.
Boost - 
The Boost function increases the level of this input by +10dB. This boost is applied in the digital domain after the ADCs. The typical application for this would be when you are recording a very quiet source and you are still struggling to get a good signal level even when applying the full 58dB of gain fro the Audient pre-amps.
Please note that as this boost is done digitally, it will also raise the noise floor by 10dB as well so should only be used when necessary. If you are finding you are getting low level from a microphone, even at full gain, we'd recommend moving the microphone closer to the sound source if possible. Doing this instead of applying the +10dB boost as this may give better results and result in a less noisy recording.
Phase Reverse - 
The Phase Reverse will flip the phase of the input signal by 180 Degrees. This will typically be needed when two microphones are capturing the same sound source at the same time. If the two microphones are picking up the signal out of phase, when these are played together the two signals will cancel out.
This will typically occur if you are recording both the top and bottom of a snare drum at the same time, or if you are capturing both the front and back of a guitar amplifier, but can also happen due to mic placement in a spaced stereo pair.
High-Pass Filter - 
The High-Pass filter will remove frequencies from the input signal that are below 100Hz. This is done in the analogue domain before the ADCs. This helps to remove unwanted rumble and low-frequency noise from your recording.
Common uses of a High-pass filter are to help remove Kick Drum bleed into your drum overheads or snare/tom mics. It's also useful for removing floor noise, where vibrations from the floor are being picked up mechanically by the mic.