A confusing area for novice Pro Tools users is the distinction between the choice of “interface” or “bus” when selecting inputs and outputs for audio tracks.
The term “interface” relates to a piece of hardware that is essentially outside of the Pro Tools system (computer), but is plugged in to the input or output of the software.
For example, an input interface could be a mixing panel or a microphone adapter box that would send a (line level) audio feed into Pro Tools so that it could be recorded. The microphone would plug into the XLR input of the outside device, and the device would send a proper output signal to the audio track in Pro Tools. Note that the volume level of the mic is set by the controls on the device itself, and not within the Pro Tools software. The fader on that audio track in Pro Tools only affects the output or playback level of what was recorded, but does NOT raise or lower the live recording level. To raise or lower the volume of the live microphone, you need to adjust the fader or knob of the hardware device itself.
Interface inputs could also be any special signal processor, feeds from other decks, or other outside sources of audio.
Interface outputs include an amplifier (feeding monitor speakers or headphones). It is not uncommon for a Pro Tools simple setup to use the computer’s built-in amplifier feed, but because the computer amp is NOT software and is outside of the Pro Tools software — it is considered an interface. Other interface hardware could be any physical device that receives and processes the raw signal from Pro Tools.
Busses, on the other hand, are not physical pieces of hardware. They are pathways to route signals within Pro Tools between tracks. Think of them as patch cables, or pipelines.
You can use a bus to connect the output from one track to the input of another track. A bus can serve as a dedicated pathway from just one track to another; or it can work as a hub to allow multiple tracks to flow into a single (or multiple) other tracks. For example, say you have ten audio tracks that represent all of the individual drums and symbols of the drum kit — but you would like to send them to an Aux track so that you could control them from just one fader, or apply the same signal processing to all ten tracks. All ten outputs would be assigned to the same bus number. Then you would assign the input of your Aux track to that same bus — allowing it to hear those ten outputs.
Bus numbers in Pro Tools are random; it does not matter which number you select so long as you are consistent with using the same number or name for outputs and related inputs.
To set up a different pathway, just use a new bus number. Inputs and outputs are only directly shared by tracks sending out to or receiving from the same bus number.
Sometimes, you want the audio output from a track to go to more than one target. For example, you might want to be able to hear a track directly, so the output may be the default audio amplifier interface. But you can also use the SENDS to simultaneously route the raw audio somewhere else in Pro Tools. It is also possible to create two or more OUTPUTS instead of using one OUTPUT and a SEND.
In summary, the main thing to remember is that INTERFACE refers to a physical piece of hardware outside of the software; and that BUS refers to your own virtual web of interconnecting elements within the Pro Tools system.
Read more about interfaces and busses at this excellent article on the web:
