ACID files and REX files are practically the same thing, and can be used in pretty much the same way. No need to repost the description, just read What is a REX file

The only real difference between them is that some files that claim to be ACID files aren’t sliced into beats, where all REX files are.

REX files and ACID files, in the simplest terms, are audio loops. They have some extra formatting that makes them REX or ACID files, though.

REX files are created using a program from Propellerheads called ReCycle. That’s how it gets it’s name; REX = REcycle eXport. The ReCycle program is dedicated to creating REX files for use in other programs, such as Reason’s REX player, or directly in an audio program that is capable of utilizing this functionality, such as the current version of Pro Tools.

ACID files are basically just WAV files that contain “extra” information about the WAV file. Information such as tempo, length, and a beatmap are usually included in the “extra” information. Some ACID files (especially older ones) exclude the beatmap information which makes them useful in other programs (like Pro Tools), and only include tempo and length information. ACID files are created using a program from Sony called, well, ACID. ACID can be used to create acid files, but the program itself is also a detailed and complex looping DAW of it’s own. There are other programs that can be used to create ACID files, such as Sony’s Sound Forge, and a few other third party programs.

What these programs do is turn a regular audio loop into a REX/ACID file by separating the loop into smaller pieces, usually on the individual beats within the loop. This process is called “slicing” the loop. REX files and most ACID files can be and are considered “sliced” loops.

REX/ACID file usage all depends on the functionality of the program you are using them in. Some programs, such as Reason’s REX player, allow you to trigger each slice in the files with a MIDI event.

Some programs (such as ACID and Ableton Live) do not require the slice data, and only go off the tempo and length information to “warp” the file to conform to a specific tempo.

Some programs, such as Pro Tools, allow you to use the file in a tick based audio track, where the slices lock to the beats in the track, and follow the tempo of the song if/when changed. Programs like this also allow you to cut/copy/paste individual slices anywhere you like.

The term “insert” comes from the analog audio world, and refers to a physical point in the audio signal chain where a “detour” in the signal chain can be “inserted”, usually by means of a TRS (tip-ring-sleeve) jack and a “Y” cable. It is typically used to “insert” effects into the signal chain.

Pro Tools uses this concept of “inserts”, both for plugin functionality, and hardware effects.

Auxiliary(AUX) Inputs are tracks that pass audio through them without the need for the audio passing through to be recorded. They can be used as returns, sub mixers and bus masters.
An example of aux track use would be a drum sub mix, where you would bus the outputs of your drum tracks to a stereo aux track and control the overall volume of the drum kit with the stereo aux.

Another example of aux track use would be when using external synthesizers and/or sound modules with Pro Tools. The outputs of the synthesizers can be routed to and through aux tracks, and since you are controlling them with MIDI, and bounces contain any audio passing through the default outputs, there is no real need to necessarily record them to audio tracks.

There are many different uses for aux tracks.

It’s a big yellow vehicle that carries children to and from school…

But seriously, a “bus” in audio refers to the path between two points. It’s a holdover from analog hardware, where a “bus” is actually a physical wired connection. In fact, the school bus is actually a good analogy; the school bus carries children from one place to another, and the audio bus carries audio from one place to another.

There can be many different busses. You will probably hear the main outputs, the left and right components of a stereo signal, be commonly referred to as the “2-bus” or the “Master Bus”. It is the “bus” that carries the main two channel signal (hence “2-bus”).

Pro Tools, and other DAWs, use busses to route audio internally. Pro Tools uses the term “bus” for any audio path created and used entirely inside the software, and can use the busses to route audio from one track to another, or split the signal from one track to another, or any number of other uses.

s In very simplistic terms, you could refer to an audio bus as “how to get audio from one place to another”.