Create an Instrument Track in Pro Tools
Select an instrument to be inserted on the track. This can be any soft synthesizer or drum machine.
Once the instrument is inserted it will activate the application automatically. Applications by Propellorheads, Native Instruments, Celemony and others use the ReWire plug-in to route the third party application into Pro Tools.
One activated, you will immediately be prompted to select an output for it to be used. If you are using Melodyne, for instance, you will most likely be using a monosource. In this case you can choose "Left" for the output.
If you are using an application such as Reason, you will more than likely use a stereo source. For this select "Left 1 and Right 2."
In some situations you may use multiple sounds sent to separate tracks. In most cases, however, you will use different instances of the plug-in so that it can be assigned to its own output relative to the corresponding track. For say, the first track/instrument, select "Left 1 and Right 2" and for the next, choose "Left 3 and Right 4." Continue this process for all additional instruments.