Titanium's two walk talk feature works in two different manners depending on whether the model is a DVR or NVR.

NVR

NVR models with physical audio in and out ports allow for "global two way talk". Global two way talk does not get recorded and is not assigned to any specific channel. The function acts as two way talk to the NVR in general.

When an IPC has audio in/out capabilities you can connect a speaker and mic directly to the IPC. When set up in this manner you are able to two way talk using the "Channel two way talk". This audio is recorded and bound to the channel that the mic and/or speaker are connected to.

DVR

DVR models with audio in and out capabilities allow for general two way talk. The two way talk function is bound to channel 1.

The audio in port will correspond with the channel number of the analog cameras. You cannot reassign the audio channel. For example, audio in channel 2 will be bound to channel 2.

IP Cameras connected to a DVR will function with the same logic as NVRs: 
When an IPC has audio in/out capabilities you can connect a speaker and mic directly to the IPC. When set up in this manner you are able to two way talk using the "Channel two way talk". This audio is recorded and bound to the channel that the mic and/or speaker are connected to.