“I’ considering a Pro Tools system, but I’m confused. What is the difference between DirectConnect and HTDM?”
DirectConnect and HTDM are very similar, in that behind the scenes they use the same basic Stream Manager technology. The audio is “streamed” in or out of the TDM mix environment by a single DSP, which can handle up to 32 mono or 16 stereo “streams” of audio. The difference is that HTDM Plug-Ins exist directly within the Pro Tools mix environment, and can make use of Pro Tools automation rather than using MIDI only.
DirectConnect supports stand-alone applications that can stream in or out of TDM, but they are not directly integrated as HTDM Plug-Ins are. Instead you must move between Pro Tools and other DirectConnect “client applications” when working.
HTDM Plug-Ins also let you use Pro Tools TDM-compatible control surfaces like ProControl, Control|24 and inexpensive MIDI controllers for parameter control, which is a major plus.