Pro Tools HD and HDX systems represent the company's professional product line. They rely on dedicated chips that aid audio processing, in conjunction with rack-mounted interfaces, which handle outgoing and incoming audio, MIDI, and sync connections. With the introduction of Avid's HDX line, HD ("native") interfaces no longer feature DSP, and this feature has been reserved for HDX only. HD and HDX systems utilise proprietary cables to interconnect with external units.