We think of HD as software today but it is principally a hardware solution. Pro Tools HD was introduced in 2002 and was discontinued in 2011. Although its fair to say that the pain involved in abandoning the interdependent hardware and software of HD to move on to new hardware extended the life of HD, for a computer system 9 years is an awfully long time. I wasn’t using HD systems prior to 2002 but the leap in performance represented by HD systems at the time was huge. For all of the debate around the relevance of hardware based DSP systems today, it is undeniable that Pro Tools HD was (and still is) a great product with an exceptionally long life. I use HD systems every day and in spite of a few idiosyncrasies, for music, tracking and mixing live bands, they still work brilliantly.
What is HD about Pro Tools HD?
The HD part of Pro Tools HD was ostensibly the increased sample rate. 24 bit recording was was introduced in 1997 in Pro Tools III, by 2002 the current high end Pro Tools system was the Mix and Mix plus systems which offered respectable IO and track counts but were restricted to a 48kHz sample rate. HD offered new hardware and clocking specifically designed to support sample rates up to 192kHz. Even all these years later opinion on the importance of recording at high sample rates is divided but its easy to forget the enthusiastic rush towards high sample rates which was prevalent at the time and with consumer soundcards proudly displaying their 96kHz credentials, its understandable that a a professional system like pro tools had to get on board.
Timeslots in TDM 2
A major limiting factor in older Pro Tools systems was the TDM buss, the original TDM buss offered 256 timeslots in total. HD increased this to 512 timeslots per DSP, removing a major limitation. Of course all of this change necessitated expensive hardware upgrades similar to the change from HD to HDX and the hardware change didn’t coincide with an major version change of the Pro Tools software - Pro Tools 11 is incompatible with HD hardware. The transition between Mix 24 and HD happened between 5.2 and 5.3 - hardly as big a change as v10 to v11.
No Latency, No Problem
Today the processing power of an HD system often isn’t the main reason to buy one, leaving differences between software aside, marketing restrictions (IO, voice count, track limitations) apply but the principal advantage offered by Pro Tools HD hardware (i.e. things you can’t do running HD software without HD hardware) is the extremely low latency monitoring and the possibility of monitoring through DSP plug-ins. There is of course the halfway house solution of managing latency using interface-specific, dedicated mixer apps like those offered by Focusrite or UAD (and with UAD the possibility of monitoring through plug-ins) but working entirely within Pro Tools, HD or HDX hardware is the only truly low latency solution.
HD System, HD Software
The most visible distinction between HD and non-HD systems today is of course the software and so much has been said about the frustration felt by non-HD users at the arbitrary withholding of software features to drive sales of hardware that I won’t add to it here. We all know that HD software offers features which non-HD software does not and many people feel strongly that these features should be available to all without the compulsory purchasing of any hardware. For all its occasionally clunky charm - for example having to insert a TDM plug-in before it if you want to monitor through an RTAS plug-in or constructing cunning workarounds involving printing to a track in destructive record and consolidating the clips on that track to avoid a real time bounce, depending on what kind of work you do, Pro Tools HD has facilitated so much work for such a long time that I think it deserves the entry for H all to itself.