Frequently Asked Questions

What the heck is IAC?

The IAC driver is an alternative to standard virtual MIDI endpoints. Both virtual endpoints and IAC buses allow applications to send MIDI to each other on the same machine without any external hardware. The primary difference under the hood is that while a virtual endpoint belongs to the application that created it (e.g. only Lockstep can write to the Lockstep virtual output), an IAC bus shows up as both an input and an output to all applications.

As far as Lockstep is concerned, there is little difference between Lockstep (virtual output) and Lockstep IAC; the only difference is that some applications, notably Pro Tools, will only accept MTC on an IAC bus, not from a virtual endpoint.

Can Lockstep output LTC?

Currently, no. Converting MTC to LTC is a completely different challenge, with largely different usage scenarios, so Lockstep currently focuses on the more common problem of converting LTC to MTC.

Does Lockstep have any freewheel/jam sync?

No; Lockstep simply converts LTC to MTC one frame at a time. (Okay, technically, this isn't quite true; when Lockstep sees one frame of LTC come in, it schedules a frame of MTC slightly in the future, in order to compensate for the latency involved in processing audio. So Lockstep actually has something vaguely akin to a 2-frame freewheel... but it's easier just to say no.)

Why does Lockstep take a second or two to sync up?

LTC, perhaps surprisingly, does not include the framerate anywhere in its data stream. MTC, on the other hand does—to an extent. So Lockstep has to wait until it's received enough frames of LTC to be able to tell definitively what framerate is being received before it can safely start transmitting MTC. This can take as long as a full second, depending on where the timecode stream starts.

Why does 23.976 fps show up as “24 fps”?

MTC does not distinguish between film speed and video speed. So, e.g., 23.976 and 24 are the same MTC data, 29.97 non-drop and 30 non-drop are the same data, etc.—just progressing at different rates. Since Lockstep transmits MTC in continuous sync with incoming LTC, incoming 23.976 LTC will get transmitted as 23.976 MTC, even if the status display simply reads "24".