I have been thinking about a tech post on tempo synchronization for a while. I’ve concluded that there’s no way to write something that’s universally helpful. It’s possible, though, that some of the stuff I’ve come up with might help somebody else, so here’s my best shot at it. Some assumptions:

• You want to work with iPad-based instruments and hardware synths simultaneously.
• You don’t want to spend a lot of money on high-resolution master-clock hardware.
• You aren’t going to have a heart attack if the timing is off by .00000000072 ms. (If you doubt that there is anyone who *is* going to suffer cardiac arrest over such a thing, you haven’t been reading the forums I have — proof positive, if any were needed, that humans can elevate almost any technical question to the level of religion).

Looking at things from a slightly abstract level is helpful in figuring out what specifically to do. You’re going to need:

• A central, easily-tempo-adjustable source of MIDI clock data, OR
• Another way for your instruments to know what the tempo is and agree on it (yes, I’m talking about Ableton Link), AND
• A way to make sure that all the instruments get that data via some kind of data connection, whether it’s MIDI cable or internal iOS magic or WiFi or what have you, and maybe
• Something that will translate from one of those connection/communication systems to others if it turns out that some of your instruments will only support MIDI and others only support Ableton, or some other exotic combination of communications protocol and timing standard..

So now I’m going to run down a list of what I’ve considered and used. No doubt there are other things that work, and I’d be especially interested in hearing from folks who are syncing with OS/X or Windows-based DAWS or otherwise using laptops for more that musical-routing centers, which is what I tend to do.

Anyway:

• Because Ableton Link is now built into the majority of iOS music apps, I tend to let it run the show. If for some reason you want to drive things with an iOS-based MIDI clock, MidiBus works quite well. It is highly accurate, and self-corrects for drift.
• Within iOS, you can translate back-and-forth between Ableton and MIDI clocks using an app called LinkToMidi. The developers make all sorts of disclaimers about using it with software instruments that only support MIDI, but in reality I’ve had little trouble with that.
• Finally, you need something to translate back and forth between the iPad’s USB-based communications and MIDI connections. I use iConnectivity hardware for this — I’ve used both the iConnectMIDI2+ and iConnectMIDI4+ successfully (and, by the way, without laptops). They work very well for both audio conversion and clock routing. They can be challenging to configure, the more so because the documentation for configuration is very weak. There is a new configuration utility that incorporates shortcuts for common use cases, but may not be any better for people who have specific needs.

So how does that shake out for me, in a real performance? Typically I have two iPads connected to an iConnectMIDI4+. Both iPads are running LinkToMidi. The output from LinkToMidi is routed via the iConnectMidi4+ to hardware MIDI ports leading to the hardware instruments. The iConnectMIDI4+ also has a hardware USB port that can be connected to (eg) an OP-1 or other hardware synth that accepts MIDI-over-USB to provide it with MIDI clock.

As for syncing between the Link setups on the two iPads, there are a couple of tricks you could use. If both are sharing a WiFi network, Ableton Link takes care of this on its own. If WiFi is unavailable, you could make one iPad the “Link master” by treating the other iPad as a MIDI destination. That would mean that only Link-enable apps running on the “master” iPad would be able to change the tempo, but that usually works pretty well for me since I have a tendency to run all the rhythm-section apps on the same iPad anyway. Finally, and best of all, the “Missing Link” product by Circuit Happy offers central control over Ableton link tempo and provides its own access point, as well as an interface to USB-based midi and CV/Gate control. I think very highly of it, and the company’s tech support is second to none.

Eager for comments, advice, corrections, and war stories — that’s what the comments are for.

Where to find stuff:
+ midiBus is in the app store, described at http://ipadloops.com/ios-midi-clock-sync-generator-and-mon…/ 
+ LinktoMidi is here: https://alexandernaut.com/linktomidi/ 
+ The iConnectMIDI4+ is here:https://www.iconnectivity.com/produc…/midi/iconnectmidi4plus