MidiBus review – MIDI clock utility from Audeonic

Download from iTunes App StoreMidiBus logo

Anyone remember when music technology meant hardware synths, drum machines and MIDI cables? OK, I’m being a bit flippant here because these technologies are still a very valid part of both live and recording contexts. However, if you do remember when this was all there was, then I suspect you also remember the times it didn’t work – and nobody could work out why.

Of course, we also went through the same head-scratching when we moved over to computers, with MIDI streaming in from these external hardware devices and, a little while later, MIDI data whizzing around inside the computer from one virtual MIDI device to another. However, virtual MIDI is now a pretty mature technology and, if you are lucky enough to use one of the top-flight DAWs on your desktop of choice, you can now safely (well, pretty safely) send MIDI data wherever you want, whenever you want. At its best, it is sophisticated, slick and, very importantly, keeps everything locked vice-like to a tempo dictated by whichever MIDI device within your system is identified as the ’master’.

The state of the (iOS) art

Now we have iOS and it’s cute, hi-tech, exciting and has lots to offer the performing or recording musician…. but its also new and, as yet, still in the spotty teenager stage rather than mature – energetic and thrusting – adulthood. And we all know what that means – it can occasionally be stroppy and unpredictable – and still nobody can work out why.

In terms of routing audio, things in iOS land are actually in pretty good shape. Background audio, Audiobus and, more recently, inter-app audio (IAA), while still not without their own particular limitations or quirks, are generally straightforward to use and they get the job done. But when it comes to MIDI? Well, let’s just say that there is still some room for improvement.

Audeonic's MidiBridge is a very useful utility app.
Audeonic’s MidiBridge is a very useful utility app.

There is not too much problem now in getting basic MIDI note or controller data into or out of most iOS music apps. So, for example, if you want to record MIDI data into your DAW app and then send it out to a virtual iOS synth or two, then that can usually be achieved without too much difficulty. And if you do get a little stuck, then perhaps something like MidiBridge – a very useful MIDI utility app by developer Audeonic – can help you establish MIDI communication between apps that might not otherwise be happy to chat.

However, MIDI is not all about note and controller data; it also serves a synchronisation function, allowing you to use one MIDI device to control the transport functions (start, stop, tempo) of other ’slave’ devices. In the days of hardware, a typical situation might have had a hardware sequencer acting as a master and being used to trigger a drum machine (playing drum patterns) and a synth (playing step sequenced or arpeggio patterns).

This is probably where the biggest problems still lie in iOS MIDI. Some apps provide MIDI clock sync support and some don’t. Of those that do, not all of them can serve as both master and slave with the user being able to configure which role they might play in a given situation (for example, Cubasis can only currently act as a master). And even when you do find a configuration that, in principle, ought to work (for example, one app acting as master and a second acting as slave), the teenager can sometimes kick in and things don’t always work. Perhaps your slave just refuses to start, starts only intermittently or, if it does start, their is some latency in the system and the timing between the two devices is simply not tight enough.

The solution, of course, is for Apple and every app developer to really get to grips with Core MIDI and to ensure these wonderful music apps we have available to us are speaking the same (MIDI) language when we need them to communicate. While this sounds like it ought to be a simple enough task (after all, a similar process has proceeded at some speed for audio), we still seem to be some distance from seeing this happen.

All aboard the (Midi) bus

There is, however, what might be a very useful little chink of light that has just appeared on the horizon; MidiBus. Like MidiBridge, this is the work of Audeonic and, also like MidiBridge, MidiBus is, on the surface, a rather unglamorous MIDI utility app that offers one (OK, perhaps two) basic functions.

The MidiBus Transport screen - simple but effective.

The MidiBus Transport screen – simple but effective.

In the case of MidiBus that main function is to act as a MIDI clock sync master device. And, so you can judge something about the quality of that MIDI clock sync, the second function is to provide monitoring of the MIDI data; you can see how the clock varies over time.

In use

Actually using MidiBus itself couldn’t be more straightforward. In the Transport screen, you can see all the currently running MIDI enabled apps in a list and can tap these to toggle them on as a destination for MidiBus to sent MIDI sync data to. If you engage ’play’ in the MidiBus transport controls, then MidiBus will start transmission.

DM1 is happy to accept MIDI clock data from any destination.
DM1 is happy to accept MIDI clock data from any destination.

What happens next depends upon the MIDI capabilities of the target apps and – the more complex bit of the process – the configuration of the MIDI settings within each of those apps. This is where the fun starts because there is little by way of consistency here and it can often take a little digging and head scratching to find the settings you might want. And, of course, some of that digging might be in vain as quite a number of iOS music apps cannot currently accept MIDI clock sync.

All this means, I think, that MidiBus is perhaps just a wee bit ahead of its time – but perhaps also a bit of a wake up call (kick in the a**) to the iOS music app development world – as there is a good number of apps that still need some work on the MIDI front.

That said, if you chuck MidiBus at some of those apps that do respond to MIDI sync, how do things work out?

Thesys will also accept MIDI clock instructions from an external source.
Thesys will also accept MIDI clock instructions from an external source.

To start my testing, I picked a couple of apps that offer support for receiving MIDI clock data – DM1 and Thesys – and, once I’d made the necessary settings within their MIDI configuration options, was easily able to get them to start and stop via MidiBus and they seemed to lock pretty well together in terms of tempo (although I know there are MIDI geeks who are way more sensitive to MIDI timing than me so this is something that you really do have to text for yourself). Having a pattern-based sequencer app like Thesys lock to a drum machine app is a lot of fun and, if you like to perform or compose using pattern-based tools, it’s great to be able to sync these sorts of apps together.

Flipping to the MidiBus Monitoring screen suggested that the clock data issued by MidiBus is pretty solid in terms of its timing with zero variation in tempo and low latency (about 0.4ms). This is obviously very welcome, although how tightly the slave apps respond is, of course, also dependent upon their MIDI coding, not just that of MidiBus.


MidiBus will provide you with data about the MIDI clock quality through its Monitor screen.
MidiBus will provide you with data about the MIDI clock quality through its Monitor screen.

Both Cubasis and Auria can generate MIDI clock data of their own so, assuming MidiBus’ monitoring provides an accurate means of observation, I was interested to see just how stable those clocks might be. The results were quite interesting. With Cubasis, the tempo variation averaged around +/- 0.7% and the latency around 0.5ms. With Auria, the tempo variation averages +/- 0.5% (although the reporting of it seemed a little odd) and the latency was 0.6ms. In both cases, I had no other apps running in the background and was just using a project containing four stereo audio tracks.

Clearly, if the data MidiBus generates from its Monitor display is accurate – and assuming that there are no other variables or data bottlenecks at play here – the clock data generated by MidiBus itself is more consistent than that of either Cubasis or Auria. If you are particular about your MIDI sync, MidiBus would be well worth experimenting with.

A test too far?

Just of the heck of it, I then tried a test that I fully expected to be problematic. I used Secret Base Design’s Apollo to establish a MIDI over Bluetooth connection between my iPad Air and iPad 3rd gen. I then closed my eyes, crossed my fingers and tried to use MidiBus running on my iPad Air to send MIDI clock data to DM1 running on my iPad 3rd gen.

Trying to transmit MidiBus clock data via Apollo to a second iPad proved to be a bit of a step too far for my iPad Air/iPad 3rd gen. combination.
Trying to transmit MidiBus clock data via Apollo to a second iPad proved to be a bit of a step too far for my iPad Air/iPad 3rd gen. combination.

The results were – perhaps as I had expected – just a little unpredictable. Sometimes DM1 would trigger and sometimes it would not. On other occasions, it would trigger but not match the tempo set by MidiBus. It would seem that – at present at least – that extra layer of communication involved in the transmission of the MIDI clock data was just a step too far. Clearly, however, there is some potential here and, as and when all the wrinkles are ironed out (wherever those wrinkles might be in this particular data chain), the prospect of an ‘iPad band’ all sync’ed together via MidiBus would be an interesting musical experiment.

In summary

As I suggested earlier, I think MidiBus is a much-needed and very useful MIDI utility app. Audeonic’s website has information for developers on how support for the library of code can be implemented in apps and suggests that it is not a difficult task. If that’s the case, then it would be great to see MidiBus act as a bit of a nudge in getting us closer to a more uniform, consistent and reliable MIDI communication environment under iOS.

At UK£1.99, MidiBus is unlikely to break anyone’s bank and, if you use independent MIDI apps such as drum machines or synths with step sequencer features as part of your music making, then MidiBus might be right up your street. As a means of locking those sorts of apps together – providing their MIDI implementation is up to it of course – MidiBus is a simple and effective tool. It might not be the most glamorous or exciting of apps to look at but, as one of those very useful utility apps that can help everything else run smoothly, MidiBus is well worth having to hand.


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    1. Brilliant, you’re getting better and better at this John; this was really informative, I learned a thing or two and you’ve saved me some very precious time with the testing!

      If I’m recording loops then I tend to use Loopy, the midi implementation is very good and I have no problem synchronising those apps that allow it. For the ones that don’t, I tend to set the internal bpm to be the same (if available) and just take, and re-take, till I get it right. In this sense I am unsure what use this app will be for me at the present time, but still it’s good to know – cheers!

      I’m interested to see if the library starts to be used, and if it helps developers who would otherwise find it too challenging to implement midi into apps that would otherwise probably never have it, if it pans out this is a very good thing!

    2. Miguel Marcos says:

      Beyond emailing individual app developers, I wonder what can be done to give some impulse to standardizing MIDI clock amongst the different apps on iOS. Checking out different app combinations can be so time consuming. I wish there some spot on the web where users could exchange info about what’s worked for them and what hasn’t.

      • Hi Miguel… I agree that MIDI Clock can be a bit hit and miss at present… which is why it would be so good to see MidiBus get wider support. The whole thing ‘ought’ to work…. but, sometimes, just doesn’t…. and it can be very frustrating…. Maybe this will be a good topic for a post at some stage :-) best wishes, John

    3. Paul Mason says:

      I have midi tracks in Cubase 5 daw that I would like to send to Cubasis on my iPad 4. All the on-line dialogue I’ve seen is about sending from Cubasis to desktop. Can anyone help with this? I am able to record midi to Cubasis from my Roland RD300 GX via iRig midi 2, so I hoped that playing the daw tracks thru the Roland to Cubasis might work. I also came out of the midi out in the back of my Focusrite Sapphire Pro 40 and into the iPad with no success.
      Can anyone help with this?

    4. I’ve been a beta tester for various iOS music apps that support MIDI Sync.
      While CoreMIDI has some issues (like some long SysEx messages cut in the middle), nothing has kept developers from implementing near-perfect MIDI sync since iOS 4.2.
      Since there is a number of apps out there that did it right quite from the beginning (MoDrum, thor, StepPolyArp, MidiPatternSequencer, Thesys, Egoist, Genome, Molten, FunkBox etc.), it’s clear that it is only up to the developer to do it right.
      And MidiBus won’t ever be able to fix anything about a bad MIDI Clock implementation in any app.

      I believe that the most critical issues are the following:
      1. Understanding how Midi Clock Master and Slave Sync really works
      2. Giving Midi Clock first priority in the code, then audio, then UI
      3. Doing proper clock averaging for incoming MIDI Clock to avoid “jumps”
      4. Proper testing of the app in combination with different hardware and software.

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