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Rob,

Just found your site through Google, reviewed the manual, and immediately pulled the trigger on a MIDI Expression iO. Looks like a fantastic product. Thank you.

I have a question reference the following extract from page 17 of the user guide on routing with the MIDI expression iO and the possibility of ganging multiple iO's together in standalone mode:

" When the MIDI Expression iO is powered by a USB charger or battery pack, the device
automatically goes into standalone mode. In standalone mode, MIDI from the MIDI in port is
merged with the pedal inputs and sent out through the MIDI Out port."

Suppose I have 5 MIDI Expressions iO's in standalone mode with the 5-pin MIDI out of #5 plugged into the MIDI in of #4, MIDI out of #4 to MIDI in of #3, MIDI out of #3 to MIDI in of #2, MIDI out of #2 to MIDI in of #1, and, finally, MIDI out of #1 to MIDI in of an iRig Pro Duo which is then plugged into an iPad.

1. Will the 5-pin MIDI out of #1 going into the iPad through the 5-pin MIDI input of the iRig Pro Duo contain the aggregate of all the MIDI messages sourced from the 1/4" inputs of iO's #5, #4, #3, #2, and #1?

2. If iO #1 in the above scenario is connected to a Windows PC via USB instead of 5-pin MIDI out, will that USB stream into the computer contain the aggregate MIDI messages of the other 4 standalone iO's ganged to iO #1 that's USB-connected to the computer?

2. If so, what is the practical limit on the number of iO's I can gang together in this way? Is this something you have personally tested?

Here's my application. I currently have a Boss RC-505 looper which I am using as a multi-track backing track player, a Boss GT-100 for guitar effects, and a Yamaha MFC-10 MIDI foot controller. That's a lot of big and heavy hardware and I'm looking to replace as much of it as possible with an iPad running Cubasis (or maybe OnSong), an iRig Pro Duo interface to get guitar signal and MIDI control signals into the iPad and one or more ganged (I hope) MIDI Expression iO's to interface a set of Yamaha FC-7 expression pedals and Boss FS-5U foot switches with the app or apps running on the iPad. The other option is to run ganged iO's into a Windows laptop running a full-blown DAW like Cubase with iO #1 being a USB connection to the computer.

I like the flexibility of running as many or as few expression pedals and foot switches as I like into an iPad or computer instead of always having a great big lump of a MIDI controller at my feet such as a Yamaha MFC-10, Boss FC-300, or Behringer FCB1010.

So, I'd appreciate your comments on the 'gangability'' of multiple MIDI Expression iO's to accomplish this.

Thank you.

John

Mystic368 wrote:1. Will the 5-pin MIDI out of #1 going into the iPad through the 5-pin MIDI input of the iRig Pro Duo contain the aggregate of all the MIDI messages sourced from the 1/4" inputs of iO's #5, #4, #3, #2, and #1?

Yes, it will.

Mystic368 wrote:2. If iO #1 in the above scenario is connected to a Windows PC via USB instead of 5-pin MIDI out, will that USB stream into the computer contain the aggregate MIDI messages of the other 4 standalone iO's ganged to iO #1 that's USB-connected to the computer?

Again, the answer is yes.

Mystic368 wrote:2. If so, what is the practical limit on the number of iO's I can gang together in this way? Is this something you have personally tested?

There are a couple of things to keep in mind. First, there is a limit as to how much data can be send down a MIDI cable, although I think you'd be hard pressed to hit that wall (theoretically 31.25 kbit / sec). The second thing to consider is in regards to latency. It takes about 1 millisecond for MIDI data to travel from the MIDI In to the MIDI Out. So in the setup you described, the MIDI data coming from io #5 will have a latency of about 5ms before going into the iRig.

I haven't personally tested the limits of ganging, but I'll play around with it this evening and see if I can get some measurable data for you.

Regards,
Rob

Rob,

Thank you so much for a quick response. In my application, I doubt the accumulated latency will be much of a factor. Thanks for investigating it.

To me, the value of your product is that you separated the brains of the MIDI controller from the objects that you step on to make things happen, i.e. switches and pedals. That means people can have their MIDI controller a-la-carte, so to speak. Just plug in as many switches or pedals as they need for a particular application. This is distinct from the monster floor-based controllers out there like the FC-300, MFC-10, FCB1010, etc which have a fixed, permanent foot print regardless of the number of discrete switches or pedals you actually need for a particular application.

In another post, I believe someone suggested a new product idea of a floor-based MIDI controller. What I would like to see is perhaps a scaled-up elongated brick-like controller 'brain' with no built-in foot switches or pedals that comes with the equivalent of 16 switch/pedal ports available on the module from just two high density connectors (DB25?), each supporting 8 input devices. The cables would be pig-tail type that break out from a single DB25 at one end into a set of eight 1/4" plugs that go into discrete foot switches and pedals the end user provides for themselves. The Boss FS-5U switches can be physically chained together as can the Yamaha FC-7 expression pedals. In this way, the end user can determine the foot-print of their floor-based controller for themselves. Of course, you'd have to figure out how smart your 'brain' needs to be. For example, the FC-300 can send out MIDI patches up to 500 bytes long containing mixed message types on a single pedal press. MIDI macros, if you will. The MFC-10 and FCB1010 can do something similar but on a smaller scale.

I'd imagine the metal chassis and mechanical switches of the all-in one floor controllers I mentioned are a significant part of the overall cost of a floor-based controller. I really like the idea of a scaled-up but compact controller brain with a BYOSOP (bring-your-own-switch-or-pedal) approach to the mechanical aspects.

Thank you for your time, Rob.

So I did some tests this evening to test the limits of the MIDI ports on the iO. I stated by calculating how many MIDI messages the MIDI and USB connections should be able to handle. They are summarised below. Note: Standard MIDI messages are 3 bytes. USB MIDI messages, however, are 4 bytes.

I then chained together 3 MIDI Expression iO devices as shown below and proceeded to do some tests. I plugged in single expression pedal into device #3 and set it to send a CC on channel 1. I mapped this to a fader in Cubase and messages had no problems traveling down the chain and moving the fader inside Cubase. Given that an input is sampled every 4ms, the cable was sending at most 250 messages / second which is well below 1,333—of course no messages are sent when the pedal is not moving.

I then changed the channel to ‘ALL’ which effectively sends 16 messages at a time and mapped the messages to automate 16 faders in Cubase. Which this test, the iO could be trying to send up to 4000 messages / second. Not surprisingly, this test saturated the MIDI cable, and while the devices themselves remained stable, messages where clearly being dropped and I would occasionally see erratic movements of the faders.

I then repeated the test, but this time plugging the pedal into the device #1 which is connected via USB. This time there were no dropped messages and faders moved fluidly.

In reality, you’d be hard pressed to breach that 1,333 messages / second limit. Even while using a keyboard and two pedals simultaneously, you are unlikely to come anywhere near that limit.

I hope that gives you an idea of what to expect.

Regards,
Rob

Rob,

Thanks for checking into this and I agree with your conclusion that, for all practical purposes, saturation is unlikely to be a concern in any sensible use case for ganged iO's.

What I am trying to achieve by ganging multiple iO's is something like a foot-operated mixer to bring certain track groups of multi-track backing tracks in and out either by volume fade or by mute/unmute.

Something like this wouldn't be too taxing, I'd imagine. This is assuming several tracks in a DAW like Cubase can be configured to listen for and respond in tandem to the same incoming CC value message.

Expression Pedal A on iO#1: controls fader levels on several guitar tracks using a CC value message on a single channel.
Expression Pedal B on iO #1: controls fader levels on the drum mix track and bass track using another CC value message on the same channel.
Expression Pedal C on iO#1: controls fader levels on all vocal tracks using yet another CC value message on the same channel.
Expression Pedal D on iO #2: controls fader levels on 'all other instruments' tracks using yet another CC value message on the same channel.

So, four different CC messages all on the same channel but only one actively transmitting at a time since I cannot levitate and I haven't developed more feet than two in order to operate more than one expression pedal at a time without falling on my arse

Of course, If I just wanted to do mute groups, that would just involve transitory toggle-type CC messages. That would let me kick off different versions/mixes of the backing track from a single open project file.