This is my experience on the Roland FC-300 midi controller as my Bass Rig manager. The reason I write this, is the utter lack of clear information about the capabilities of the patch mode, which I think is the best one for controlling multiple midi controllable devices at once.
My goal is to control 4 systems with it; POD HD500x, HX Stomp, Disaster Area DPC-8EZ and Source Audio Neurohub (connected to C4 Synth, Atlas compressor and AfterShock Bass Distortion).
I update this post as I go, so if there are questions, feel free to ask them in the comments, and perhaps I will find you an answer!
CHAPTER ONE: Number of simultaneous midi messages per patch
The manual about this is very vaque. It says something like "in theory one patch can go up to 500 bytes, but in practise it´s not that high..." which says absolutely nothing definitive even after I googled "how many bytes is one midi message".
Well, the answer to the question is: On the ON Stream FC-300 can send at least 33 PC and CC messages combined, and it still can go higher. But while testing it I just didn´t have enough energy to make up anymore messages, and I think thats more than enough for an average user.. My method of testing was to create one PC message for all 16 midi channels and then do the same with CC messages, ended up making 17 of those, one with channel Tx.
The OFF Stream seems to be the same, but I only added 16 PC (one per channel).
But I think there is some limit with all of the patches, as in if all your patches need more than 30 messages, there might be some limit after you can´t add anymore. I base this on the manual saying the FC-300 has 8kbytes (8000 bytes) of memory allocated for patches. And after my quick googling of the midi message size it seems that one message is about 3 bytes, thus with my untested math says average patch could have something like 26 messages each. 26 times 3 times 100 equals about 8000. Please don´t quote me on that, I don´t really know about these things..
CHAPTER TWO: Midi Transmit Channel
This one can once again be confusing, and may cause some people to ditch this unit before even buying it even though this is quite a useful setting for some users. THIS IS NOT A GLOBAL MIDI CHANNEL setting when we talk about Patch mode!
When writing a patch midi messages, you have a choise of channels 1-16, and then there is Tx. When you choose Tx, the message is sent to the channel you´ve chosen on the Midi Transmit Channel setting. This is useful when you, for example, have trillion patches already made, but for some reason you need to change the channel on the device you wish to control. If you have the Tx channel selected on those trillion patches, you can change all of them at once by changing the Midi Transmit Channel setting. This of course works only if you need one channel to be controlled or changed.
Thing that would be cool (but also maybe overkill) is if there was 16 (or just more than one) different Tx-channels (Tx1, Tx2, Tx3....) so you could have multiple "globally" changeable channel selections. But that is not the case, so I´m not gonna waste anymore of my nor your time by scribbling about it.
CHAPTER THREE: Power of Expression Pedals
Expression pedals on the FC-300 can be very powerful tools. In patch mode they can be programmed to control up to six different parameters at once, all in different channels.
In my case, I'm mostly going to use the Expression 1 for wah on the and the Expression 2 to control Parametric equalizer on the HX Stomp as a Low Pass Filter. These won't require much in the means of programming, basically just one CC per pedal (hindsight thoughts here).
But there is one oddity in my arsenal, where the extra programming power comes in handy. My goal is to have smooth transition between two completely different tones (octaver synth and heavily distorted "normal bass"), so I need to send CC:s to C4 synth to control Dry/Wet knob, Aftershock BD blend and output, and also to Pod HD500x to set the octaver mix knob. That makes four CC messages. If everything goes as I expect, maybe there will be a video clip here to showcase the thing. :D
CHAPTER FOUR: Expressions and Complications
It seems that there is a thing called "Active sensing" or "running status" property in the midi world. If I understood correctly, it means that if consequent messages are sent on same channel and same CC (like when the value on the expression pedal changes when swiveled) the midi message sent is trimmed shorter by cutting parts of it out to make the data flow lighter.
Some gear seem to not like that, like my HX Stomp. The way this problem manifests is, that the parameters that the expression pedal is supposed to controls behave irratically, skipping numbers and working unevenly.
I have not found a way to disable this behavior from FC-300, but I found a solution on the Line6 forums. I just need to make the expression pedal to send two different CC messages on different channels, and it negates the "running status" problem. Not perfect solution in that it means little bit more programming, but the expression works perfectly now. Here's an example of how smooth the pedal is when this fix is applied:
CHAPTER FIVE: Mystifying behavior of RC-300 Looper
This is quick note about something that doesn't really concern the FC-300 directly, but I had a strange interaction happening while controlling the Boss RC-300 looper pedal with the FC-300. Maybe this will help someone with similar problems with same or other equipment. Let's get into it!
I programmed the RC-300 to trigger samples preinstalled in it's memory by sending CC#'s to it by selecting a patch from FC-300. The weird thing was that the sample triggered only once, and after that, the RC-300 never triggered anything via midi. I could press the buttons on the unit itself, and it worked normally. I also was able to send PC-messages from FC-300 to it and the RC-300 responded to them by switching patch numbers. After I rebooted RC-300 the same happened: One trigger and then silence. Here's how I fixed it: in the RC-300 memory settings, change the "Assing Source Mode" from Toggle to Moment. If someone understands why this happened, feel free to explain it in the comments!
CHAPTER SIX: Message restrictions on CTL3-8 and ExpToes
Even though the CTL1 and CTL2 are very flexibly programmable, as in you can make them send multiple ON and OFF messages all kinds of message types (for example CC's and PC's that I need), the CTL3-8 and Expression Toe switches are restricted to only sending CC-messages. This is a problem for my kind of system, because I need to send PC-messages to toggle some effect pedals on and off. Also the number of messages from CTL3-8 is restricted to one, instead of for example ExpToe's six possible messages. Luckily my friend had Midi Solution's Event Processor Plus, that I use to convert CC-messages on channels 6-10 to PC messages on channels 1-5 where my pedals are assigned. But still, it's a pain in the ass compared to being able to send what ever messages from the FC-300 itself.