Midi Merge device to increase Axoloti Midi Inputs

#1

I know there have been discussions on increasing midi inputs into the Axoloti, and different ideas around it, so I guess this topic is not new, but look at it specifically as a unit with multiple 5 pin din inputs and one 5 pin din output, Yes there are some midi merge units to purchase, but they are quite pricy and don't seam to be many options. But considering some of the work I have done learning to use midi with Arduino or similar dev board, somehow it seams as though it would not be too difficult to build especially if i just focused to begin with on CC and Note messages.
The biggest challenge I would see is getting the code right, to ensure the relevant data packages are kept together, and that you are regularly cycling through every input to look for messages.

Has anyone tried anything like this, is there something I am missing ?
:grin:

#2

I haven't tried it, but have been considering putting together a midi merge unit... but too many other projects on the go... so when I really can't live without it, I won't have it :wink:
The circuit doesn't look overly complicated at all... and I'd simply use code already written.
I like the look of this 4-1:
http://www.joebrown.org.uk/wp/?p=2917

Also at ucapps.de they have a lot of midi info and projects there... including this 2-1:
http://www.ucapps.de/index.html?page=midimerger.html

#3

I have had plenty of success in my studio just chaining things using MIDI Thru. The only advantage of merging is if you want to use the same channel on multiple controllers. Since many of the MIDI devices in the Axo can be set to look at different MIDI channels why do you need to merge the data? Just set up the midi/in devices in the Axo to look at the different channels your different controllers are using. Standardize on a set of channel assignments (this controller always on channel 1, this one on 2 etc) and it is easy to run things.

#4

Thank you for that information @Ersatzplanet. I am new to setting up multiple midi devices and now feel I totally misunderstood the thru and merge scenarios. I was under the impression the merge could still maintain channel assignments but reduced to one midi out... Are you saying this can be done using 'thru'... I am struggling with multiple controllers on different channels. I have sub-patches use a different controller on a different channel than the main patch and not sure I am understanding how to do it right as I've had somewhat 'hit or miss' luck getting the controllers recognized.

#5

The main purpose of merging is to "mix" two for more controllers using the same channel into one line. The typical use would be merging a keyboard with a sequencer, both using the same channel to control one synth. With MIDI thru the channels and assignments plugged into the device are copied and passed thru to the output along with the signals produced by the device. In some devices, if set to the same channels of some inputting signal, will merge them in the device. This is rare. That is why most keyboards only have an out. The biggest problem with merging is that the signal can be delayed by all the different devices on the chain. The first unit in the chain will be delayed the most.

#6

This is really good information! thank you again. It is funny how as much as we read and try to understand it sometimes takes just a few words with a down to earth example to make things crystal clear. :slight_smile:
Now...maybe this is for a different thread, but... I have controller patch objects, which map CC's to pots and toggles, etc, but Axoloti only allows me to assign one in the main patch... which is global. Is there a best method for assignment of controller patches (are they needed) when sub-patches are on a different channel than main patch?
(edit) @Ersatzplanet your quote "Just set up the midi/in devices in the Axo to look at the different channels your different controllers are using. Standardize on a set of channel assignments (this controller always on channel 1, this one on 2 etc) and it is easy to run things"... this is exactly what I am after.

#7

Thanks for your overview @Ersatzplanet, but I am not entirely clear how midi thru replaces midi merge. It is described that midi merge is setup to allow multiple controllers to one destination, with this in mind, I don't quite understand what gets lost in translation in merge that is gained by midi thru. Ultimately, the design of the code will be to check each port for a message, if there is a message check to see if it is a status byte, if it is then read the next two bytes and send the status byte, and the following two data bytes and send them through to the midi out, then move onto the next port and do the same. The main challenge I see is, 1 - what to do if I read the first byte and it is not a status byte, 2 - ensuring as it cycles through the midi inputs, that it does so in an efficient maner to not cause messages to back up and cause delays to the message arriving.
I have been reading up on a few home made devices and it does seem as though the 2 issues I described are a common concern, but there does not appear to be too much reference to what has actualy eventuated in testing, hence my desire to raise the post to begin with.
:grin:

#8

I don't think MIDI thru replaces midi merge at all. They are different. Midi thru just copies what is at the input and passes it along. Midi merge "mixes" the input signal together. The only way to control one device with two midi controllers is with midi merge or if one of two devices controlling the synth has a merge function built in (some sequencers have this to merge a keyboard controller with them). With Midi thru you can use one controller to drive multiple devices that are easy chained, but you cannot use two controllers on the same channel with midi thru. The main advantage of the Thru vs Merge is the circuitry for the thru is much simpler than the merge. The thru doesn't need to parse anything, doesn't care about note channels, it just mirrors the input.

In my midi setup, I ran multiple midi synths with one master keyboard that also was a synth. The keyboard went to a sequencer (a hardware MMT-8, and then to a midi patchbay and then to the synths (and back to the master keyboard's synth (a Mirage). In some cases there were chains on some of the outputs from the patchbay (I had a lot of synths at that time). The patchbay had merging for two of its channels but I seldom used it because the sequencer drove everything and did merging on it. I could be playing on a channel from the sequencer and play live keyboard thru the sequencer on the same channel and it would merge them. I had a channelizer on my keyboard out that could re-map its output to any channel (or multiple channels at once) and that made it much easier.

#9

I'd like to get one of these in the studio at some point:

Not cheap at all no (more expensive than an Axoloti), but man this could be quite handy.