Erae II Touch USB Device port vs. USB Host port?

Erae Touch
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I’m having a hard time understanding the difference of these 2 ports? I can use the device port to send midi to my rack and it works fine. If I do though, I can’t use that port to interface with my computer. I would assume the Host port would also send MIDI to my rack in the same wave as the device port but it doesn’t work. I tried to route the MIDI device port to the host port but that doesn’t work either.

I would’ve thought the MIDI USB Host port would be the one I connect to my computer, but my Mac Mini doesn’t recognize it.

If anyone understands the specific use cases for these different USB MIDI ports, I’d love to know how to think about them.

Thank you!

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so a usb host is a device/computer than can 'host/have usb devices connected to it.
e.g. like you computer (usb host) , you can connect midi keyboard to it (usb device)

so… erae 2 is a usb midi device when you connect it to the one with computer symbol
note: a usb host can supply power.

the other (host) port is for erae to act as a usb HOST ie. so you can connect other USB MIDI devices to it.

as for working with other devices, well that depends what the other device is…
if its acting as a usb device, then connect to host port (most common)
if it is acting as usb host, then connect it to the device port.

frankly, this always confused people and usb-c has made it worst by insisting on using the same hardware connector … before we had usb-a and usb-b.
usb-a connects to a host, usb-b connects to a device !

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I really appreciate this! I had to read it 5 times for it to click, but I think I understand now.

I got confused because I think of my computer as a host and thought the host port should connect to the host computer but I get it now.

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It does make me wonder why it didn’t work when I routed USB Device → USB Host Port or MIDI-> Host Port in the hardware settings in the Erae. I was assuming the MIDI coming out of the host port would be the device output but it didn’t seem to work that way.

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yeah. unfortunately, this is always confusing to discuss because with any particular connection one is the host, the other is the device…
sometimes, this can be unclear in menus etc,

also the fact that for both sides, the connection is bi-directional. i.e both device and host can send and receive messages.

this really just a bit of a midi oddity…
e.g. no one confuses that a usb SSD is a usb device, and it connects to a usb host :slight_smile:

I’ll also say, that unfortunately, many electronic “music instruments” are hosts, when they would be better off as devices - this is due to the MCUs they use, rather than for ‘good reason’ :wink:

not sure about example you state, but its easy to get things around the wrong way, but once you clear up the understanding, its should all make sense.

the best bet , on the Erae is to see the computer symbol, and remember that a pc / computer is always a HOST. and a host always has to connect to a device (never a host)

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I’ve never thought about it that way before, all the devices I have that can act as hosts do so for good reason, and I wish more had that feature.

By this I mean that most devices I have which have host ports tend to be synths or grooveboxes/DAW equivalents/sequencers and it is desirable to be able to connect them directly to other USB equipment that can only act as devices, without requiring some additional device that can act as a host to be part of the wiring.

So I suppose I am curious as to examples of the sort of device you mean that only happens to have host functionality as a side effect of its underlying architecture.

I also like the fact that quite a number of the devices that have host ports support connecting a hub to the host port and then attaching multiple devices to the hub, although some dont.

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Admittedly, Erae is a rare example of a MPE controller that has a host mode. I think the only other one I have like that is the Push 3 Standalone, and host mode for that has more obvious use cases due to the other stuff that Push 3 offers beyond being a MPE controller.

The typical scenarios where I find a host port very handy are for direct USB connection of controllers that can only act as devices to synths, sequencers, grooveboxes that do have host functionality. Not that there are too many traditional hardware synths in that host category, the Waldorf Quantums and Iridiums are the mainstream expensive one that springs to mind. Having a controller that can act as a host would be very handy for direct USB connection to all the other synths that can only act as devices.

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Is it right to say that host port has all the functionality of a device port plus the hosting ability? I just don’t have any other part of my setup that can be a host outside of my Mac Mini and iPad.

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Prior to USB C, host/device was a physical thing, but USB continues to assume that one end of the cable is the boss of the other, and does the scheduling and the decision making. If you start plugging a modern Android device into random things (please don’t) it will sometimes just work and sometimes ask you whether it’s supposed to be the boss or not—before it can start transferring data.

Or we could say it’s the responsibility of the host to understand anything that might get plugged in, while the device just does whatever it does.

So I don’t think it’s “not right” to say that in the world of USB C “hosting ability” is a property a port might or might not have, and as I say my phone is physical proof of this, but I think it’s more useful to think of the host as the root of the tree (or local sub-tree), even when that “tree” is one wire, a single stalk. So in particular, if you use a hub, the hub plugs into the host and allows extra devices; the other way around is USB nonsense.

I think what my phone is doing is what they call “OTG” which, as I understand it, means that the endpoints check which side can provide the most power and makes it the host pro tem. You would think that this—or some refinement of it—would just be the norm nowadays, especially since IIRC FireWire got it right long ago—it simply makes the device with the highest serial number in the entire connected set the leader—but… no.

So, the underlying signalling technology nothwithstanding, the intended mental model is like (the consumer view of!) house wiring more than IP networking or MIDI chaining.

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it terms of midi communication - yes.

the main thing about a host is that it can provide power. i.e. a host can provide power to a device, not the other way around.

also, a device can only be connected to one host, whereas a host can connect to multiple devices e.g. usb hub,

note: Im talking here from a user perspective, as I think including more technical / development details would just cloud an already confusing (from a user side) topic :wink:

I will say, it’s true we are seeing more devices that have ports that are dual role,
i.e. the same port can be configured to either host OR device.
(some can detect and auto configure too) - from that perspective usb-c makes more sense.

unfortunately, it doesn’t make it less complicated for the user, as the role is still there.
it doesn’t magically turn the usb protocol into a peer to peer relationship :wink:

@SteveElbows - oh, Ive seen this many things…
usually it comes when people want to connect something to a computer e.g. to send midi from a daw… Ive seen this many times on eurorack modules (based on rPI often), but also the Organelle.
(lost count of the number of times Ive been asked about usb host to host adapters, or can they get a usb-a to usb-a cable ;))

also recently on the Eagan Matrix Micro Module (also the eurorack module), theres have usb device, when people would like to connect usb devices to them.

those are just ones I can think of off the top of my head… its pretty common.

as I said at the beginning, from a user perspective, in terms of USB MIDI (only) - the host / device distinction is a common source of confusion.

(again, Ive done a lot of usb device programming, axoloti, eigenharp, eurorack modules … so Im well aware of the technical / dev differences etc…but think its better to keep it simple, and not go too ‘deeply into the weeds’ :wink: )

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In terms of my specific situation, I connected my MIDI Device port on the Erae to my Meta Module’s USB port and it worked fine. Then I took the same cable and connected the MIDI Host port to the MM with same preset, careful to make sure the output of the Erae was set to the MIDI Host port in EraeLab for the Erae Keyboard layout (and careful to push the layout :)) and there was no response.

Not meaning to belabor the point any more, but wanted to spell out exactly what I did. Seems like it should work.

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yes, because the Meta Module is a usb host, so needs to be connected to the usb device port. (mm) host → (erae) device.
you cannot connect meta module host to erea host … host to host does not work in usb.

thats the issue with usb-c it makes people think is a peer to peer connection which it is not.

a good way to remember this is,
if you can connect a (simple) usb midi keyboard or a usb memory stick into a device - then its a HOST.
if you can connect it to a computer, then its a DEVICE.
(there are exceptions, but its a good rule of thumb)

even though, I know the difference, with something like the Meta Module which could theoretically be either (as usb-c)… I remember its a host, because I remember that you can plug a usb memory stick into it (as an alternative to the sdcard) :slight_smile:

thats kind of how I keep track of stuff, Ive not used in a while - without checking the manual/specs.

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Interesting and super helpful. Thank you! I wish there was a way for me to be connected to my computer to work on layouts while I’m sending MIDI to the MM. I tried all the routing options. They sound like they sould route the device to the host port but that didn’t work. Thanks for all your help. I hope this info will help anyone else who is unclear about all this!

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for now, use a usb → midi din adapter for MM. then connect via the erae TRS cable to midi din. bit clunky but works, and USB MIDI adapters are pretty cheap.

I’ve got a few solutions for these midi routing issues that Ive bought over the years :laughing:

that said, iirc, 4ms are going to release a mm expander that has a trs midi jack. so you could wait for that. we don’t have a date… as the audio IO expander is next on the list.

(honestly, I think they should have put a trs jack on the MM… a bit of a silly omission imo)

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I’ve had good success with the CME WIDI Jack, but I have the trs version. I’m kinda amazed it works so well. Though it so quickly pairs with any bluetooth nearby that I have to make sure bluetooth is off for every device except the one I was to use it with. I think I’ll wait for the expander!

Interestingly, sending Erae host out to Disting NT (which I confirmed is a MIDI device port) doesn’t work either. Sending it MIDI from Bitwig over USB does though.

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sorry, I don’t have a disting NT, so don’t know why you’d have issues with it.
probably something you’d have to discuss with Os.

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