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I want to mirror the data sent to (and/or from) a USB device to multiple host computers at the same time (i.e no physical switches to select one host or the other). Here are two scenarios to describe what I'm trying to do from a device's perspective:

  • Send Data: A USB microphone is hooked up to two computers such that when spoken into, the mic level on both computers increases simultaneously
  • Receive Data: An audio signal from each computer is transmitted over USB and "merged" before entering a DAC for external processing, effectively combining each computer's audio signal

My (limited) understanding of the USB protocol and other similar posts on StackExchange (1, 2, 3, 4) tell me that this isn't really possible, however, during my research on this topic I stumbled on these videos:

These seem to demonstrate that what I'm trying to do is possible, at least for sending data from the device. Can USB data really be mirrored in this fashion if it's done via RS232 connections? I've found the product page here, however I'm still skeptical of this and would like to see other examples of similar devices. Does anyone know what the generic name for a device like this is/know of any other examples of devices like this?

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The device described in the video is perhaps similar to the USB Barcode Scanner Splitter (UBS-120P), however it doesn't help with your problem.

This works for RS232 sources, but you can't split USB signals like this. USB is a Serial communication device that employs a USB (Communications) protocol.

USB uses two way digital communication where the device talks to the computer to tell it how it can send its data to the computer. The computer and the device perform a handshake where they agree on the format of the data that the device will be sending.

You can't connect the same USB device to two computers at the same time, because the device cannot do a handshake with two computers. The most you can do is broadcast the audio to be picked by other computers via the network.

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  • This is what I figured the answer was, however if that's the case, then how come the device in the video works? The barcode scanner shown isn't a RS232 source natively, rather it's a USB device which is converted to RS232 via the product featured. To put it another way: what is the difference between the barcode scanner and say a microphone that would allow the barcode scanner to work with this device but not the microphone?
    – user1251367
    Dec 14, 2020 at 20:39
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    The only possible way is if its firmware emulates two microphones and takes care of the handshake with both computers, then sends the barcode data to both. This is why this device is sitting in a box rather than being a simple splitter with two wires. I don't think such a device exists for microphones, or at least didn't find one on Amazon.
    – harrymc
    Dec 14, 2020 at 20:48
  • Workarounds: one mike to multiple PC's - have first PC relay signal to second, e.g. UDP broadcast, or use audio splitter. Two PC's to one DAC - 3.5 mm audio (or two bluetooth connections) to an audio mixer.
    – DrMoishe Pippik
    Dec 14, 2020 at 21:44
  • harrymc - Makes sense this would be at a firmware level, probably register it as a generic HID device since it can also work with a keyboard according to the product page, which likely wouldn't work with something like a mic. DrMoishe Pippik - I've though of similar workarounds, will probably do a network relay for the mic example. For the many PCs to speakers example, another workaround could actually be each PC having its own DAC, then using splitters to merge the analog RCA signals coming out of the two DACs before they merge go into a single amp, need to think about it more. Thanks!
    – user1251367
    Dec 14, 2020 at 22:18
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Those USB splitters are device specific. They work by decoding the input from a USB HID (human interface device) devices, splitting it out, and emulating duplicate HID devices to the connected computers. They will not work for anything other than USB HID devices. If you are wanting to mix and split audio signals then it would be far easier to do this with the audio than with the USB devices. If the goal is to maintain signal quality by keeping this digital as long as possible in the data path then doing so anywhere other than the USB part of the path would be far easier.

The use of RS-232 connectors on the devices you linked to has nothing to do with how the input signal is duplicated. The way they are using RS-232 is non-standard and is a good way to ruin hardware if someone wasn't very careful in using those cables.

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