USB MIDI interface for the NeXTCube – ISPW board

https://0110.be/posts/USB_MIDI_interface_for_the_NeXTCube_-_ISPW_board

by zdw • 3 years ago

65 7 3 years ago

dfox• 3 years ago

One thing that this article mentions is that MIDI is a interface that is inherently optically coupled. The notionally differential wires end up in the LED inside of an optocoupler. Reason for that design is a general aversion of audio people to anything that might cause what they call “ground loop”.

And then well, in 21st century there are various half-assed implementations of the MIDI physical layer (mostly assuming that it is essentially a TTL) that end up non-working and non-working because of the ridiculous currents that flow through the cable that shorts ground of one device to the power bus of another.

pantulis• 3 years ago

I swear I have _heard_ sysex dumps on my speakers, specially using older serial "To-Host" cables.

boffinAudio• 3 years ago

You have to try pretty hard to mess up MIDI, hardware-interface wise. Its one of the most widely understood and implemented serial protocols out there ..

jalk• 3 years ago

Here is a snip from the midi specification

The MIDI circuit is a 5mA current loop; logical 0 is current ON.... To avoid ground loops, and subsequent data errors, the transmitter circuitry and receiver circuitry are internally separated by an opto-isolator

Ground loops is not something the audiophools have cooked up. Ethernet devices are also isolated from each other, although it uses 1:1 transformers (Ethernet Magnetics) instead of optocouplers.

The optocoupler also works like a cheap (although somewhat hard to replace) fuse which is probably a good thing if you want to connect you Roland Jupiter-8 / Fairlight CMI to some dodgy equipment.

zdw• 3 years ago

Ethernet devices are also isolated from each other, although it uses 1:1 transformers (Ethernet Magnetics) instead of optocouplers.

Unless you're using fiber as your medium, but that's an optocoupler by definition...

grawlinson• 3 years ago

The optocoupler also works like a cheap (although somewhat hard to replace) fuse which is probably a good thing if you want to connect you Roland Jupiter-8 / Fairlight CMI to some dodgy equipment.

In this case, the older synths are more likely to have failing/dodgy components. I have a DX-7 that I'm going to have to replace a lot of components in, and this sort of knowledge/understanding really should be more common along synth enthusiasts.

datpiff• 3 years ago

Roland Jupiter-8 / Fairlight CMI

Funnily enough neither supported MIDI. The CMI Series IIx got it as an upgrade, the Jupiter-8 only supports it with 3rd party modifications.

USB MIDI interface for the NeXTCube – ISPW board

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