[sdiy] MIDI Clock sync advice

brianw brianw at audiobanshee.com
Sat Mar 9 23:31:24 CET 2024


On Mar 9, 2024, at 8:47 AM, Benjamin Tremblay wrote:
> Let’s pass usb midi through TOSLINK and call it a day.

Don't say that! ;-)

USB-MIDI is not MIDI. *

Better to say, "Let's pass Classic MIDI through TOSLINK and call it a day."

Ideally, "Let's pass MIDI over ethernet and call it RTP-MIDI." ... and wha'd'ya know, we already have that! Ethernet is generally ground isolated, although it's best to design for even better isolation than is typical.

FireWire is another existing standard for MIDI transport, although FireWire is now dead.

If you think about all of the other standards that have come and gone, it's incredibly impressive that MIDI has lasted 40 years, and modern gear can still connect to original gear. There aren't many standards where electronic devices from 40 years ago will work with modern equipment without some adapter.

Brian

(*) USB-MIDI converts MIDI messages that are 1 to 3 bytes long into 4-byte packets, where the added 4th non-MIDI byte includes redundant type information that can unfortunately be inconsistent with the same type information in the Classic MIDI message. Yes, I've seen actual USB-MIDI implementations where the two types conflict with each other, and there's no way to know which type is correct and which is in error. USB-MIDI also delays MIDI information by up to 1 ms in the best cases (0.5 ms average), even more when the USB Host has scheduling issues, and transmits the information without any time stamp that might indicate the timing of the original MIDI message before the USB framing delay. Because of all of the changes that USB-MIDI introduces, it would be best not to duplicate those for non-USB transports like a hypothetical TOSLINK transport. Instead, it would be better to follow the precedents set by other alternative MIDI transports that the MMA has specified.


> On Mar 9, 2024, at 11:05 AM, Mike Bryant wrote:
>> Nothing is stopping equipment having USB ground isolation - it's just never specified.
>> 
>> From: John Speth
>> Sent: 09 March 2024 15:14
>>  
>> On 3/9/2024 7:00 AM, Benjamin Tremblay via Synth-diy wrote:
>> > USB is just not ideal for music devices because of the star networking pattern. If we could evolve to a point where every usb cable is usb C and all connections are peer-to-peer, we could finally sunset five pin midi.
>> 
>> Except that 5 pin MIDI has the most excellent ground isolation. We don't 
>> get that with USB MIDI.




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