Technical Info on USB MIDI - 7 Bit and 14 Bit

[BentoSan]

Great article - Im sure that is going to help a lot of people.

I think your statement about 14 bit midi & zero latency is a bit of the mark though.

Zero latency is absolutley not possible, and while the actual time period for 14 bits of data to be transferred at 10 Mb/s is 1.4 uS, both computer operating systems and USB are far from real time. When it comes to midi data latency is still in the order of milliseconds is the norm, regardles of if it is 7 or 14 bit.

Also a 14 bit midi message adds roughly 1 more ms of latency than a 7bit midi message, this is because there is one 7 bit midi message sent every 1 ms. In a 14 bit midi message 2x 7bit messages are sent, so thats where you get your extra 1ms of latency.

[DJ Van Draken]

Great article - Im sure that is going to help a lot of people.

I think your statement about 14 bit midi & zero latency is a bit of the mark though.

Zero latency is absolutley not possible, and while the actual time period for 14 bits of data to be transferred at 10 Mb/s is 1.4 uS, both computer operating systems and USB are far from real time. When it comes to midi data latency is still in the order of milliseconds is the norm, regardles of if it is 7 or 14 bit.

I'm glad you added this, midifidler. I was only describing the difference in USB and MIDI cables as far as protocols and wiring is concerned. Overall system speed and processing is ENTIRELY separate, as this depends on the software and the hardware being used. So yes, my numbers are only estimating the time it takes to go from USB output to USB Input... Nothing else is included. It would be too complex to calculate for everyone; sorry for any confusion.

[DJ Van Draken]

As far as A/D conversion and MIDI bit-lengths are concerned, this is going beyond the scope of my blog post, since I will admit that I don't know enough about the subject to post. You COULD have an analog input that sends an analog signal to a separate A/D converter... but many modern devices simply sample your analog input on the control itself... much like your camcorder samples real life at 30 frames per second (i.e. 30 pictures a second).

Your analog control input can be converted into a digital output by an encoder... I've seen them with up to around 20 bits or so. The encoder takes the data and sends it to the MIDI microchip processor, which must be capable of handling at least 14 bit messages. The messages are queued alongside the other controls midi messages and sent down the USB line. The time it takes for the actual USB interface to send and receive data is very quick. The time for the data to be separated and processed is another story.

[DJ Van Draken]

BTW thanks for all the reads and comments guys.

[midifidler]

Its allways hard when writing an article like this to walk the line between a simplified technical explanation and to much information!

Well done!