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MIDI cable length versus reliability and latency

“We have a MTP AV USB and the question of MIDI cable length and latency has come up. What are the length / latency specs for MIDI cables? We understand the use of quality cable and have seen product from Monster cable in lengths of 50 ft., Pro C0 in 30 ft., and HOSA in 25 ft. We have been told that 20 feet is the maximum cable length before latency will be a problem. We are using a 2408 MK II w/ Digital Performer, a Mac G3 B/W, 450MHZ, 896 MB Ram, Adaptec 39160 card, (2) Seagate drives and understand there will be some degree of accumulative latency within the system as a whole. This system is in the setup stage so actuals are unknown. Any guidance / direction would be appreciated.”

(For the record, the person who sent in this question is a Sweetwater customer. The e-mail was forwarded to Tech Support who has already responded in detail. But we still thought this would be an interesting question for inSync.)

It appears that you may be confusing audio recording issues with MIDI issues here. Latency is generally not much of a problem with MIDI data, but can be an enormous problem in audio recording. Your choice of MIDI cable will have no effect on the performance of your audio recording system. The biggest factor for latency in your system is going to be the performance of your CPU.

Though there are a few who will quibble with this statement, your inSync editor says that MIDI cable length does not contribute noticeably to MIDI latency. Or, at least no one has been able to prove it does. MIDI cable length does, however, affect the quality of the MIDI signal, and in that way can have a bottom line effect on the reliability of your MIDI system. These reliability problems can manifest themselves in ways that may appear to be latency, but are not. MIDI is an unbalanced audio signal so cable length and quality has the same implications as unbalanced audio lines: shorter and higher quality are better. 20 feet is a very safe and conservative limit for MIDI cable length. Runs of 50 feet or more are possible with high quality cable. If you are having reliability problems (dropped or stuck notes, things falling out of sync, erratic controller operation) you need to check your cables, and their environment. Environment in this context means to look at what your cables are near. If they are running next to sources of interference they may not work as reliably. Treat MIDI cables no different than audio cables.

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