If a multimeter shows zero resistance between the metal shell of the plugs at each end of a MIDI cable, discard it.ĪES/EBU normally uses balanced connections with transformer isolation (signal 'pulse' transformers are used, which are the tiny black boxes you can often see on soundcards near their digital I/O sockets). Avoid five‑pin DIN hi‑fi cables and use proper MIDI cables, which use only pins four and five for data transfer, and connect the cable screen to pin two only at each end of the cable, but not to the metal shell of the plugs themselves. A few MIDI In ports (mostly on budget PC joystick/MIDI adaptors) may omit this circuitry, to save a few pennies, but the most common cause of MIDI ground loops is using an incorrectly wired cable. MIDI inputs also incorporate opto‑isolators, so plugging in a MIDI cable should never result in a ground loop. Let's look at the easiest options first.ĪDAT and S/PDIF optical both use fibre‑optic cables, giving true galvanic isolation, just like a transformer, so they can never result in ground loops. Here's a quick run‑down of possible problems you might experience, plus some ways to avoid them. However, if a digital audio connection completes a ground loop, it may indeed result in characteristic hums, digital whistles and whines appearing in your analogue audio signals. The tiny ground‑loop signals are rarely sufficient to result in corruption of the digital data itself, since that either gets through or it doesn't. Unfortunately, in practice such problems do occasionally occur, either due to incorrectly wired cables or to shortcuts taken by the manufacturer of the gear in question. SOS columnist Martin Walker replies: In theory, most digital connection formats incorporate safeguards to prevent ground loops. Their metalwork is insulated from the PCI backplate, and the small black component immediately above them on the circuit board is the pulse transformer for the output, which prevents ground loops. M-Audio's Audiophile 192 is an example of a soundcard with well‑designed S/PDIF sockets. Is the same true of digital audio cables? In SOS December 2008, you explained how USB and Firewire cables could complete ground loops and result in audio problems.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |