On Friday 25 December 2015 09:04:22 Ralf Mardorf wrote: > On Fri, 25 Dec 2015 13:38:01 +0100, Yves Guillemot wrote: > >Le jeudi 24 décembre 2015, 11:48:07 Bob van der Poel a écrit : > >> I believe that the MIDI spec > >> > >> http://www.midi.org/techspecs/electrispec.php > >> > >> says that you must have a opto-isolator. Devices without one are > >> probably not compliment ... don't know about direct usb > >> connections. > > > >MIDI uses an unipolar signaling which is very sensitive to > >electromagnetic noises, in particular those ground loop generates. > >That's why MIDI standard requires an opto-coupler. > > > >USB uses a differential signaling and can works without any galvanic > >isolation. > > Signal routes could be very tricky. A keyboard could be directly > connected by MIDI to the PC, but audio of the synth might be connected > to other gear and this gear is connected by audio to the PC. Galvanic > isolation and an open shielding always could make a difference. > There's also to keep in mind, that connections could be done by USB to > MIDI DIN adapters. > > In the last 35 years music equipment became much cheaper, electronic > components became much better, but design of circuits and/or > carefulness of soldering and assembling became very worse. ISO 9000 is > just crap to provide good-for-nothing idiots a quality management > manager job to reduce quality, before that hype the quality of > circuit design and carefulness of soldering and assembling was much > better. > > 2 Cents, > Ral Ralf et all; Having on several occasions, dealt with venues that were wired by color blind electricians, I look at galvanic isolation as a hard and fast rule where it can be done. Musicians with their own gear, routinely flip the polarity of ground switch on the front of the amp for least hum. And just as routinely break the 3rd pin off their power plugs because the venue is too damned old to have ever had a static ground in the duplexes anyway. Or if that worn out duplex has been replaced by a stage hand who never saw a copy of the NEC, the 3rd pin may not be connected to anything but the handybox its in. And too many times that has led to the whole stage lashup being hot enough to kill if a real ground is contacted. "portable" venues constructed on site by the usual group of "roadies" should be tested by a qualified test person and confirmed each time they are assembled, with the results posted where the talent can read it as they enter. Having opto-based galvanic isolation in the midi spec should not be skipped just because its USB with its differential signalling and doesn't stop working when theres a 3 volt+ AC potential to ground. The fact that this AC potential is even present, should be grounds that you write it into the performance contract that if his gear is defective, he can't use it on your stage. By that same contract, the smarter musicians who do know about such things can refuse to perform if the venues wiring isn't up to code. And he should still be paid in that event, as its not his fault. The quietest studio/control room lashup that ran on 60 hz power I've ever not heard, is actually powered by a big (5kw rated) 250 volt center tapped transformer, powered by the 127 line applied across the 250 volt terminals, with the secondary's center tap on its own deep earthen ground so the secondary's 1/1 line voltage from pin to pin was still 127, but it was a balanced 63.5 volt to ground on each pin. The equipment plugged in didn't know it was specially powered, but the board, which had single ended inputs, had a hum level that was about 90 db down from a live microphone input. Thats as close to never mind as you can get even with true differential inputs, and was about 2 grand lower in cost to build. Biggest problem? Convincing the electrician who installed the transformer, that it actually met code. It may not in some locales that write their own version of the NEC. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
