chatterbox Posted December 26, 2009 Share Posted December 26, 2009 I have 2 x edirol usb 101 boxes. The plan is to run computer A off box 1 and computer B off box 2. The Show would be running on one computer with the second ready to go if there is a problem. I send midi info out of the edirol to a reverb unit... I want to hard wire the 2 midi sends out of the 2 edirols into the one midi in on the reverb.. bearing in mind that at no time would the midi info have to be merged , as only one computer will be running at any one time.... do I need a midi merge box? or can I just join the 2 midi cables at the end to go into the reverb...?? AS a side issue.. same set up - the 8 audio outs on the 2 edirol boxes will also be hard wired in the rack so that output 1 for box 1 and output 1 from Box 2 will go to the same socket on a back panel on the rack box - ( the loom from the mixer inputs would be plugged into this)...... again as a backup, so that only 8 channels need to be used on the mixer - now I believe that although only one computer wil be running at any one time - I will need to have a switch to turn the sends from one edirol box off - as otherwise some signal lose will result as the signal from the working edirol will not only be sent to the socket and onto the mixer, but will also be sent down the cable to the other edirol???? Is this correct? As weight in the rack is a BIG issue (has to fly as hand luggage) is there another way of doing this and not using switches, or can one switch be used to control all the 8 audio lines from the edirol instead of 8 seperate switches??Maybe a DPDT switch would do it??? does this all make sense?? Any help, suggestions etc would be appreciated... Thanks Link to comment Share on other sites More sharing options...
paulears Posted December 26, 2009 Share Posted December 26, 2009 You 100% cannot join two midi feeds into one - to do this you must use a merge - although the problems with timing when using merge boxes shouldn't matter if only one of the computers is feed active data. I'm assuming you're using the audio interface midi outs to control the reverb parameter on the reverb unit? If this is all it's doing, then it might be worth checking that the Edirol interface doesn't have an a facility for making the out a thru as well - if it does, then assuming (and you'd need to check) that the thru is active even if the connection to the computer goes down, then the output from one could go to the other, and then the merge wouldn't be needed. If you already have the Edirols, then it's worth checking. Link to comment Share on other sites More sharing options...
TomHoward Posted December 26, 2009 Share Posted December 26, 2009 To switch all eight audio sends (and the MIDI) you could use one SPDT switch to switch a load of relays, rather than using a multi-pole switch. Link to comment Share on other sites More sharing options...
sleah Posted December 26, 2009 Share Posted December 26, 2009 To switch all eight audio sends (and the MIDI) you could use one SPDT switch to switch a load of relays, rather than using a multi-pole switch. In a similar way, why not just mechanically switch the midi lines too? Link to comment Share on other sites More sharing options...
Rob_Beech Posted December 26, 2009 Share Posted December 26, 2009 The idea here is that the switch won't be automatic. So there will be some down time from the outputted signal. As this appears to be the case, manual switching and sync isn't going to be critical, as long as it's as close as you can get it manually. If the audio disappears for a couple of seconds when you make the switch, if its 100ms out of sync with the original (failed) source when you get it back live then nobody will notice, and if they do, congratulate them. you DO need switching, or something other than a passive combine on both the midi AND the audio. A set of resistors may help on the audio side but merging the midi is the only way to do that side (unless you manually unplug and replug the other in. Of course, remember that depending on teh interface, plugging in a midi cable can send a rogue signal one way or the other so be aware of potential issues like this. Rob Link to comment Share on other sites More sharing options...
Brian Posted December 26, 2009 Share Posted December 26, 2009 If you can guarantee that only one MIDI transmitter will ever be sending then you can combine MIDI with just four diodes (usually). MIDI works by sending +5V on pin 4 of the output DIN connector out to the receiver, which is just an optocoupler, with the current flowing back into pin 5 which connects to a current sink (usually an open-collector device). If you were to combine the +5v signals with two diodes with their cathodes commoned and fed to the receiver, and combine the sinks with two diodes with their anodes commoned and fed from the receiver then with a following wind it'll work. You'll need to use low voltage drop diodes. It'll fail if the inactive transmitter send any sort of message which might be happening in the background. Link to comment Share on other sites More sharing options...
mackerr Posted December 26, 2009 Share Posted December 26, 2009 It seems kind of silly to have all that back up available and not run it as a live back up. It is straight forward to build a single toggle switch that can switch all 8 channels of audio and the midi. This would let you throw one switch to put your entire back up system on line. The brand of switches I am most familiar with for this application is the T-Bar 902 series. These are available up to 144 pole double throw in multiples of 12 poles. You only need a 24PDT. Build a 1RU rack box with multipin for your console, each edirol, and each midi, and it will weigh less than a few pounds. The advantage of the toggle switch vs relays is that the switch does not require power, and will be lighter, and perhaps cheaper although these are expensive switches. Mac Link to comment Share on other sites More sharing options...
paulears Posted December 26, 2009 Share Posted December 26, 2009 Brian - what happens to the midi clock pulses? Merging like this would result in double sync and wouldn't that ###### things up? Even if you found a way to disable output from one midi transmitter, you'd then have to re-enable it to be able to use it? Link to comment Share on other sites More sharing options...
Brian Posted December 26, 2009 Share Posted December 26, 2009 Brian - what happens to the midi clock pulses? Merging like this would result in double sync and wouldn't that ###### things up? Even if you found a way to disable output from one midi transmitter, you'd then have to re-enable it to be able to use it?They would indeed mess things up. The MIDI spec does not call for the constant transmission of MIDI clock/sync words; it's a function of the driving software. Perhaps the OP can clarify what software he is running and what he really means by......running on one computer with the second ready to go if there is a problem...as only one computer will be running at any one time Link to comment Share on other sites More sharing options...
Russ83 Posted December 26, 2009 Share Posted December 26, 2009 I'm not 100% sure if this would work but it is something I would try.If you are good with a soldering iron then buy one of these 25 pin printer switches and a few ends to make up some breakout cables (or buy normal 25-way D-Type cables, cut in half, strip and use crimps onto your existing cables to make your breakout cable). The switch is fully mechanical and is supposed to have full 1-1 connections so I don't see why it wouldn't work for both your MIDI and audio. I'm not saying buy from Maplin but that was the first one to come up! Alternative from our usual friends: SWITCH Link to comment Share on other sites More sharing options...
cedd Posted December 26, 2009 Share Posted December 26, 2009 Russ's idea may indeed be the cheapest way of doing this. However it's worth checking that the switch does indeed switch all 25 pins over. In practice I've never seen more than 3 pins on an rs232 port be used (TX, RX, GND) and so the switch may not change all 25 over. There will always be a single point of failure in a system like this, I know sound engineers who carry 2 PC's "just in case", then lost the mixing desk power supply and lost the entire show anyway! The question is mitigating the most likely risks. Is a PC failure going to be more likely than a failure of your switching arrangement? If it's a mechanical switch, then probably not (assuming your soldering is ok!). Relays too are pretty reliable, the power supply is probably more likely to fail. PC failures are no doubt some of the most likely things to go wrong. That said, I have never seen a single tasking (audio playback only), non-internet access pc, without antivirus (on a "clean pc" it's far quicker without), fail in operation. That goes for theatre, and my day job in Air Traffic Control. Clearly hardware failures (power supply) are different, but I've purposefully left them out as they're just as likely to happen on a pc as an amplifier, or a mixing desk. You can't mitigate for everything. You could do your audio combination using transformers, however with any combined signal, be it midi or audio, complete failure of one side is one thing, corruption is a different thing. Imagine if your midi port starts spitting out random garbage, or program changes, or whatever. A mege situation means that data still gets through.Likewise with audio, if a track gets stuck and the computer freezes, you're now going to end up with the changeover audio, plus the skipping track, or looping cue that refuses to stop or whatever. Link to comment Share on other sites More sharing options...
chatterbox Posted December 27, 2009 Author Share Posted December 27, 2009 Thanks for all the answers so far... to answer the questions raised in the replies... we run scs software - we have 2 computers and 2 edirols set up and 1 reverb fed from midi. We only have one computer running at any one point... if it fails then there would be a glitch, but the show would finish the current song, and then I would kick in the back up computer etc...Therefore there would be no midi info coming out of the unused computer to worry about regarding the merge.. The 2u rack we are putting together would contain the reverb (TC M350 - 1ru) and the 2 x 1/2 rack edirols....there will be an aluminium back plate with the sockets etc on for the audio to plug the mixer loom into.... weight is the major problem - the whole finished rack HAS to come in at 7kgs max to carry on as hand luggage ( we fly alot) the total of the 3 units is 3.9kgs - we are constructing a lightweight rack with corflute and aluminium extrusion - the back plate and sockets etc need to be as light as possible....we could use a midi merge box, but that would add weight - that is why we are looking for an alternative... we would hardwire 2 small looms with jacks out of both 8 audio sockets on the back of the edirols and "merge" them into the back of the 8 sockets on the back panel for the mixer to plug into.... Once we have sorted the patching problems and built the case - we will see what weight allowance (if any) we have left - it may be that the psu's etc will have to be carried seperately and plugged in at the venues... Link to comment Share on other sites More sharing options...
TimmyP1955 Posted December 27, 2009 Share Posted December 27, 2009 On the audio question: Sum the outputs - http://www.rane.com/note109.html or Get a box - http://www.radialeng.com/re-sw8.htm Link to comment Share on other sites More sharing options...
paulears Posted December 27, 2009 Share Posted December 27, 2009 Just a thought, but is the midi conrol of the reverb essential - in an emergency could you switch progammes from the front panel instead. Multipole switches do work in examples like this. BR member grum has multi universe DMX switch for fast changeover at festivals, that kind of thing. I think its 8 ins x 2, with one 8 out - so he can switch from festival control, to his control without repatching live. Apart from the soldering, making up this kind of thing for your audio and midi would seem the simplest way to do it. Link to comment Share on other sites More sharing options...
sleah Posted December 27, 2009 Share Posted December 27, 2009 Imagine if your midi port starts spitting out random garbage, or program changes, or whatever. A mege situation means that data still gets through.Likewise with audio, if a track gets stuck and the computer freezes, you're now going to end up with the changeover audio, plus the skipping track, or looping cue that refuses to stop or whatever. Which is exactly why any kind of merge solution will not help and may make matters worse :) Audio software freezing has a nasty habbit of sending out a loop of a couple of frames of audio - not a nice noise! You will end up doing the 'hold-the-button-in-for-10-seconds' to power off in which case you could have physically swapped the plugs around...... To draw on a parallel example, the community FM radio station I help out at has a mechanical switch to switch over to the back-up studio :) Link to comment Share on other sites More sharing options...
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