djimbe Posted September 9, 2008 Share Posted September 9, 2008 Hiya. I'm trying to verify what I need to do, and in the way of eq, to get the mix from my Macbook Pro to a PA system, or perhaps a mix desk. The Macbook is running music software. The output is already mixed by midi controllers before it leaves the computer. The computer is connected to an external USB audio interface which outputs as a stereo pair of balanced 1/4". What I remain unsure about is the need for a DI box. Ultimately I want to connect to whatever system the club/venue is using. Is this always going to be XLR? Or might it be a mixing desk with 1/4" ins? If it does use 1/4" ins, would I still need a DI box between the audio interface and the desk? Do I need to go through a DI box after the audio interface 100% of the time? Just vague in general about the DI box and also how it works re: balanced outputs. Cheers Link to comment Share on other sites More sharing options...
Bobbsy Posted September 9, 2008 Share Posted September 9, 2008 If your external sound card is a balanced output as you say, you shouldn't need a DI box. The main thing a DI does is take an unbalanced source and balance it prior to sending it down a cable to the mixer--and your source is already balanced. As for the connectors in use, you will likely encounter both XLR and 1/4 inch TRS. Carrying simple (and inexpensive) adaptor cables should be all you need to deal with this. The other thing that might be useful is an adaptor or cable that lets you lift the signal earths should you encounter a problem with hum in some locations. Hope this helps. Bob Link to comment Share on other sites More sharing options...
djimbe Posted September 9, 2008 Author Share Posted September 9, 2008 Cool, thanks for the clarifications. The other thing that might be useful is an adaptor or cable that lets you lift the signal earths should you encounter a problem with hum in some locations. Ah right. Is the implication that there could be hum if the PA/mix desk is unbalanced? Though XLR is balanced by definition. But I suppose a mix desk could be unbalanced. Link to comment Share on other sites More sharing options...
Jivemaster Posted September 9, 2008 Share Posted September 9, 2008 While DI boxes are usually used to connect an unbalanced source to a balanced line and may likely match impedences too, There is sometimes a need to isolate the source and the output of your situation from each other to prevent ground loops and excessivs noise ( usually caused by the lappy psu's earthing ) Ownership of a a stereo isolating unit or matching transformer with the sorrect connections may help in some situations. Consider carefully the grounding arrangements. noise from the smpsu feeding the lapptop can aflict qualty badly. Link to comment Share on other sites More sharing options...
Ben Langfeld Posted September 9, 2008 Share Posted September 9, 2008 Consider carefully the grounding arrangements. noise from the smpsu feeding the lapptop can aflict qualty badly. But with it being a Mac, you won't encounter these problems Link to comment Share on other sites More sharing options...
berry120 Posted September 9, 2008 Share Posted September 9, 2008 But with it being a Mac, you won't encounter these problemsNot necessarily the case, the external sound card might have a seperate power supply... As long as there's enough DI boxes to go round (not usually a problem) I tend to DI everything with a 1/4" output by default, a) because it's not going to hurt, b) because it converts the plug type to XLR so I don't have to search through an adaptor box, and c) because most of the time it is actually necessary, and d) even when there's balanced outs it helps with grounding issues like Jivemaster said. Word of caution though if choosing a DI box, the Behringer DI20 is one to stay away from... It might come in at an attractive price point and handle two channels, but it's 'orrible. The Behringer DI100's are fine, studiospares make one of their own which has been fine for me, but that DI20 is definitely not! Link to comment Share on other sites More sharing options...
djimbe Posted September 9, 2008 Author Share Posted September 9, 2008 But with it being a Mac, you won't encounter these problemsNot necessarily the case, the external sound card might have a seperate power supply... The Macbook Pro's headphone jack is quite noisy if you listen through it directly. I read this may be related to it physically doubling as an audio optical out. But this doesn't matter for me now 'cos the audio is coming out of the audio interface. I'm using a Behringer FCA202, which can make use of an external supply. I generally do use that supply to take some load off the computer. Btw this has been an extremely good device. Very compact and good sound quality. I haven't experienced any hum, interference or noise thus far while running my rig to various amps via the Behringer. But I've never tried it out with some big, unknown PA yet either. So it sounds like I should probably head towards getting a DI box, then. Link to comment Share on other sites More sharing options...
King_Tom Posted September 9, 2008 Share Posted September 9, 2008 Yeah, I'd definately DI, I do quite a bit of live sound, especially with DJ's (Ableton boys on laptops) and as a rule of thumb we always DI the DJ's, maybe not always needed, but I'd rather do than not. I use a couple of LA audio Di2 boxes, lovely sound, and all the usual features. They do a new one now with RCA inputs on it as well (I think) which sounds like it might be right up your street. Tom Link to comment Share on other sites More sharing options...
berry120 Posted September 9, 2008 Share Posted September 9, 2008 The Macbook Pro's headphone jack is quite noisy if you listen through it directly. I read this may be related to it physically doubling as an audio optical out. But this doesn't matter for me now 'cos the audio is coming out of the audio interface.Most headphone jacks built in are quite noisy, mac or no mac - I'd never use one direct to a PA unless there really was no other choice! I haven't experienced any hum, interference or noise thus far while running my rig to various amps via the Behringer. But I've never tried it out with some big, unknown PA yet either. So it sounds like I should probably head towards getting a DI box, then.I'm not saying running it through a big, unknown PA system will suddenly cause hums where they weren't before, just that if you DI it that should minimise the risk of problems occuring. So it sounds like I should probably head towards getting a DI box, then.Without wishing to state the obvious, you'll need 2 Link to comment Share on other sites More sharing options...
mervaka Posted September 9, 2008 Share Posted September 9, 2008 .. unless he gets a stereo! seriously though, people should make phantom powered DI boxes with DACs and a usb jack on the end for this sort of thing. basically a phantom powered sound card. Link to comment Share on other sites More sharing options...
djimbe Posted September 10, 2008 Author Share Posted September 10, 2008 Thanks for all the advice so far. I'm starting to look 'round for a good stereo DI box to buy here in Sydney. Link to comment Share on other sites More sharing options...
Jivemaster Posted September 10, 2008 Share Posted September 10, 2008 If the kit is yours from laptop to speakers then you can try without an isolating transformer. If you will be plugging into other people's PA then isolation and signal ground lift could be a necessity at any gig so carry one and know how to use it. Link to comment Share on other sites More sharing options...
berry120 Posted September 10, 2008 Share Posted September 10, 2008 .. unless he gets a stereo!Oh yeah... IIRC Samson do one that seemed ok last time I used it, you might want to look in that direction. Link to comment Share on other sites More sharing options...
djimbe Posted September 10, 2008 Author Share Posted September 10, 2008 Oh yeah... IIRC Samson do one that seemed ok last time I used it, you might want to look in that direction. Ah, I'm glad to hear you say that! My searching at first was turning up only Behringer. They seem to have a real stranglehold on audio hardware distribution in Australia. Anyway, harder googling uncovered Samsons's stereo DI box, before I saw your post, and I am already a fan of Samson's. I have now found one dealer here selling these here, in Victoria. Link to comment Share on other sites More sharing options...
Solstace Posted September 10, 2008 Share Posted September 10, 2008 ...phantom powered DI boxes with DACs and a usb jack on the end for this sort of thing. basically a phantom powered sound card. [rant]Honestly I can't think of anything less desirable right now... "But my laptop runs Linux""It says it needs a driver, but I don't have an admin password""Well it's never crashed until we plugged it into YOUR system!" Nope - When I'm on noise, the last thing I need is to be providing IT support. Give me a line-level output or give me nothing at all.[/Rant] Link to comment Share on other sites More sharing options...
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