Hello,

I need advice for an external soundcard to use with MacBook that will be feed to the PA. Only one track is out of the Mac, but there could be 2 Mac running. Is there any card that can connect 2 machines and feed them separately to the PA? Does the Apogee Ensemble can do this ?

Thank you.

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http://soundcloud.com/orgasmo-sonore Revisiting Obscure Film Music

A sound card can't be shared between two computers.

You probably don't need a sound card for what you are trying to do at all, unless your software doesn't work well with Apple's built-in audio.

You just need to adjust the level, balance and possibly mix the headphone stereo output to mono and feed it into a normal microphone XLR.

The built-in audio quality on most modern macs is quite good and I've never encountered a noise problem if proper isolation transformers are used.

If I need stereo, I sometimes just use a regular dual instrument DI (or two mono ones) because there are always DIs around.

Connect the Macintosh to the instrument inputs of the DIs with a Y cable that has a TS plug for each channel on one end and a 3.5mm trs cable on the other. These are standard cables, easily available. If you just can't find one, try a 3.5mm stereo to rca cable of the sort used to connect ipods to hifi systems with a pair of RCA to TS adapters.

If Mono is good enough, you can use just one DI and leave the other dangling. You can get mono output from the Macintosh by setting the "System Preferences / Accessibility / Play Stereo Audio as Mono "option which will mix the two channels and send them to both right and left outputs at the same time.

Don't be tempted to just use a Y cable to connect the outputs together this will cause distortion or even damage the output device (although a "passive mixer cable" with isolating resistors can be used if you have one).

Of course if the computers are close to the mixer you can skip the DI and XLR cabling and just plug the TS connectors right into line inputs on your mixer.


If you do need XLRs, The most convenient solution is something like this:

http://www.rapcohorizon.com/p-377-ltiblox.aspx

which mixes the left and right channels down to mono and sends them through a transformer to an XLR after allowing you to adjust the level with a handy knob.

I regularly use the Rapco devices to connect various things including MacBooks on stage here in the US because they are a complete solution and easily available, but similar things are made by many suppliers in both mono and stereo versions. Mono is usually a better choice than stereo for this kind of thing and it only ties up one XLR input.

If properly isolated, the Macbook's audio is quite flat and clean with low distortion. It has a very gradual and very slight roll-off below 100hz and above 15khz - but that's usually what you want anyway.

hope this helps,

M

Edited by mpvano (27/11/12 06:14 AM)

Hi Mpvano,

Thank you for your very detailed information. I'm just not convince by the fact that I "don't" need a soundcard, just for the complexity of your connectivity scenario.
Maybe the Apogee Ensemble is overkil, but if I use just the simple Apogee Duet for example, would it be better than y-cable/adaptor/DI/XLR configuration you suggest, replaced by a nice Apogee converter + 2 balanced XLR out with much less headache and better sound quality at the end (even if, I admit, the built in mac soundcard is very good)?

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http://soundcloud.com/orgasmo-sonore Revisiting Obscure Film Music

I'm not trying to be a Macintosh activist here - I'm speaking as an FOH sound guy who hooks up guys like you who show up with their computers and trying to tell you what works well for other people doing what you do.

In fact - I was doing exactly what you asked for on a video projection job this past week end.

The problem you face in connecting your personal computers is unlikely to be the quality of the sound cards you use (whether built in or outboard) - it's isolating them from the PA system to avoid ground loops and noise from stage lighting and the laptop's switching power supply and and getting the connectors and levels to match those needed by the cabling on the stage - if that's where you're putting them.

If that's NOT where you're locating your two computers - if you are putting them alongside the mixer in the control booth, then there's nothing special about the connection and you can use almost any interface you like as long as you have matching cabling. In many cases however, you'll still need some sort of isolation box to keep noise from the laptop power supply out of the mixer.

Even with expensive interfaces in recording studios, you still may need isolation equipment to keep noise from your computer out of the monitors - especially with notebook computers.

With high end interfaces on laptop, I find I frequently have to use transformers to connect to FOH systems to eliminate noise problems. I use a variety of ebtech and Rapco boxes designed for this purpose (as do most sound engineers), depending on the connectors needed and whether they have to transform levels. I carry about 12 such various devices with me in my FOH kit.

I'm not sure I understand what advice you're looking for here. I suggest a little trial and error.

By all means buy an interface you like the sound of - that's up to you, but you may find it still doesn't come with cabling ready to plug in on a stage without some kind of isolators - and you still can't connect one interface to two computers - you'll need to buy two.

Actually, I suggest asking the sound engineer at the venue (or venues) you have in mind what equipment you'll need. Only he can tell you what he needs you to provide and ultimately you need to work with what he's got on his end.

M

Edited by mpvano (27/11/12 11:48 PM)

Hmmm....

While sitting at dinner I had a moment of inspiration!

I figured out how you CAN use just one sound card!

This approach may be more suited to the way you are thinking about the problem or may give you some more ideas about how to solve it.

MacBooks have digital optical SPDIF output built in via 3.5mm toslink.

If you buy an interface with good "cue mixing" support you might be able to feed the audio from the second Macbook into your interface's optical input and mix it with the audio playing back from the machine the interface is connected to.

This would let you get by with one interface and if you should need them, one set of isolation transformers. If you start with an interface with good enough balanced XLR outputs (e.g. an MOTU 828 or similar) - you may not need them at all.

This approach lets you do all d/a conversion in the outboard device's converters.

Because only one device is coming in digitally, you shouldn't have to worry about sync.

I've used various macbook digital outputs and they work quite well.

I've done something similar to this via one of my Edirol interfaces (but for a completely different reason). However it's 1/4 inch outputs usually need isolators when used live. I didn't care about latency, so I mixed the two audio streams using Cubase's record monitoring facility.

If you have a macbook with separate in and output jacks, you could even do the mixing in the macbook (e.g. in Live or Cubase or whatever is generating the output on that machine) and all you'd need is an external standalone D/A converter.

seriously - I hope this helps give you some more ideas - good luck with your project...

M