I'm looking around at what kind of mixer to get for a small band PA. One thing that comes to mind is that mixing for live performance generally seems to be more a question of "dual mono" output than true stereo. ie, the same mix is sent to each main monitor, so you don't have the people on each side of the room hearing an unbalanced mix. Correct?

So, when using a "normal" mixer that was not designed specifically for live use, like one of the mid-range Spirits or Mackies, how does one go about this? Is it simply a question of panning everything dead centre so the L & R outs are effectively the same, and then sending them out "as though" they are normal stereo outs, to L & R monitors? Or is more complicated jiggery-pokery required to sum the outputs to mono first, etc, to do a proper job?

And do specialized live mixers have different bussing and routing structures to achieve this?

Thanks.

You don't need any specialised mixer to use if for a 'mono' solution, you do exactly what you have said and keep all the mono channels with the pan pot in the middle.

You may run into problems with the stereo input channels if you don't take a single mono feed into them, but all the stereo channels I've seen on different mixers have one input of the pair as a mono option. So just make sure that any keyboard feeds are from their mono rather than stereo outs. Many keyboard stereo feeds can be very heavy on the stereo imaging with all the bass notes in one channel and all the high notes in the other, which makes for a very large virtual piano when you've got speakers 25'-30' apart, so you are best keeping these mono anyway.

If you use any FX such as reverb, either built into the desk or from an external unit via aux sends and returns, then these will normally be in stereo but will not affect the overall 'centre' imaging to any extent where it becomes unbalanced (unless you use ping-pong echos or auto-panning - in which case you are going for a stereo effect anyway).

If you are really paranoid about keeping it mono, then most two-channel power amps have a mono option where both channels run from the same single input feed and so you are guaranteed a mono sound if you only take one feed from the mixing desk. Many mixing desks these days have a mono summed output which can be used to feed a sub, often with a switchable low pass filter. With the filter out, you could use this to feed a mono system if you really want to as well.

So loads of options and no need for a special desk!

Thanks, that sounds easy enough.

I'm the keyboard player and my keys actually run through a couple of effects units "in line" - ie, there is a single stereo out from each of the two units that contains the whole signal, with the appropriate amount of reverb, delay etc added, rather than a send and return situation with separate dry and FX signals.

I've always just given these stereo outs to the mix engineer and not taken much notice of what he does with them. How would I best go about integrating these into the mono mix? Would I be better off taking them out of the FX units themselves in mono? Presumeably that would lose a lot of the reverb quality, but then I suppose that's going to be lost anyway if the keys are made mono in the desk.

You've got two choices as I see it. Either just use the mono FX route as you've said, or you can feed the outputs into two mono channel inputs and balance them slightly left and right - nothing too excessive but just enough to give some stereo width without having too much come out of one speaker or the other. If your keyboards don't produce too drastic a sound spread you may get by perfectly happily by feeding into a stereo input channel.

You could somehow contrive to get a straight mono keys feed to the desk as well as your stereo FX. The sounds would then be balanced at the mixing desk so you got the straight keyboard sound in mono but the FX in stereo. The FX would have to be mixed a lot 'wetter' in this instance. Plus it all sepends on the type of FX you are using. If you are using a lot of delay to produce repeat notes that are a main part of the song, then it might be better to keep them in mono.

If your stage set up isn't too wide and your speakers aren't too far apart, then there shouldn't be too much trouble with a stereo mix and FX anyway, as long as the balance isn't too extreme. You just might have to adjust your FX for a live situation in comparison to the way you have them set up when recording or rehearsing at home.

Hopefully you'll get some feedback from people who've done this at a professional level and will say what they do (rather than my experience at pub/function level).