Mixer master fader v active speaker volume

flying_pie

I did my first gig in more than 3 years at the weekend and noticed at the break that the sound guy had the master fader on the desk way down - probably around -18dB  - and presumably the PA speaker volumes set loud. We were all DI except drums and the report from the crowd was that the sound was good so no major concerns but a couple of experienced guitarists in the crowd mentioned the guitars weren't quite as strong in the mix (not something that we find in rehearsal where I do the desk).

Perhaps it's just down to the sound guys preference compared to guitarists in the crowd.  I had plenty of guitar in my monitor so had no worries but it left me wondering... It felt odd to see the master volume really low. I'd always learned to set it around unity provided the overall mix isn't too hot and then adjust the speaker volumes as it makes sense to have a strong enough signal going to the speakers rather than greater amplification of a weaker signal.

Is there any significant effect to the overall end sound between the two approaches? Or is it so negligible in your average small venue as to not make a difference?

Winny_Pooh

In a venue acessing the powered cab's individual volumes may not be easy mid gig so it makes sense to set them relatively wide open (unless the power smps are particularly hissy at high levels) and have the output from the mixer below unity. Leaves volume to spare later on in the gig if you bump up the master fader, sufficient headroom for the speakers/powered amps and doesn't affect the input gain/noise level of the individual channels in the mixer section.

maltingsaudio

Active cabs volume should be set to 0db then adjust from the desk, it is all too easy to overdrive and blow a system if volume of the cabs is set too high. Check the manual of your cabs to see where 0db is on the volume control. Then mix with your ears listening  for distortion and don’t trust exclusively what you see in the meters 

Stuckfast

Makes sense to leave plenty of headroom on the mixer. You don't want to be running on stage to turn the speakers up mid-gig.

shufflebeat

This has already been implied but not spelled out::

if you have a speaker volume too low and the mixer turned up beyond “ideal” to compensate then you’re likely to push some element into clipping, either a channel, group or master output.

what actually happens in clipping is that signal reached maximum capacity at a pinch-point but upstream the signal keeps rising. Because the pinch-point can't relay any more it just sits at max. Then this gets passed on to the amps.

Anyone who has played with a pendulum of any size (tyre on a rope?) will know that when a system wants to return to balance there are often relatively huge forces at work.

The speaker gets pushed out (or back) and is then held there as the pre-amp signal has flatlined at max, the speaker can’t return to rest an onto its next cycle. This puts massive strain on the voice coil which is likely to warm up, deform in its narrow channel and grab the sides, or just melt.

So keeping the speaker volumes too low can be just as damaging as too high. Good gain staging throughout is the secret.

Danny1969

Was it a digital desk or analog ? 

With analog gain structure is more important as every EQ section and additional bus adds noise. Plus analog mixers tend to lose high end detail. So people generally shoot for a higher PFL level with analog .... then you  generally  keep the master fader at 0db and get the mix volume from the channel faders. However in some systems you might find you are in the lower portion of the channel fader all the time and mixing involves too small a movement. So lowering the master fader allows you to increase move this mix position further up the faders. 

Then of course, for a given input  (normally in 1Khz sine wave reference) some mixers have an output level of 0dB which is 3/4 of a volt over 600R, some are +4 which is more like 1.2V ... so basically some mixers will be louder than others into the same amplifier or active speaker. 

There's no standard with today's active PA speakers. Some are switchable to line or mic level, some have a gain pot which is usable for a mic plugged straight into the input with the gain whacked right up. Some are unity gain at halfway, some are only subtractive and unity gain is whacked up full. 

With digital the PFL is more forgiving because you can do a lot of processing without adding any noise and they don't have the high end roll off. But once the mix has hit the DA convertors on the master bus it's just a voltage waveform jumping either side of 0V and no different from the output of an analog desk. 

So it's really about knowing the signal chain and which bits have the headroom bottleneck. Then there' still loads of ways to mix. It's very common on digital desks to just setup VCA's for drums, guitars and vocals ... especially with ipad mixing as it gives a fair bit of control with very limited swiping 

flying_pie

Thanks everyone. That's really helpful in the minefield of information that is mixers and signal chains.

FWIW it was a digital desk - QU-16. As I was saying it just seemed odd to see the master fader very very low down indeed rather than a few dB. Makes perfect sense though

Danny1969

flying_pie said:

Thanks everyone. That's really helpful in the minefield of information that is mixers and signal chains.

FWIW it was a digital desk - QU-16. As I was saying it just seemed odd to see the master fader very very low down indeed rather than a few dB. Makes perfect sense though

You might not have been looking at the master fader ... that fader can be anything on a QU16 , Aux 1 master level, Aux 2 master level, Effects send 1 master level, Effects send 2 master level  etc

Some engineers will leave that fader set on an aux send master that's controlling a wedge so they can just grab it in case of feedback ... particularly when a singer bends down with the mic towards the monitor.