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Analogue gain and digital trim on digital desk

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Grubbah View Drop Down
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    Posted: 15 October 2014 at 12:55am
So what's the crack...

Gain up on analogue gain nice and hot to utilise pre-amp / bit rate and maximise S/N ratio, set faders at unity and alter levels using digital trim from then on?

I work a mainly with analogue on a midas xl200, so used to slamming gains hot, faders at unity and mixing on my VCAs.. However more and more digital desks are coming through and trim is a new game for me.

Obviously I can't run red hot with most digital desks like the midas (which sounds great doing so), but in principle the S/N ratio theory is still the same?

Edited by Grubbah - 15 October 2014 at 12:55am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jimmer Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2014 at 9:52am
Never understood people setting faders at unity, but see it a lot? I have always set gains/trim to 0dbu or roughly -24dbfs to achieve a good gain structure. then I use the faders to balance & mix my sound. Happy to be corrected or understand the reasons behind this, but why do people set the faders to unity and use gains to balance the mix? Is this something that has come in on digi consoles? Surely your gain structure would be all over the place?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Grubbah Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2014 at 1:01pm
Some of the benefits for mixing at unity includes more accurate attenuation of level at '0'. For instance the distance between -30 and -10 is the same as 0 and -10 (or something like that). Also Channel faders will alter outgoing signal to processors, like compressors, so effetely can alter your gain structure further a field.

However Im also not a fan of riding my gains, as you say it can lead to improper gain structure. Also if you are providing monitors from FOH, you're going to alter everything!

On an analogue perspective I tend to do both. I gain up to a good level to optimise the pre-amps / SN ratio and I set each fader at unity. Each group of of instruments is then controlled by a VCA. For instance a basic typical set up would be;

Drums / Toms / Bass / Guitar / Vocals / Whole Band / FX

I then use my EQ to balance instruments against each other. For example, before Snare Top and Bottom in soundcheck, I will ask for Hi-Hat and leave the channel un-muted whilst I move on to my 2 snare channels. It gives me the opportunity to manage and EQ the bleed from snare into the hi hat mic without jumping for the channel fader as soon as a full kit kicks in.

Once everything is checked, my gains are optimised and my board is sat at unity and I rely on my VCAs for the house mix. A good band with a good stage volume and no acoustically problematic instruments (like smashing the granny out of cymbals) will generally see a consistently set unity board over onto my VCAs. What I usually expect is to bring my "Whole Band" VCA down by about 5dB and push the vocal up by 5dB. If one guitar cuts through more than the other (or any mic line for that matter) I try to refer to the EQ or perhaps notch the channel fader down (though I rarely find myself notching down more than say 3dB).

From what I understand about VCAs, they don't product an extra output stage like a sub group, but instead relies on altering voltage between summed signals... So effectively doesn't effect the integrity of your gain structure and has no adverse effects on external processing and the likes. So providing system is calibrated well in the signal chain, you will be able to produce a decent output signal from your desk in the above manner. 

Thats my theory...?

Can the same idea can be implemented on a digital domain? Does digital trim offer attenuation without effecting the integrity of your gain structure or effecting other elements of the mix? Therefore can you optimise your pre-amps using the analogue gain, keep faders at unity to maintain your mix and then freely attenuate signal using the trim..?


Edited by Grubbah - 15 October 2014 at 3:32pm
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Phil B View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Phil B Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2014 at 1:53pm
Main reason I use digital trim is if I`m gain sharing with another desk / output.

Normally it` s a Midas setup with 2 x desks and 1 x stage box. Usually one desk will take head amp control and set that gain then you can copy the AES50 audio to another desk / output, they then set their own  digital trim if they are not happy with their gain structure? 

Same kinda thing with Digicos and I believe the Behringer X32 ??

I`ve used it occasionally on a Midas to hit the pre-amp hard ( bass gtr,  etc) and then pull it back to normality for mixing...kinda like analog but kinda easier !

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Grubbah Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2014 at 2:20pm
Originally posted by Phil B Phil B wrote:

Main reason I use digital trim is if I`m gain sharing with another desk / output.

Normally it` s a Midas setup with 2 x desks and 1 x stage box. Usually one desk will take head amp control and set that gain then you can copy the AES50 audio to another desk / output, they then set their own  digital trim if they are not happy with their gain structure? 

Same kinda thing with Digicos and I believe the Behringer X32 ??

I`ve used it occasionally on a Midas to hit the pre-amp hard ( bass gtr,  etc) and then pull it back to normality for mixing...kinda like analog but kinda easier !

.p.

This Is essentially what got me thinking, the other night I was mixing support on a pro 1 that shared a stage box with a pro 2 on monitors and exactly this was the scenario. 

Im happy with my approach towards analogue desks, its how to then implement this onto a digital board is where I am questioning things.







Edited by Grubbah - 15 October 2014 at 3:00pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote azlan Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2014 at 2:56pm
the theory behind setting faders to 0 and then dialing in gain seems to be to achieve a couple of things, first off, it means that it is relatively simple to chuck together monitor mixes (as you can chuck each aux send to 0 as well and have a decent starting point) when mixing festival style.

secondly, you are mixing in the 'sweet spot' on the faders as they are usually logarithmic, and have are less sensitive around 0db than anywhere else on the fader, meaning that you can make more precise changes to the mix more easily. Having the mix roughly right with all the faders at 0 means that everything can easily be tweaked and tuned on the faders. It can also stop people running out of headroom on the fader if it keeps getting pushed up to sit over a mix.

Digital trim is usually used when splitting channels (to mons, broadcast etc..) so one tech sets the main HA gain, which is then locked off (unless there is a major reason to change it) and everyone can tweak these (now line level) signals in their desk to suit their needs.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dymondaudio Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2014 at 3:28pm
Originally posted by Jimmer Jimmer wrote:

Never understood people setting faders at unity, but see it a lot? I have always set gains/trim to 0dbu or roughly -24dbfs to achieve a good gain structure. then I use the faders to balance & mix my sound. Happy to be corrected or understand the reasons behind this, but why do people set the faders to unity and use gains to balance the mix? Is this something that has come in on digi consoles? Surely your gain structure would be all over the place?

This is precisely the way I do it also.  Never understood mixing with gains, even on a digi desk unless there is a separate mons desk, mixing with your gains will change all your monitor mix levels will it not?

When I got my first 'propper' desk (many years ago) which was an Allen & Heath GL2400/32 I remember reading their take on mixing with gains and thought "I'm glad I think the same as A&H"

I appreciate that some of what they're saying is opinion, on the whole I still agree with it.

Quote Allen & Heath:

"Mixing with faders or gain controls?"
There is a technique used by some operators where they set all the faders to '0' position and balance the mix using the channel gain controls. We do not advise this method as the signal to noise ratio and control resolution can be severely degraded.  In addition it is impossible to mix monitors from FOH in this way as it changes to the gain settings affect the monitors too.

The correct method is to use GAIN to match the source to the operating level of the channel for optimum dynamic range, and then use the FADERS to balance each source into the mix. With correct system gain structure, prime sources such as vocals would have faders operated at around '0' while sources low in the mix such backing vocals and acoustically loud brass and drums would display their true contribution with their lower fader positions.  This is a much more accurate and visual way of mixing."
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Post Options Post Options   Thanks (0) Thanks(0)   Quote burningbush Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2014 at 4:20pm
I am with you Jimmer (the King Star), I fly my desk with the faders.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jimmer Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2014 at 4:30pm
LOL Jimmer the King! this could get out of hand!!

It just seems the most logical way to me to fly with the faders.... but you maybe right, young guns with new tricks?

Edited by Jimmer - 15 October 2014 at 4:32pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJordan Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2014 at 4:32pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goodvibetribe Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2014 at 4:38pm
I've also never understood why people mix on live desks with all the faders at 0. Everyone has their preferred methods of mixing, none of which are 'wrong' if you still get good results, but doing that has just never made sense to me. It almost makes the point of faders redundant, you may as well have pots there. Dynamics of the input aside, the max level of the input should remain a constant (although not always the case if you have unprofessional musicians) so I use the gain control to make all the inputs the same level, then use the faders to balance the sound and create the mix. Then use vcas/groups to control groups of inputs from there onwards. The only time I 'mix' on gains would be if im DJing rather than mixing bands, when the max input level of the tunes can vary sometimes and isnt a constant. I still move the faders to bring tunes in and out and always have all the faders at max when a tune is playing, then use the VU/listen to the track im about to bring in and match the gains of both tracks.  

The Midas Digital desks, like the analogue ones, still sound better if the pre amps are driven hard and In my opinion this even rings true for the x32. As people have mentioned, digital gain is for when desks share the same preamp.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MattStolton Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2014 at 4:49pm
Errm - I PFL each channel, and set gain to give me 0dB ish peak on VU. Typically then Ch Fader will be somewhere around 0dB +5/-10. Means Aux has 0dB running to it (pre fader) for doing mons from FOH. Watch the Ch VU in case someone lets rip between sound check and performance.

I do the Dave Rat publicised trick of a 8 Ch Comp on the 4 St Groups (On my Analogue GL2800). Gr1/2 is drums, Gr3/4 is instruments (Typically Guitars), Gr 5/6 is other instruments (Keys), and Gr 7/8 Vox. Simply compress the Vox group less, and they pop up in the mix, say 2:1, whilst everything else is compressed 3 or 4:1. No group then peaks and clips, and spoils the master running at 0dB, everything runs at around 0dB, and brain sound perception gets the Vox heard in the mix. If you need to let a solo guitar to get out of the mix more, simply tweak its group comp down in ratio a bit for the middle eight.

On a digi, with everything having a full outboard processing rack per channel/X-point/O/p even easier, and it works nicely for my ears.

So I'm with "the king", and Allen & Heath, which happens to be what I often use (GL2800 and GLD)

If I had proper splits, and budget for a Monitor Desk and Engineer, then there may be some merit, but I doubt I will ever be on a job where client has budget for both a FOH and Foldback engineers, let alone second desk, etc.....
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