Gain Structure ?

[musicman7722]

Hello

This weekend I had a gig and our old sound man was there with is girl friend.  He mixed us for 3 years and is now just doing our larger gigs.  I asked him to tweak the system and showed him how the ipad and software worked.  He did a good job but one thing he did was turn down most the the channel gains as he said they were peaking.  Except for the kick and snare I don't recall seeing them peak much at all.  When he did this he was forced to run most of the channels near max.  So my question to the group here is is do anyof you run your board a bit hotter than other boards?

I seem to have lost a fair amount of headroom/volume now.  I run QSC K10 tops and a single KSub.

Thanks

Chris

[Greg C.]

When you say "peaking", do you mean actually lighting up the red LEDs on the inputs?

[musicman7722]

I am saying that I rarely see them hit red so the answer is yes (I think).  If and when I do seem them in a consistant manner I will slowly back them down and then increase the channel volume accordingly.

[Greg C.]

According to the specs, the lights actually go red at 3dB below actual clip. Based on that, tickling them once in a while is probably ok. One of the things that drives me bananas on the Avid Venue consoles is that the default clip indication is on their channels and buses is 6dB below actual clip which really does eat into your "apparent" headroom. The first thing I do when I get on a Venue is set the clip indication to "0dB" where it should be. At least for me, I want to know when I'm actually clipping rather than lied to.

In any case, if you feel that you've lost headroom as a whole and aren't comfortable with occasional red lights on your inputs, by all means increase the gain at your speaker processor/amp/powered speaker inputs to compensate. I do that on my setup when I switch between mixers that have different max output levels. As an example, if I'm using a desk that has a max output level of +21dBu like the DL vs. +24dBu max out on my Venue, I'll boost my speaker processors' inputs by +3dB to compensate so that I'm not hammering the mixer to get max output of the speakers when needed. Conversely, If I have a Mackie analog mixer plugged into the system with +28dBu max output, I'll attenuate the processor inputs by 4dB to keep things matched up.

[WK154]

Hi Guys, are we inventing a new Mackie view of gain structure?
"I seem to have lost a fair amount of headroom/volume now. "
This is a digital mixer and Clip is at 0 dB FS which in the DL is 21 dBu. When you lower the preamp gain as in your case you increase headroom not loose it. You also decrease S/N ratio, a bad idea. The RMS of your music should be around 0 on the channel scale which on the DL leaves you 21-6 dBu or 15 dBu headroom in theory. The problem as I pointed out before is that Mackie's representation of signal values can be off as much as 10 dBu depending on where on the scale you are. The amount of headroom that is required depends on your music. My experience in recording Bands, Orchestra's and Choirs indicates a crest factor (the difference between RMS and Peak value of you music) of no more than 12 dBu. That should leave you 3 dBu before you will ever reach clipping. Read Bob Katz's view of the Loudness wars. This of course depends on mic placement and ultimately your instrument balance. If you exceed 15 dBu then you need to look elsewhere for the problem. P.S. volume is for beer.

[musicman7722]

Thank you each and everyone

[prosoundco guy]

Something I've noticed: you will get a peak indicator light on the iPad channel strip, then when you look on the board at the clip light by the trim/gain knob, it's not clipping at all. Guess that's to get you attention, but I may start to ignore it. I run pretty much all channels in FOH roughly at unity gain. The master stays at r just above unity. 

[WK154]

That's because the visual bar is at 10dBu and clip is at 19dBu. All screwed up. I think Elvis had a song for that.

[musicman7722]

Gents

Well it happened again so let me review what I think is correct and then you can congratulate me or correct me.  First off in this scenario there is no comp or gate on on any channel nor on the master outs.  Again this weekend a tech mixed us and the first thing he did was zero out my trim pots.  Meaning he turned the trim pot on every channel to U which to me means all the way counter clockwise.  I flipped out and actually had words with him.  I have been nursing those trim pot settings since the last guy zeroed them out.  I only use the mixer for my band.  So he did the usual line check for each channel until they peaked (on the channel strip not the physical trim.  A little history as well, he is the guitar players 21 year old son and fresh out of sound school, whatever that is.  He is full of "dude that isn't going to happen" sort of comments.   I shrugged and played the gig.  I reviewed the settings today on my board and the sob had the gain on my bass channel at U.  Wow he sandbagged me .  anyway he had the trims so low that he was running the kick and every vocal above 0, wow.  So who is right on this board, them or me?  If it's them I am going a need much louder tops then 2 K12s and 2 K12 subs.  Incidentally for this gig we had two QSC KW12's.  Heck it was even tough hearing my IEM because the gain was so low on my bass.

Please educate me. 

TY

[WK154]

First send the "dude" back to a better audio school. The equipment is well matched unless your doing some heavy metal or similar stuff. Venue size will determine whether you have enough power and that of course varies. You need to understand the equipment before you can adjust it properly. The DL has issues with what you are really looking at. Let's start with the preamp (trim pots) adjustment. The meters on each channel are input PPM meters. What does that mean? The meter bar is indicating the peak loudness level not the average and reaction time is in milliseconds (refresh rate of meters actually). I once asked Mackie to provide a red line for max peak with a duration of 1-3 seconds persistence, like many other programs such as Audacity. The trim pots (your point of contention) should be adjusted once for the mic or other gear with the expected average loudness that you would encounter with the respective artist. The average should be at scale of "0" this gives you 15dBu of headroom (actual measurements). Yes lots of yellow and some red, you can't see this without an oscilloscope. This is something for rehearsal or extensive sound check. You can't do this with stupid "Check..Check...Check" or any other phrase I hear so often. Professionals set this once for the artist/equipment combo. It is not for mixing! This is why I and many manufacturers place less value on trim pots being automated especially with a single Band with the same artists. You should find your best settings in rehearsal and mark them, channel setup done. This also goes for eq's and any gating and compression. An important aspect for this to work consistently is mic placement. It needs to be consistent as well.  These settings have nothing to do with room acoustics, that's for output channels. If you're using IEM's I would recommend using compression as a limiter for those surprises you didn't expect. Then of course comes the balanced mix (faders for this) along with output channels and those settings for room acoustics. Main fader near 0. K series attenuation/gain adjustments will determine room loudness.

[musicman7722]

WK154 

Thank you for confirming what I have learned over the years.  I adjust the trim as I go slowly bringing it up during the the first gig to where it barely hits read on a loud passage, then leave it alone unless something radical changes.  Kick and snare are the most obvious instruments for that.

Also I agree with IEM ans my Sennheiser G3 has it built in and adjustable.  I just wanted to make sure nobody reading this thought my issue might have been the comps.  I spoke to my guitar player and he said his son was quite upset.  I let him know I would apologize at the next gig for the sake of peace and harmony.  He is mixing us again this weekend but using a mixer with real nobs and faders which he prefers.  I have a splitter snake so he will not be touching my rig.  Funny you would think somebody so young and new to the trade would be psyched to get hands on with wireless digital but he wants to use a beat up mackie 24 channel board that is used by 5 bands a week.

Oh well.  Can't teach an old and sometimes a new dog tricks.

TY Again

[WK154]

Clip on the DL is at 21dBu (0 dBFS measured with scope and steady sine wave signal) but the clip light triggers at -6 dBFS or 15 dBu (measured) not what the manual states (-3dBFS). Most of what I measured music wise runs 12 dB crest factor or less, that leaves at minimum another 3 dB before clip. What puzzles me is that the basics were apparently missed in audio school and it's not going to change with the analog mixer. There was a time where the Mackie mix bus section of the analog circuit would clip prematurely and it necessitated cutting preamp gain, until it was fixed in a later model. Certainly not a mixer to learn on. Proper gain structure it seems is a difficult concept to get across.