Did You Want A Sub, A Sub, Or A Sub?

When I started writing this article, I quickly realized how much the word "sub" gets tossed around in bands.

It can mean a speaker system designed for low frequencies, as in "I can't feel the kick drum...turn up the subs."

It could refer to a replacement musician...."Louie got busted again and can't make the gig, so we'll need to get a sub on cowbell for the night."

Or, it could simply be what the drummer had for dinner.

But today, we'll be referring to the term in the context of sub group on sound board.  

Explain This Again
So first and foremost, what the heck is a sub group?  In it's most basic form, it's a way to control a large number of channels with one or two faders.  If you were looking at this from the stand point of signal flow on a board, it would look something like this:

OK...easy enough.  But why would you want to do that?  Let's say you've got a drummer with a fully mic'd up kit.  That can take anywhere from 6 to 12 (or more) inputs on the board.  After you get the EQ on each drum set, you're going to balance the levels of the inputs with each other.  So now you've got a balance between all the mics.

Then you start adding in the other instruments, and you quickly find that the drums are getting buried in the mix.  Sure, if you're careful you can grab a bunch of the channel faders and push them up.  But, if you had routed the drums to a sub group then you could just grab that fader (or faders if you're doing the drums in stereo) and adjust from there.  You're changing the overall level of the drum kit, without affecting the balance between the mics.  And when you're mixing during the show, it's a lot easy to do and not mess up the balance.

What's Good For The Drummer...
...is good for any other groups of similar inputs where a balance needs to be maintained.  After drums, I usually sub-mix vocals next (even if there are only 2 vocalists, and I'll explain why in a bit).  Sub mixing the vocals gives you an easy way to turn everyone up and down while again keeping the balance.  

In fact, taken to it's logical end this is what I might do on a mono system with 4 sub groups.

To Sub Or Not To Sub
You'll notice on the diagram above that not everything is routed through a sub group, namely the bass and lead guitar.   This is based on only having one mic or DI on each of these, so it's only one fader to deal with.  Back in my days of excess in the late 80's I had this ridiculous bi-amplified stereo bass rig that took up of 4 channels on the main board (Pre-effects DI, Time-based DI, and 2 mic'd cabinets).  That was a prime candidate for a sub group.

Horn sections and percussionists are also perfect for sub groups.  

But Wait, There's More!
Having the convenience of turning multiple channels up and down is cool, but with a sub group you also have the option of applying processing to the group.  The most common is compression...especially on a vocal group.  And here's why it's cool...if it's set up correctly then your system will just about mix itself.

Let's look at what happens without group compression first.  You have the vocal mics set up where each mic sounds good through the system and the the level is balanced against the music...not too much but not lost in the mix.  That's fine for when you have only one person singing, but what happens when you get to the part of the song where there's a two part harmony.  Now the vocals are a little further ahead of the music than desired, so you either turn up the instruments (bad news...because you just started the upward volume spiral), or you have to turn down the mics.  And now, the harmony part is over and your lead vocalist is buried.  There's got to be an easier way.

Captain Compression To The Rescue
If there was just some way to automatically adjust the volume....oh wait, there is!  This is precisely what compressors were designed for...automatically controlling the volume (in fact, they were first referred to as A.V.C.'s, or Automatic Volume Controls).

Some boards now include group compression (Carvin, Presonus, and others).  But almost every board has an insert point on the sub groups.  Patch a compressor across the vocal sub and set the ratio at 3:1 with a threshold of 0dB.  What you want is just a little compression on one voice (maybe 1 or 2 dB), 2 to 4dB for two-part harmony, and up to 6dB for three-part.  What happens then is that as you add harmonies the vocals get a little louder, but not too much.  And as a result, you shouldn't have to jack with the vocal levels throughout the night, at least until the lead singer gets drunk and starts forgetting the words...they bury him in the mix.

Moving In Stereo
If you have a sub group that you want to spread across the stereo field (drums, keys, etc), then you'll need to route to two sub groups.  Those, in turn, would get routed out left and right to the main bus on the board.

How you do this varies from board to board, so this is one time where I would encourage you to read the manual that came with your gear.  But, in general, it's a combination of routing buttons and a pan pot on the channel (digital boards...way different most of the time).  

Let's look at a close-up of a photo from last week's installment:

 

You'll notice that the bus assign switches are paired up 1-2, 3-4, and L-R.  If you select the L-R, you're going directly to the output and bypassing the sub groups.  Useful for the bass and lead guitar, but let's say we want to set the drums up in stereo so that when the drummer does the huge Neil Peart 6-tom fill from high to low it moves across the stage.  We'll pick sub groups 1 & 2 for the drums.

So, you would select the 1-2 button.  Then, don't forget on the sub groups themselves to assign group 1 to Left, and group 2 to right.

If you're trying to do stereo, don't make the mistake of selecting both Left and Right on both sub groups.  You've just mono-ized yourself.  (If you're using a single sub group or running all of them mono, then yes...you would select both.)

Now, go back to the channels for the toms and adjust the pan pots.  If your drummer is right-handed and sets his kit up in standard configuration with his high toms on his left and floor toms on his right, then you're going to want to pan just the opposite.  In other words, pan the high toms to about 2:00 on the right, and the floor tom to 10:00 left.  Then split the difference between the rest of them.  Overhead mics (if you're using them) can go 9:00/3:00, but I wouldn't pan anything wider than that.  Just make sure you've got things panned so that the sound lines up with what the audience is seeing (unless you're just wanting to jack with 'em).

I've got to give props today to a gentleman named Dave Rat, who runs Rat Sound out of Oxnard, California.  Dave started out cobbling systems together in his back yard, and now supplies sound and Front Of House engineering to bands such as The Red Hot Chili Peppers, The Foo Fighters, Pearl Jam, and others.  It was Dave that turned me on to the idea of group compression.  He uses it just like I described (except with 24 sub groups and 12 stereo compressors).  We should all have such problems.

Next week, I'll be missing in action.  Our cat Spot will be answering the phones and replying to email while I'm out.  

Until then, keep the meters out of the red!

Ken

Ken Carver has been a musician and performer since the early 70's, and involved with live music production since the mid 70's. He worked for 15 years as a broadcast engineer, building numerous studios and transmitter sites around Texas. He's also worked in Critical Care Communications for the medical industry, R&D for an automated lighting manufacturer, and owned Project Lighting & Sound in the 80's. He currently heads up an R&D Hardware Technician Team at National Instruments in Austin, and still performs on the weekends in the Central Texas area. You can reach Ken at itsjustlogistics@gmail.com