Friday, March 23, 2012

Guest Post: Karl Maciag - Beyond The Mix

Karl Maciag is in the system design line of work these days but used to push faders out in venues.  Now you reap the benefit of his years of experience.  Karl also writes his own blog over at Karl's Empty Space. Click on the Contributors link above to see his other posts on this blog.
Devilicus Handsomicus
Previous posts from this series:
The Mix - Part 1
In a previous entry, we ended with audio going out of our console to processing an amps, and then speakers. I’m not going to contribute to the continued bludgeoning of the dead horse named “this DSP, amp, speaker system is best”. I think I’ll delve more into a philosophy and approach to how I use these tools, concentrating on DSP the most.

What is our goal of using DSP to manage a speaker system? It should be that the DSP is used to make the speakers sound natural enough, that you can’t tell that the original sound is being amplified. This is much easier said than done. There’s many things that the DSP can’t fix. Room modes are one. Stage volume is another. Changing temperatures and humidity during the course of the show. In our world, we are constantly in the pursuit of perfection, but only achieving the best possible result, given the conditions. I’ve never met a system tech that said “OK, this is perfect, there is nothing more I can do.” If he does say that, he’s a liar. Can he get close? Sure. I’ve heard some great engineers do amazing things with speaker systems. But none of them say it’s perfect. Do your best, but accept that you’ll have to stop tweaking at some point, and continue with the show.

We don’t always have access to the crossovers when we walk into a room. If you have your own rig, you have the ability to play, so go ahead and push buttons. With the crossovers, chances are your speaker manufacturer has some specs published somewhere on what frequencies the drivers of your speakers should be crossed over at. Use them. There is a ton of R&D done by a ton of guys that are way smarter than us, that test things much longer than we can to come up with these results. Give them a call, and get a recommendation on what to do based on the processor and amps that your have. They’ll be happy you called.

Where I like to start helps with the overall gain stage of the system. I’d be remiss if I didn’t thank my good friend Joe for showing me this method many years ago. I do not like to compromise running the console at 0dB. If it’s too loud for the room to run the console at 0dB, I will adjust the gain in the DSP. I do not start with the input gain. I keep that at 0dB too. I do not adjust the amp levels either. Typically
amp volume knobs are input controls, not output controls. I don’t want to limit what I can put into the amp, I don’t want to limit that headroom. So, I mute all my bandpasses. Let’s assume we have a 3-way system that we are working with. I run program at 0dB through the console. Starting with the subs, I bring up the sub output of the crossover until I feel it’s loud enough. I mute the subs, and do the same with the mids. Then I mute the mids, and do the same with the highs. Then I turn them all on. It should sound somewhat musical right away, and not be ripping heads off. I might make little adjustments, but this is my starting point. Running the desk at 0dB should give me this volume.

Keep in mind, when I do this, I don’t have any parametric or graphic EQ active in the system, this is running flat. Also, my program material is material that I know the tone of very well. And it should be music that is clean sounding, and covers the frequency spectrum. I was on a tour and the headliner’s engineer used Peter Gabriel’s “Sledgehammer”. Every day. I heard that song every day at the same time. And the show sounded the same every night. That consistency came from tuning the systems with that track, regardless of what gear it was. I would recommend going with a pop record that you’re not embarrassed to listen to in public.

After I have my basic crossover levels set, I start to EQ the system. Typically I prefer to use parametric EQ, so I can adjust the bandwidth of the filter. Graphs are fast, but the Q is fixed, and adjusting a fader does effect the faders next to it. Pulling out 9dB of 315Hz is going to effect the gain of 250Hz and 400Hz as well. With a parametric, I can fight that to a degree. When I’m tuning at this point, I am not listening for what the system is lacking. I’m listening for what is too strong in the system. If I can’t identify the frequency right away, I’ll sweep the parametric until I find it. I’ll narrow the Q, raise the gain, and sweep. When you hit that frequency, you’ll know it, it will howl through your head more than the other frequencies. I then reduce the gain of the frequency until it sounds balanced with the other tones happening, widening the Q a bit as well. With a graph, I quickly move the faders up and down, looking for that same effect of the ugly frequency howling in the room. If it’s a wide range centered on one frequency, I might pull the center one down a bunch, and then the two adjacent faders a little bit too. Play around with it. My goal doing this is to get that source material sounding in the room the way it sounds to me on my headphones, or speakers I listen to all the time. If you have parametric in your DSP, and a graph in your rack. I would set the DSP with the parametric to get your system basically flat, and then make little adjustments with the graph as needed. This is helpful if you have visiting engineers on your system, they can adjust the graph however they want, and you can just bypass it to mix the openers if you don’t like their settings.

Remember, you are controlling gain with the EQ. If you’re scooping out massive amounts of mids with the EQ, you’re going to running a lot quieter than you wanted. I shouldn’t have to say it, but smiley faces aren’t acceptable on a graph. Go do lights if you want visuals! After I tweak the EQ, and the program material sounds the way it should, I’m ready to start hearing the band…

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