A long time ago, in a land far away, a system processor in an installed PA was a 15- or 31-band graphic EQ or three. If the system had some delay speakers, there may have also been a delay unit or two in the mix. Things were simpler then. At some point, loudspeaker processors came on the scene and were able to do cool things like signal routing, EQ, delay and limiting. Today’s DSPs are truly powerful boxes that do all that and more.
Back in the day, we typically didn’t even have output EQ on the console, so some form of EQ and or timing was required between the desk and the amps. Larger boards may have had several matrix mixes that could do some gain shading, but for the most part, the console sent a mono or stereo mix to the processing. We’ve been doing something similar for with DSP systems as well.
More and more amps are arriving on the scene with plenty of processing built in. And sometimes, depending on the situation, that can give you more than enough horsepower to get things sounding tasty.
But the question comes up now, with all those powerful processing blocks available at the console level, do we even need a system DSP? Like many things in audio, the answer is, “It depends.”
You Don’t Need a System DSP
When you are dealing with a small PA, say two mains and a sub or two, you can probably get by with the EQ and perhaps output delay that’s in a modern, digital console. Most digital consoles have parametric EQ on the main and matrix outputs, and I’ve been finding lately that if I’m doing more than 4-6 filters on a channel, something else is wrong. Many consoles also have GEQs on the outputs, which would also be handy for trouble spots.
If your subs are in a different timing plane than the mains, you can probably run the outputs through a matrix and put some delay on the outputs as needed. So for simple systems, you can probably get by without a DSP. Certainly if you’re in a small portable setup, not having a DSP will be one fewer thing to schlep in and out each week, one fewer thing to cable and one less thing to deal with.
When we had the flood of ’13 at Coast Hills, we ended up meeting next door in a gym on Sunday. We had our portable JBL Eonsand subs on sticks and I brought my X32 in to mix on. I was able to get a decent tune on the PA with the X32 and everyone was happy with the results. But like I said, it was a simple PA.
I also just put in a small Nexo PS system and used only the DSP in the amp to do all the tuning. Again, it was a simple system; two mains and a sub. Once I dialed in one side to my liking, I copied the EQ to the other side and dealt with the sub on its own.
You Do Need a System DSP
Once the system crosses a few boxes or you get into fills, delays or multiple types of boxes, a system DSP really starts to pay for itself. I’m about to install a L’Acoustics system that will have a main L&R cluster, two side fills, four center flown subs and four front fills. And while it’s true I could do all the timing and processing I need to in the amps, I’m not going to.
With modern matched components, it’s a lot easier to use the DSP in the amp to load the presets which make the speakers sound pretty darn close without anything on them, then use a system DSP to do room correction, timing, and overall tonal shaping. That’s what we’ll do in this case. The L’Acoustics amps will be loaded up with the presets for each type of speaker they’re driving, and a Symetrix Radius will give me delay and overall EQ. I’ll also be doing all my audio routing in the Symetrix. Again, I could do it in the amps, but it’s a lot easier in a dedicated DSP.
You Need Someone Who Knows DSPs
When your PA gets to the size that a dedicated DSP is needed, I recommend you bring in someone who knows what they’re doing to set it up. You can do a lot of damage to your sound and the speakers if you don’t get things dialed in correctly. Things can get complicated quickly and having someone who knows how to properly set things up will save you a lot of grief down the road.
This is perhaps a bit of an over-simplification of the process, but it’s a good starting point.