/ audio

DSP all the Wedges

The band’s PA is run through a dbx driverack, and I must say it’s a pretty slick setup. I like having the processing chain in one unit, and it’s mostly set-and-forget when you get to the venue. It got me thinking about the monitor mixes – how can I approach them in the same way?

A 31-band, 1/3 octave EQ is generally considered essential equipment for monitor mixes. But what about automatic feedback suppression? It’s arguably more necessary for foldback than it is for front-of-house. Maybe you want to filter out below 100 Hz and above 12 kHz, as those frequencies aren’t terribly useful for live monitoring. Limiting, for protecting expensive wedges? I wouldn’t say it’s high on the priority list, but it would be nice to have.

So after a little research and a very fortuitous win on some type of auction website, I found myself the proud new owner of a dbx Driverack 220i. It’s a unit intended for commercial installation (as evidenced by the titular “i”) but I believe it could work rather well in monitor world. Similar to the driverack PA+ model that’s running the mains, the 220i provides selectable blocks of DSP processing including parametric EQ, graphic EQ, high- and low-pass filters, feedback suppression, and limiting. This sounds exactly what I need to “set-and-forget” the monitor mixes.

It may seem like a disadvantage at first glance, as this particular unit has very few front panel controls. Essentially you can only change presets from the front panel, so all configuration is done from a rather dated Windows-only utility. However in practice, I think this might actually be an advantage especially if you run the bar circuit where you can’t ring out monitors and you don’t have the extra time anyway. Or for a band running their own sound, perhaps on occasion you have less-knowledgable people setting up and running the rig. Having two monitor mixes ready to go by literally just patching it in would be pretty great.

I have my unit configured for two separate monitor mixes. Each channel has its own high- and low-pass filters, EQ, feedback suppression, and limiting. In theory the filters and EQ have tailored the frequency response for a decent mix using my specific wedges, the limiter is set to protect the drivers, and the automatic feedback suppression is set to “live” mode so it will automatically notch out feedback during the gig. I even have multiple presets that I can change from the front panel depending on what kind of mix I need. I have a “flat” mix that evens out the response of my wedges so it will sound natural. I also have a preset with pronounced midrange which is key for cutting through a loud stage. This is the “set-and-forget” part; I can pick a preset at the beginning of the night or even switch between acts, and there should be nothing to operate during the show.

But what if there is? Most of the time I think this setup will be very autonomous, and will be quite successful. But you have to be prepared to change something on the fly, and in that event you would need a laptop and a serial cable to tweak anything. If you’re not already bringing a computer to your gig, this would be very cumbersome. Something I am bringing to every gig, however, is a smartphone. Sometimes even a tablet.

Dbx provides a mobile app for the PA2 model which looks very nice, but none of the older models in the lineup made the cut. What the 220i does have is a good ol’ RS232 port. What I envision is attaching the driverack to a TCP/IP network using a serial terminal server, and sending commands via an app on the phone or tablet. This requires knowledge of the control protocol that the official utility uses to configure the driverack, so to that end I will be documenting any information I’ve gathered on the control protocol here.