All-pass filters can be a very helpful tool to get two speakers to work together, especially when they are from different families or brands. Unfortunately, they are normally only available on higher end output processors and amps like Meyer Sound Galileo, Lap Gruppen PLM series, or Lake.

There is a free solution, though, which I’ll be testing out in this post.

The Setup

After my interview with Michael Curtis I’ve been looking at Reaper more and more. For these tests I’ll use the ReaEQ that comes with it.

Although Reaper isn’t technically free, it does come with a 60-day evaluation license. I did do some research into other available VST plugin hosts, but haven’t tested them, yet, so I’ll save that for another post.

A few years ago I published a video called The Poor Man’s Galileo. You can see that I’ve been interested in replacing various parts of my hardware setup with software for years. I wish I was a flute player. I love gear, but I hate how heavy and bulky it all gets. I love tools, but it’s hard to justify carrying them everywhere if I I’m not that I’ll actually need them. I always have my computer, though, which makes the software solution attractive.

I set up two computers with Reaper. One to host the plugin and proces the audio and the other to record. I created two record channels. One that was a simple loop from out to in so that it would experience the same A to D process, effectively removing it from the measurement. The other went to the OCTA-CAPTURE for live processing.

I ran a sine tone for verification and discovered that there was no block size too low. With only the ReaEQ inserted I was unable to interrupt processing with any errors. Once I dropped below 29 samples, though, Reaper stopped reporting a lower latency. In a later test, when I tried inserting an Ozone 9, I had to bring the block size back up to 32 to perform without any audible hiccups.

Latency

The main thing I wanted to confirm here is that the latency would be low enough for live use. How low is low enough? That depends on everything else in the system and the application. For an IEM monitor rig, 20ms might be too much after other possible latencies in the system, but probably wouldn’t make that much different for a big outdoor gig.

I guess the big question is whether the benefit is worth the expense. If you making a big improvement to a two octave wide crossover region and the latency seems acceptable, it’s probably worth it.

With no plugins inserted I measured a round trip latency of 5ms for my test setup. It stayed the same after inserting the ReaEQ. Just to confirm that I would see a change, I tried inserting an Ozone 9 with 3 modules and the latency jumped up to 75ms.

Conclusion: I would be happy to use this setup as a backup solution in the field. If there’s an internet connection or cellular data connection, I can get Reaper installed on any machine in a few minutes.

Have you tried live processing with plugins system calibration in the field? Let me know in the comments below.