PreSonus Blog

Add More Inputs to Your Audio Interface


I never liked patch bays. I certainly didn’t like wiring them, and I didn’t like having to interrupt my creative flow to patch various connections. In my perfect world, everything would patch to its own input and be ready to go, so that you never had to re-patch anything—just assign a track to an input, and hit record.

With enough audio interface inputs, you can do that. But many audio interfaces seem to default to 8 line/mic ins. This makes it easy to run out of inputs, especially as synth fanatics gravitate toward re-introducing hardware to their setups (and want to take advantage of Studio One 5’s Aux Channels). We’ll assume you don’t actually want to get rid of your interface with 8 mic/line ins…you just want more. There are three main solutions:

  • Use a mixer with audio interfacing capabilities. A StudioLive will certainly do the job, but it could be overkill for a home studio, unless it’s also what you use for gigs.
  • Aggregate interfaces. We’re getting closer—simply add another interface to work alongside your existing one. It’s easy to aggregate interfaces on the Mac using Core Audio, but with Windows, ASIO almost never works for this. So, you need to use Windows’ native drivers. The newer WASAPI drivers have latency that’s close to Core Audio, but aren’t widely supported. So, you may be stuck with the older (slooooow) drivers. Another issue is needing to give up another USB port for the second interface, and besides, using different applets to control different interfaces can be a hassle.
  • ADAT optical interface. This is my preferred solution, which works with both Mac and Windows. It’s especially appropriate if you record at 44.1 or 48 kHz, because then you can add another 8 inputs per ADAT optical port. (At 88.2 or 96 kHz, you’re limited to 4 channels per port, and not all audio interfaces are compatible with higher sample rates for optical audio.)

Why ADAT Optical Is Cool

I started with a PreSonus Studio 192 interface, graduated to a PreSonus 1824c, but kept the Studio 192 as an analog input expander. The 192 has two ADAT optical ports, so it can send/receive 16 channels at 44.1 or 48 kHz over a digital audio “light pipe” connection. The 1824c has one ADAT port for input and one for output, so patching one of the Studio 192’s optical outs to the 1824c’s optical in gave a total of 16 analog inputs. This accommodates my gear without having to re-patch.

Another advantage is that the Studio 192 has +48V available for individual mic inputs, whereas the 1824c’s +48V option is global for all inputs. So, I can easily use a mix of ribbon, dynamic, and condenser mics with the 192, while leaving +48V off for the 1824c.

The interface being used as an “expander” doesn’t require a permanent USB connection to your computer (although you may need a temporary connection to change the interface’s default settings, if you can’t do that from the front panel). And, you don’t need an interface with lots of bells and whistles—just 8 inputs, and an ADAT out. A quick look at the used market shows plenty of ways to add another 8 channels to your audio interface for a few hundred dollars, although this could also be a good reason to upgrade to a better interface, and use the older one as an expander.

Because the 1824c has an ADAT input, both interfaces show up in the Song Setup menu. The inputs from the ADAT light pipe look, act, and are assigned like any other inputs (Fig. 1).

Figure 1: It even kind of looks like a patch bay, but I never have to patch any physical connections.

Time for a Caution…

…and that caution involves timing. Always set the ADAT expander as the master clock, so that it’s transmitting clock signals to the main interface, which is set to receive the clock (Fig. 2). If the main interface is the master, then the expander will be free-running and unsynchronized. The audio will seem to work, but you’ll get occasional pops and clicks when the units drift out of sync (which they will do over time).

Figure 2: Make sure the main interface syncs to the expander’s clock.

Patch bays? Who needs ’em? I like virtual patch bays a lot more.