Easy ASIO Interface Expansion for More Inputs

Easy ASIO Interface Expansion for More Inputs

No, you usually can’t run two ASIO interfaces in the same system. But we have ways...

by Craig Anderton

No matter how many inputs you have, sometimes it’s just never enough. Because most of my work is solo, you’d think I need only a few inputs at a time, but I prefer to have interfaces with enough inputs that I don’t have to re-patch, and can leave instruments set up for inspiration at a moment’s notice.

For example my main interface is the USB 3.0-compatible TASCAM US-20x20, with 8 front panel mic/line inputs and two line ins on the back. The first four ins are guitar, bass, and two Line 6 Helix outputs. The next set of four inputs use phantom power for two Neat Worker Bee mics, one Neat King Bee, and one Audio-Technica AT3035. The outs from a Korg M3 go into the two line ins...so I’m covered, right? Well, except for the M3’s four individual outputs, the individual outs from my SP-1200, various and sundry other synths, feeding in the output from samples recorded on my iPhone or TASCAM DR-22WL, and...I need more inputs.

Macs can aggregate interfaces; Windows can with its native drivers, but most of us use ASIO for its low latency and high performance with streaming audio. Although some ASIO interfaces can be aggregated with Windows, that’s the exception rather than the rule. Fortunately, there’s an easy way to add more inputs if your interface has an ADAT optical input: pair it with a device that has an ADAT optical output.

HOW IT WORKS: A REPRESENTATIVE EXAMPLE

Let’s use the US-20x20 as an expander module for other interfaces (of course it can also expand itself, but the sub-$500 price and excellent mic pres make it a good candidate for expanding other devices). Also, the US-20x20 was designed specifically to do this as well as serve as an audio interface, because it has an ADAT optical output, and the option to switch it into a Mic Pre mode. This means it no longer needs to connect to your computer via USB, and the eight mic inputs feed both the analog and ADAT outputs simultaneously.

This shows the TASCAM US-20x20's routing when set to Mic Pre mode. Note how the mic preamp outputs go to both analog and ADAT digital outputs.

Furthermore, you can control gain directly from the front panel, and don’t need to set up any routing from an applet or mess with any software. Let’s expand a Zoom UAC-8 audio interface, and assume a mic plugs into Input 5 on the TASCAM.

1. Set the TASCAM’s Mode to Mic Pre.

2. Patch a TOS Link optical cable from the US-20x20’s ADAT out to the UAC-8’s ADAT in. You can buy these cables pretty much anywhere; I bought one at Target.

3. Open up the UAC-8’s mixer application, and (important!) choose ADAT as the sync source.

4. If you sing into a mic plugged into the US-20x20, the UAC-8’s mixer application will show it in the corresponding channel. For example in this case, Input 5’s meter shows it’s receiving signal.

Here, the UAC-8's mixer application is set for the proper sync (ADAT). The mic signal from the TASCAM interface is showing up in the Zoom's ADAT channel 5.

5. The UAC-8’s ADAT inputs will appear as input options in your DAW. Select the input as you normally would to record the mic into a track.

I think SONAR has enough inputs now...

6. For zero-latency monitoring, turn up the monitor for ADAT 5 in the UAC-8 mixer. To monitor through the computer and hear any effects you’ve inserted into a track, turn down the UAC-8 mixer’s fader, and choose input echo in your DAW.

And that’s pretty much all you need to do.

BUT WAIT, THERE’S MORE!

Isn’t there always...here are a few fine points.

• The ADAT optical connection carries 8 channels only at 44.1 and 48 kHz sampling rates. At higher sampling rates, the channel count goes down (4 channels at 96 kHz, and 2 channels at 192 kHz). Note that not all devices can send and/or receive ADAT signals at higher sample rates, although it’s fairly commonplace.
• The signals carried over ADAT are digital, so there’s none of the audio degradation you might get by using an analog sub-mixer. The signal appearing at your DAW from the expansion mic preamp is no different from the one coming from your interface.
• The expansion interface doesn’t have to be next to your main interface; the length is limited only by the optical cable. The ADAT spec assumes a maximum length of about 16 feet, but with high-quality optical cables, you can go much further. So you could have, for example, the "expander" next to a keyboard rack, and not have to run a zillion cables from your keyboard to the main interface.
• There are dedicated mic preamps with ADAT outputs, but an interface often has more functionality, like also being able to serve as a digital mixer.

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 Craig Anderton is Editorial Director of Harmony Central. He has played on, mixed, or produced over 20 major label releases (as well as mastered over a hundred tracks for various musicians), and written over a thousand articles for magazines like Guitar Player, Keyboard, Sound on Sound (UK), and Sound + Recording (Germany). He has also lectured on technology and the arts in 38 states, 10 countries, and three languages.