Tuesday VO Tech Tip: Virtual Routing Revisited

To their credit, most commonly recommended audio interfaces quickly find their place in the home VO studio. That red, blue, or grey box connecting microphone to computer just sits quietly on our desks, reliably handling the tasks of digitization and amplification. Most of the current models work well every day with no fuss or muss.

Yet, audio interfaces are also slightly awkward pieces of gear, simplifying tasks that used to be handled by complex mixers. While interfaces effortlessly handle the basics, they may not quite achieve unique tasks a voiceover studio needs.

One VO session challenge is the “need” to play back audio we’ve recorded. On most interfaces, audio playback is only heard locally, and some voice actors have resorted to clumsy hacks such as holding their headphones up to their microphone so a director on the other end of the connection can hear the recording.

How audio “Loopback” gets implemented in an audio interface

Although many interface manufacturers claim they provide “Loopback”, the term is used differently by different companies. In many cases “Loopback” will only provide audio into another recording application, rather than send it “down the line” to a remote director. With some devices, this type of Loopback simply doesn’t do what a home voiceover studio needs it to achieve.

However, routing audio within and between applications is tricky stuff, and there may be some happy accidents. This occurred for me while using my Focusrite Scarlett 2i2 Gen4. Focusrite had recently updated their Control 2 software (which allows a computer to change settings in real time on the hardware interface when it’s connected). In addition to adding some accessibility features, the update now allows the creation of presets for gain, mixing, “Clip Safe”, and routing settings. That creates a “scene” or “snapshot” of each setup you may have, allowing you to save them to your computer and recall them later. It’s a powerful addition to a solid interface.

Focusrite Scarlett 2i2 Generation 4 Loopback

The new version also enables Direct Monitoring audio to be sent to “Loopback”. This adds two virtual channels to the interface, similar to how SSL implemented it to their SSL2/2+ models last year. Channels 1 and 2 are the regular microphone connections, while 3 and 4 are these new virtual audio sends. At first glance, this “inter-app” Loopback did not seem to be much of a change. An unintentional playback from my MacOS during a session showed how this can work to our benefit depending upon how our director is connected.

I had been working with a client over Zoom and pressed “Play” on an audio file. The client said “That sounds good!” I had not been sharing my screen or audio through Zoom, so they should not have been able to hear the audio i was playing. Experimenting further, I found that when I turned off the “Send Direct Monitor mix to Loopback” option in the Control 2 software, they could not hear the playback. This meant that Zoom was “hearing” all of the channels being sent by the Scarlett. Zoom also received input from my microphone so I was still able to communicate with the client without having to switch inputs.

Another Loopback variable – the communication software

This ability seems to be directly related to the audio capabilities of Zoom. The “Microphone” choices in Zoom do not show separate inputs on MacOS. Everything is aggregated under “Scarlett 2i2 Gen4”. But it is clearly passing through audio which it receives from the additional channels.

The SSL2+ worked the same way when I tested it – both sending audio out to Zoom without the need to “share” the audio or screen as a separate step. This differed from the tests I did last year when the functionality was first added to the SSL.

This change points to the other big variable in any kind of virtual routing: the way a specific app handles audio input channels “under the hood”. When I tested this with Google Meet the Loopback channels (3 & 4) did not go through to the person on the other end of the line. Since Meet is browser-based rather than a standalone app, this seems to be a limitation of the Chrome browser to “hear” the additional audio channels.

Source-Connect shows input details

Afterward, I opened Source-Connect Standard 3.9, which allows me to choose individual inputs in a mono session – the Scarlett appears with 4 discrete inputs as shown in the screen grab below. That let me determine what was actually going out on each channel. The Scarlett channels 1 and 2 sent only the microphone input, but 3 and 4 sent any playback from the recording software and the attached microphone. That was consistent with the way Focusrite describes the new feature – “Send Direct Monitor to Loopback” would include everything I hear through my headphones. Attaching the SSL2+, I found similar behavior, except that it did not appear to send the microphone input out on Channels 3 and 4.

As I’ve said before, keeping track of “virtual” audio routing can be a bit brain-bending. I’m going to keep playing with this, as one of the variables will continue to be the software we are connecting with.

Have you tested your studio’s audio quality to make sure it meets professional standards? For a free review of your vocal recordings, please use the upload tool on my Audio Review page.

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