Recording Gear: Audio Interfaces in the VO Studio – The Basics

When I finished the 6-Part Series on VO Microphones, the next three emails I received all asked about “the best audio interface” for a voiceover mic. A couple more voice actors wondered whether any of the recommended XLR microphones needed a special preamp. Another asked how interfaces were different than “sound cards.” As with any audio equipment, we can descend into a deep rabbit hole of various models and features. But for most of what we do in VO, the audio interface can be pretty simple.

Definitions: Sound Card v. Preamp v. Mic Pre

First, a definition: you may hear people refer to “Sound Cards” or “Preamps” or “Mic Pre’s”. If they are referring to the device that sits at the end of your XLR cable and connects to your computer via a USB cable, then they are talking about audio interfaces.

Sound Cards are dedicated circuit boards that plug directly into a slot inside of your computer. This type of hardware harkens to the days when it was more common to remove the case from your computer and directly install specialty hardware to give it more functionality. These days, we just connect a self-contained external device through a high speed data cable, such as USB. The benefit is that we no longer have to worry about whether upgrading our computer makes our plug-in cards obsolete.

Preamps or Mic Pre’s are kind of describing the same thing – an amplifier which takes the relatively low output from a microphone and boosts it up to a level that is useful when recording.

What is an Audio Interface?

An Audio Interface does what a Sound Card used to do – first amplify and then convert the incoming analog signal into 1’s and 0’s that the computer can deal with. Because they are external, self-contained devices, they just need to follow the easier guidelines of data transfer rather than how to connect to a computer motherboard. That keeps things simple for us.

These days, most audio devices are “Class Compliant” – meaning that in many cases (particularly on the MacOS side of things) you won’t need to worry about separate “driver” software. They are just plug-and-play.

What Actually Influences Our Audio Quality?

Honestly, I tend not to worry too much about this part of the input chain, preferring to keep things simple. In almost every case, the quality of our audio recordings are much more highly influenced by three other factors:

1. The source (the timbre and volume of your voice)
2. The room (which will act upon the sound in fairly complex ways)
3. The microphone (remember, microphones are basically filters)

Current Audio Interfaces are seldom the bottleneck to high quality audio.

But – what does an Audio Interface actually do?

As I mentioned above, an Audio Interface receives analog (voltage) input from the microphone through the XLR cable. A preamp circuit amplifies that input (typically +40-60 dB of gain – which means that they are designed to handle the input from a condenser microphone). The interface’s converter chips analyze the voltage and change it into digital information for the computer. This information travels down the data cable (commonly a USB or USB-C cable) where your recording software records it and renders cool waveforms to your screen.

Many interfaces provide a “Direct Monitor” option, so you can hear the audio as it comes into the interface, before it is digitized. That way, you can hear yourself with no time delay. Sometimes the controls for Direct Monitoring are (1) a switch on the device, (2) a “Mix” knob which balances between the audio coming back from the computer and the input from the microphone, or (3) a software control panel where you might set those things through your computer.

The Audio Interface also handles conversion during playback. It makes sense of the digital data from the computer, converts that back into a voltage signal which goes into our headphones or speakers. This audio output uses the high quality converters and amps in the interface, and often sounds better than the audio coming out of the headphone port on your computer.

All of audio input generally occurs with very little change to the signal. What we end up with is an accurate transfer of our voice through the microphone and into the recording software.

NEXT –
Why we might want an Audio Interface to actually “distort” the signal a little…or at least be aware of how that happens.

This information recently went out directly to my email community.
If you would like to join in to receive those emails the day they publish, please take a moment to share your contact information through this sign up form.
Thank you.