Technology: Interfacing audio with computers
Technology: Interfacing audio with computers
With so many different audio interfaces available to choose from, it’s important to know how they differ
When you think of audio recording, your brain quite possibly conjures up images of long reels of tape alongside a mixing console adorned with hundreds of knobs and wires poking out of it. But this is rarely how audio recording happens in 2019. Of course, there is no shortage of analogue enthusiasts still championing such technology but, as with many things in this world, a whole room worth of equipment has been replaced by a little box, aka the computer.
Digital recordings were already happening on magnetic tape before the computer took over thanks to technology like ADAT; however, recording to a computer provides so many benefits over linear formats like magnetic tape that it’s no surprise that almost all non-location modern audio recordings today are made with a DAW – a digital audio workstation, namely a computer running audio editing and recording software. Furthermore, the expectation among your congregation that your ministry is recording and archiving its services and events is only growing with time. But, in order to feed audio into a computer, you will first need an audio interface.
Audio interface – what is it and why do you need one?
An audio interface is, in essence, an analogue-to-digital signal converter with lots of bells and whistles attached tailored specially towards audio recordings. Technically speaking, a computer sound card is an audio interface. It is capable of sending audio signals to your computer in a format the computer can recognise. The chances are high that by using this sound card your computer sports audio inputs and outputs (3.5mm headphone and mic ports) straight out of the box, so won't that be enough?
Most standard sound cards are fairly basic in their connectivity options, offering solely what’s required to get consumer-level sound into the computer. This typically means a stereo line input (or two if you’re lucky) for connecting a computer microphone, along with a headphone output and stereo line output for speakers. Even if all that’s required is simple recordings of vocals and a guitar, a sound card lacks the appropriate connections. A proper microphone will sport an XLR-balanced audio connector, while the guitar requires a high-impedance line input to match the signals generated by its passive pickups and ensure that the resulting sound inside the computer won’t be significantly affected. As such, the term audio interface, when uttered by anyone in our industry, typically means ‘a professional audio interface’. Ease-of-use and high-quality audio capture are the differentiators between such devices. Audio interfaces come in all shapes and sizes and feature built-in microphone preamps, which amplify your mic's signal to line level. This is a step up in volume from what the mic can produce on its own, and can be read by a computer. The very first thing you need to decide on before selecting an audio interface is the input/output connectivity required for recording and playback.
How does an audio interface affect sound quality?
Nowadays, great quality audio recordings can be achieved by reasonably priced interfaces, yet there is still a big difference between solutions at each end of the market. This is largely down to the quality of the analogue/digital converter and preamp used inside the device. The converter is responsible for converting the analogue electrical signal generated by a microphone or instrument pickup into a ‘ones and zeros’ digital signal. The preamp’s job is then to take that very weak digital signal and amplify it to useable levels. More expensive audio interfaces typically use better-quality preamps and converters intended to colour the audio as little as possible (or colour it in a way that is desirable to the ear). The most hotly quoted specifications for audio quality in interfaces are typically dynamic range and signal-to-noise ratio.
While buying an interface with the lowest-possible background noise is sensible, in the real world many musicians won't be able to hear any difference at normal listening levels. If you're capturing a live performance via a mic, the background noise level of that mic and its preamp may already be higher than that of the audio interface, especially since it's difficult to make recording areas really quiet without extensive soundproofing. Other specs to understand and be aware of include the bit depth, sample rate and frequency response. Many budget interfaces now sport 192kHz sample rates, making this spec increasingly less important. Bit depth is the number of bits captured in each sample per second. As this changes, so does the dynamic range, which is the difference between the lowest and highest volume of a signal that can be recorded. Jitter is another aspect that can affect audio quality but is rarely stated by manufacturers.
Choosing the right connectivity
Connectivity of the interface then comes in two forms. Audio – the inputs and outputs responsible for handling the transfer of audio through the device; and data – how the device itself ‘talks’ to the computer. The very first thing you need to decide on before selecting an audio interface is the input/output connectivity required for recording.
If you’re a singer-songwriter who wants to capture your voice and acoustic guitar using microphones, a pair of balanced mic inputs may be all that’s needed. If either of these mics is a condenser type though, you’ll need an input with phantom power to power it. If you’re going to be playing an electric bass, guitar or electronic keyboard that you want to connect directly to your recording setup, you’ll need an instrument-level input, also known as a high-Z input. To connect external gear such as drum machines, samplers and external sound processors such as effects units, you’ll need line-level inputs and outputs. Many studio monitors and headphone amps that provide a separate headphone mix to performers also require line-level I/O. For very simple speech recordings, a USB mic could be sufficient. Such units are essentially a microphone and audio interface built into a single package that can be connected directly to the computer (usually via USB).
If, for example, you intend to record a full band setup, you’ll likely need an interface with at least 8–16 physical XLR/TRS inputs. A full-scale mixer with an audio interface built in may well be the better option in such scenarios. Mixers have equalisers and volume faders for each individual input channel, giving you maximum control over every sound that goes into your computer. You'll also often get on-board effects such as reverb, delay and chorus that you can apply to individual tracks.
A major advantage of a mixer over a simple interface is therefore its usefulness managing live performances. The increased input and output options make them ideal for assembling multiple instruments played simultaneously into a coherent mix. Perhaps your church also already possesses and uses an analogue mixer for mixing its weekly services, but would now like to archive those services as well. All you would need is a fairly basic audio interface to expand your system and turn the analogue signals to digital.
Why would you pick a basic interface over a fully functional mixer if cost is no issue? Typically, space and portability. Users mixing and producing inside a DAW already have access to virtual faders, auxes, busses and effects provided by the software, yet managing all these in a live situation with multiple sources can be challenging via just a keyboard and mouse.
Finally, there are also different connectively options available for connecting your interface to your computer, with the most common being USB, Firewire, Thunderbolt or PCIe. While most interfaces work with both Macs and PCs, there are a few that have specific Mac or PC compatibility to be aware of. The majority of popular interfaces are USB, thanks to the fact that almost every modern computer sports a USB port. While typically more expensive, Thunderbolt interfaces offer high data bandwidth and low latency, allowing them to handle many simultaneous inputs and outputs.
As you hopefully can see from the points above, there is no such thing as a ‘best’ audio interface – it all depends on your application and requirements – but there are plenty of differentiators to be aware of prior to purchasing. Understand what it is that you’re trying to achieve before working back through the amount of input and outputs you’ll need, then decide the most appropriate format for connecting to your computer, before finally settling on a set of audio specifications that are good enough for the job at hand without going overboard and breaking the bank.
This article first appeared in the July-August 2019 edition of Worship AVL. Subscribe at www.proavl-central.com/subscribe/worship.