Audio Interfaces, Sound Cards, and Converters

Choosing the best audio interface for your sound production needs

As digital audio technology became more affordable in the 1990s and early 2000s, a variety of new products enabled music to be made outside of studios without sacrificing sound quality - the most important one being the audio interface. Originally designed simply to convert audio signals from the studio mixing desk to the studio computer and vice versa, they have evolved over time to provide a multitude of connections and solve a variety of problems faced by modern music creators.

Building on the internal soundcards from the likes of Creative Labs and E-Mu, which were utilised in early desktops, early external audio interfaces maximised the advances in new digital connections like Firewire400 and USB 1.1 to enable basic inputs and outputs that allowed musicians and engineers to record anywhere they liked.

Today you can easily find an audio interface that suits your specific needs: rackmountable, desktop or with a satellite controller; 1x preamp or 16x preamps: built-in DSP processing and routing or straight AD/DA conversion; XLR, TRS or minijack outputs. The options are vast so when you’re choosing your next audio interface the biggest question is “Which one best fits my workflow?”

In this article we’ll be helping you navigate the ins and the outs, the digitals and the analogs, the converters and the connections that make up a modern audio interface and what they’ll typically be most useful for.

Analog state of mind - inputs and outputs

Fundamentally audio interfaces allow you to record from external sources and play audio from a computer. How many inputs and outputs are physically provided ranges massively from unit to unit. Most multi-purpose audio interfaces will provide at at least one mic preamp so you can connect a microphone directly to the interface, allowing singers to record themselves wherever they are. Some units will provide up to 8x preamps to allow for more substantial recording setups like drums or remote recording in unconventional spaces.

Some units are still based on the original concept of providing line-level connection between analog devices and a computer. Units like the UA Apollo 16 or the RME M-1620 Pro focus on providing that link without extra bells and whistles and are well suited to studio setups with established workflows that don’t change regularly.

For outputs almost all audio interfaces will provide 2x speaker outputs for you to connect directly to your main stereo speakers/amp, thus allowing you to hear the playback from your computer. Where models differ is what connection that output uses and how many additional outputs it also provides.

XLR and TRS are still the main output connectors of choice and typically depend on the physical size of the unit as to which are used. XLR remains the more expensive and more ‘professional’ choice that typically features on higher-end interfaces but TRS is still very common (just make sure you’ve switched your speakers off before you unplug them from your interface!) Some converters will provide additional outputs for you to connect to alternate destinations, typically an extra pair of speakers for mix referencing, a headphone amplifier box to drive extra pairs of headphones for monitoring, to external processing units like compressors, EQs, reverbs and delays or to feed the inputs of a mixing desk for analog mixing/summing.

These additional outputs are provided individually over either XLR, TRS or RCA connectors, or as a group of 8 channels via Dsub/DB25 connectors to maximise the physical space on the back of the unit.

For headphone monitoring, most multipurpose interfaces will provide at least one dedicated TRS output and some will provide additional outputs (up to 4x) on either TRS or Minijack (3.5mm) sockets.

Digital state of mind - more ins and outs

As the goal of digital audio was to reach the highest possible fidelity, it made sense to create digital-to-digital connections that removed the extra digital-to-analog and analog-to-digital conversions that could introduce artifacts to the audio signal. Several formats were created and are now used in a variety of modern interfaces to connect them to other audio devices - mainly to external preamps, digital speaker inputs, digital mixing desks, etc. The most common digital connections are:

• ADAT - 2x-8x channels delivered via fibre optic cable - typically used to connect to external mic preamps to enable additional inputs for bigger recording sessions/setups.
• S/PDIF - 2x channels delivered via fibre optic cable or RCA cable - typically used to deliver the main mix to external CD Recorders or high-end headphone amplifiers.
• AES - 2x channels delivered by XLR cable - normally used to feed the digital inputs on speakers.
• Wordclock - delivered by BNC coaxial cable - this doesn’t carry audio but enables various digital audio devices to be synchronised together so they can operate as a single system.
• MADI - up to 64x channels delivered via fibre optic cable or coaxial cable - typically used in venues that need to transfer audio over long distances without signal loss issues.
• Ethernet - up to 1024x channels delivered by Cat5/6 cable - Dante (created by Audinate) and Ravenna (often used by Merging Technologies) exploit the AES67 protocol to enable audio to be moved across new, or existing ethernet networks, and is widely used in non-studio locations like music venues, offices and educational facilities.

Many users don’t fully utilise the digital opportunities provided by their interfaces but they can greatly enhance the efficiency and connectivity of any studio setup when implemented correctly. Adding more inputs via external mic preamps can allow a portable 2x analog input interface, like an Audient ID24, to record a whole drum kit. If you want to minimise the number of digital-to-analog conversions when mixing you could choose to connect your audio interface digitally to your speakers via AES, S/PDIF or ADAT and allow the speakers to do the conversion directly.

To USB or to not USB

Audio interfaces have kept pace with the way that we connect devices to computers in a race to stay relevant with emerging technologies. USB 1.1, 2.0, Firewire400, Firewire800 and Thunderbolt have all appeared on the leading interfaces of the day, causing no-end of cable-related-nightmares and delays in recording sessions across the world.

Although there are still audio interfaces that connect via Ethernet cables (Focusrite RedNet range), and more specialised units (like the Atlas from Prism Sound) that connect via HDX to integrate with Avid’s Pro Tools software, the audio industry has mainly aligned behind USB-A and USB-C as the standards for connecting interfaces to computers and the world is a better place for it.

Layers of control

With the increased power of computers and laptops came the greater ability to control a variety of parameters and functions of audio interfaces. Most new interfaces will work as soon as they are plugged into your computer but their respective control software typically allow you to tweak settings to suit your individual setup. You may want to decrease the buffer size to give yourself low-latency monitoring whilst you record, or increase the buffer to give yourself more processing power whilst mixing. You may need to enable additional headphone outputs and what is feeding them. If you have a rackmounted interface away from your desk you may need to use the control software to manage the preamp settings and change gain, filter and pad settings.

Many sound cards now also provide a virtual mixing desk so that you can create a balance of the inputs and outputs and feed that to your speakers or headphones. This allows you to monitor your recording inputs with no or low latency and apply reverbs or delays to make performers hear themselves in a more natural environment. These mixes can often be saved and recalled and are great for engineers or producers working with multiple clients or in multiple studios/recording spaces who want to quickly monitor their projects in a familiar way.

DSP processing

Processors becoming smaller and cheaper brought on a new wave of interfaces that could provide all of the traditional features and connectivity alongside the ability to process and manipulate audio as it’s being recorded. Universal Audio led the way for the industry when they created a way to use their UAD plugins during recordings, and not just during the mixing stage. Companies like Antelope Audio and Steinberg now offer DSP options too which enable the processing to be done in the audio interface, thus freeing up the computer CPU to handle the native plugins or virtual instruments in your DAW.

Interfaces like the Audient ORIA now also provide DSP on individual speaker outputs and work to provide room correction options for immersive audio speaker configurations. The sound of each output can be EQ'd, gained up or down or delayed so it blends with the other speakers to enable seamless movement of sound across the setup.

MIDI

Despite the huge changes that have happened to almost all other aspects of audio interface technology, the humble MIDI connection has kept things simple and remained the same since it was standardised in the early 1980s. The ubiquitous MIDI IN and MIDI OUT 5-pin sockets have been present on almost all of the popular interfaces, placing them at the heart of modern studios - connecting computers, speakers, synthesizers, microphones and more!

Conclusion

All in all there are now hundreds of audio interface options available to suit everyone from the bedroom producer to the biggest concert venues in the world. Some you can put in your pocket and use to record anywhere you like, others will be part of large technical networks that record orchestras or broadcast live to millions of viewers. Improvements in manufacturing and the availability of cheaper microchips has meant that the average quality of an audio interface now is far higher than 20 years ago and music that has only ever gone through a simple audio interface used by bedroom musicians is released to the world on a regular basis.

When the demands of time and quality are at their most demanding, like archiving old recordings or whilst working on live shows or events, we still look to the high-end converters to capture audio at its very best. The digital options available now also mean that it’s easier than ever to keep connected and many speakers, including the HEDD MK20 range, feature AES inputs so your music doesn't get diminished by rogue analog cables or electronic interference in busy studio environments.