When selecting audio interfaces, we’re spoilt for choose these days. There are hundreds to choose from, ranging from cost effective solutions with just one mic preamp and a stereo output all the way up to much more expensive solutions with onboard DSP, high I/O counts and built in monitor controllers.

What you choose of course depends on your budget and requirements for the type of work you do. In this article we’ll cover seven audio interfaces suitable for audio post production. All of the devices in this list incorporate a monitor controller and offer a minimum of 6 output channels for 5.1. Beyond that, the features vary considerably and this reflects the variance in price of the interfaces, with the most expensive coming in at around 14 times the cost of the cheapest.

Frame Edge Sync

One important point to note is that there are several aspects of audio post production which require frame edge sync. Frame edge sync is a method by which the playback of video within a DAW can be synchronised to a video reference signal, guaranteeing that every frame starts at precisely the right moment. The video reference signal, also known as black burst, is essentially a black video signal at the same frame rate as your project. It’s distributed to any video output devices in your system and also to Pro Tools. This requires not only a suitable audio interface but also a Sync peripheral such as the Avid Sync X or the older Sync HD.

The Sync X is capable of generating video reference internally but the Sync HD requires a separate video reference generator connected to its Video Ref In connector. When the system is locked to video reference, the playback of video is precise and no sync drift occurs from one playback to the next. This is important when working on anything where a rock solid lock between audio and video needs to be guaranteed. ADR recording and editing would be a prime candidate for frame edge sync. Not all of the audio interfaces in this list support frame edge sync but it depends on your workflow as to whether or not you actually need it. We’ve included details about frame edge sync within the description for each interface.

Steinberg UR28M (£350)

First introduced back in 2012, the Steinberg UR28M USB audio interface provides two combo mic/instrument/line inputs, two additional line inputs, S/PDIF I/O, two headphone outputs and 6 line outputs. There’s a built in monitor controller with a 3x3 speaker matrix which allows you to use up to 3 sets of stereo monitors, or all 6 line outputs can be used together for 5.1. The two headphone outputs can be fed independent foldback mixes.

The UR28M has some built in DSP effects which include reverb, EQ, dynamics processing and guitar amp modelling. The unit also has a loopback feature, allowing you to mix the input audio signals (line, instrument, mic) with the audio signals playing back from your DAW. This may be useful for live broadcasting via the internet or for anyone making screen capture videos and wishing to combine audio from a DAW with live mic input.

Being the most cost effective audio interface in this list, the Steinberg UR28M is fairly basic as far as post production audio interfaces go but it could be ideal in small project studios where you just need a couple of mic inputs and a simple 5.1 monitor controller. As you might expect at this price point, the unit doesn’t support frame edge sync but if this isn’t a requirement for your work, then the UR28M provides a good value way into surround monitoring.

Universal Audio Apollo x8 (£2400)

This list wouldn’t be complete without the inclusion of an interface from Universal Audio. In fact, this is the first of two. The Apollo x8 is ideal if you need a thunderbolt interface with surround monitoring up to 7.1 but don’t require Dolby Atmos capability. 8 channels of line in/out are provided on 1/4” jacks and there’s S/PDIF I/O too.

The x8 includes 4 Unison-enabled mic/line preamps, giving you fully authentic preamp emulations from Neve, API, Manley, Avalon and others.

Universal Audio include their Realtime Analog Classic Plus plug-in bundle. This includes emulations of analog compressors such as the Fairchild 670 and Teletronic LA-2A and EQs like the Pultec EQP-1A. The x8 features six DSP chips and 50% more processing power than previous Apollos so that’s good news if you want to run plug-ins at near zero latency regardless of audio buffer size.

Frame Edge sync is not supported on the Apollo x8.

As with all Apollo interfaces, the x8 provides convertors with a wide dynamic range and ultra-low noise.

Metric Halo LIO-8 mkIV (£2750)

Now in its 4th generation, the LIO-8 from Metric Halo is a hugely capable audio interface which offers extremely high quality converters and low round trip latency. The unit can be connected to your computer via USB-C or through Metric Halo’s proprietary MHLink gigabit ethernet technology.

The LIO-8 mkIV includes a custom DSP/FPGA processing system which provides massive amounts of processing and memory for high-precision fixed point mixing, cross-point interpolation, metering and routing as well as floating point plug-in processing. An integrated tracking DAW called Session is included, along with over 100 zero latency plug-ins to run on it.

One of the things which makes the LIO-8 mkIV so enticing for post production work is the multi-source, multi-destination monitor controller which is surround capable up to Dolby Atmos 7.1.4. The interface includes 8 channels of analogue and 8 channels of AES I/O simultaneously but you can also install an Edge Card which allows you to add digital I/O to the interface. If you need to expand the system further, multiple Metric Halo interfaces can be linked together using MHLink for a maximum of 128 channels at 32-bit, 192kHz. Monitor controllers can be set up in software, mixing and matching between digital and analog outputs for any number of units.

The LIO-8 mkIV is power efficient, consuming 25 watts of power when phantom power is active on every mic channel. Without phantom power it uses less than 21 watts. The low power consumption means that the unit runs cool and so no fans are needed, making it silent in operation.

The unit includes SMPTE LTC I/O, MIDI I/O and Wordclock I/O. 

One thing which the Metric Halo LIO-8 is not capable of is frame edge sync since this requires a Digilink connector in order to be able to integrate an audio interface into a Pro Tools HDX or HD Native system running a Sync HD or Sync X (see the Focusrite Red16 Line description below for more details on frame edge sync). If you don’t need frame edge sync though, the Metric Halo LIO-8 mkIV is a superb mid-tier audio interface which many post professionals rely on for their day to day work.

Universal Audio Apollo x16 (£3200)

The Apollo x16 is Universal Audio’s flagship thunderbolt audio interface. 16 channels of line in/out are provided on D-subs and there’s AES/EBU I/O too.

The unit does not include any mic preamps but up to 4 thunderbolt equipped Apollos can be combined together for expanded I/O and controlled from your desktop using Apollo Twin or x4.

As with the x8, the Realtime Analog Classic Plus plug-in bundle is also included with the Apollo x16. Again, there are six DSP chips which allow you to run plug-ins at near zero latency.

The Apollo x16 is an all-in-one monitoring hub for mixing formats up to 9.1.6. This makes it suitable for Dolby Atmos, Auro-3D, Sony Reality Audio and others. The front panel monitoring functions include Alt Speakers, Talkback mic and assignable dim or mono.

Both the Apollo x16 and Apollo x8 offer selectable +24dBu operation out of the box, providing compatibility with a range of pro audio equipment.

Frame Edge sync is not supported, so if this is a deal breaker the you might want to consider the Focusrite Red16 Line which is slightly more expensive but includes Digilink connectors. The Apollo x16 does include Wordclock I/O for synchronisation with other devices.

The quality of A-D/D-A conversion is excellent and the x16 boasts the widest dynamic range (133dB) and lowest THD+N (-129dB) of any integrated audio interface on the market. Sample rates up to 192kHz are supported.

Focusrite Red16 Line (£3500)

We’ve mentioned frame edge sync a couple of times now and the Focusrite Red16 Line is the first interface in this list to provide this feature. Assuming that you already have a Sync HD receiving video reference, or a Sync X generating it internally, there are a few other things you’ll need for frame edge sync. Firstly, the sync peripheral has to be connected to your HD Native or HDX card with a serial cable. Secondly, since the sync device has to act as the master clock in order for frame edge sync to work, there has to be a clock signal sent to all devices in the system. This can be done either through Loop Sync or Wordclock. Finally, you’ll need interfaces with Digilink connectors so they can form part of the HD Native or HDX system. The Focusrite Red16 Line provides loop sync and Digilink, making it an ideal alternative to Avid’s own audio interfaces whilst still providing the frame edge sync functionality. The Red16 Line also includes two thunderbolt 3 ports for use outside of the HD Native/HDX architecture.

The Red16 Line is a 64-in/64-out interface with ultra-low latency A-D/D-A conversion, two digitally controlled Red Evolution mic preamps with up to 63dB of ultra-clean gain, stereo linking, individual phantom power, high-pass filter and phase reverse. The preamps provide a dynamic range of 121dB.

If you use Pro Tools along with a second DAW, the Red16 Line allows easy switching between Digilink and Thunderbolt by changing the host mode in the included RedNet control software. The software has extensive options for setting up monitoring and routing configurations and remote control of mic preamps. In terms of I/O, there are 16 line inputs on D-sub coupled with 16 line outputs and two main monitor outputs. Added to this, there’s also dual port Dante connectivity providing a means of expanding your studio over ethernet at low latency and reasonable cost.

Other features include three LCD displays for accurate level metering, two discrete headphone outputs, two instrument inputs on the front panel and an ‘Air mode’ on the preamps, designed to give recordings the clarity of a transformer based ISA.

With all of the features on offer, it’s easy to see why the Focusrite Red16 Line has been adopted by so many post production facilities already. It provides the outputs and monitoring necessary for Dolby Atmos and retails for a notably lower price than Avid’s MTRX Studio interface. As with all of Focusrite’s Red interfaces, the Red16 Line gives you the option to add a RedNet R1 desktop remote controller for convenient control of monitoring and source selection, meaning you can keep the interfaces in your rack and keep your desktop free of clutter.

DAD AX Center ($4000)

A few weeks ago, Digital Audio Denmark announced the release of AX Center, a premium modular audio interface that includes monitor control and 128 channels of speaker processing with a total of 1024 filters and delays. It’s compatible with a range of DAD’s expansion cards, including the SPQ speaker processing card which can be configured to various different filter characteristics and channel layouts via the DADman control software and is all integrated and easily managed by the PRO|MON monitor control section in DADman.

While the back panel on The AX Center appears quite simple, this belies the true I/O capabilities of the unit. The thunderbolt 3 connectors both provide 15 watts of power and can handle 256 bidirectional channels at 48 & 96kHZ, 128 channels at 192kHz ands 64 channels at 384kHz. Each port can act as a main or expansion port. There’s also Dante with 256 bidirectional channels at 48kHz and 96kHz and 128 channels at 192kHz. MADI is included too, with the BNC connectors providing 64 bidirectional channels at 48kHz, 32 channels at 96kHz, 16 channels at 192kHz and 8 channels at 384kHz. Finally, there are dual ADAT interfaces on TosLink connectors.

The unit is expandable via the two DAD I/O expansion slots and through the module slot for optional dual MADI modules via 2xSFP connectors.

For synchronisation, Word Clock I/O and video black burst inputs are provided on BNC’s. DAD AX Center does not have a DigiLink connection therefore it cannot support frame edge sync.

The summing processor in the DAD AX Center provides 64 outputs and 512 busses and the internal router is 4096x4096.

The DAD AX Center has only just been released but the extensive I/O capabilities coupled with speaker processing and compatibility with Dolby Atmos output configurations make this a very serious interface which should fit well into many post production studio systems.

Avid Pro Tools MTRX Studio (£4800)

If you’re working with Pro Tools Ultimate and want to stay with the Avid ecosystem then the Pro Tools MTRX Studio could be the ideal choice of audio interface. With 64 channels of Dante I/O, 16 channels of ADAT I/O, 16 line inputs on D-Sub, two mic inputs with premium preamps, 16 line outputs on D-Sub and a pair of stereo monitor outputs on 1/4” jacks, the Pro Tools MTRX Studio offers all of the connectivity that most users will need. Dual headphone outputs are also included.

A-D and D-A conversion is courtesy of Digital Audio Denmark, providing the same pristine audio quality found on DAD’s own interfaces. The MTRX Studio supports all Pro Tools sample rates from 44.1kHz to 192kHz.

MTRX Studio is EUCON-enabled and delivers tight integration with Pro Tools Ultimate, enabling you to control all audio sources, monitoring and routing directly from any Avid control surface.

Speaker calibration is built into the MTRX Studio. In fact, it’s the same SPQ speaker processing technology which is available as an option for the more expensive Pro Tools MTRX. Different monitor profiles can be created from mono up to immersive. Dolby Atmos 7.1.4 and larger setups are supported. All routing and speaker calibration is done via DADman software. The 512x512 matrix allows you to route any MTRX Studio input to any output. Audio can be sent to multiple devices simultaneously and cue mixes can be sent over Dante.

Of course, the MTRX Studio connects to a Pro Tools HD Native or HDX system via Digilink and includes Wordclock and Loop Sync I/O. Frame edge sync is supported.

Final Thoughts

Audio interface requirements for audio post can be very specific. When deciding on which one to buy, you should consider your current needs along with potential future requirements and expandability options. I/O and monitoring capability are of course two of the most important factors along with the cost. The list of interfaces in this article is intended to cover a variety of price points and technical requirements. It’s certainly not an exhaustive list and there are many other interfaces available which would be suitable for post production work but we’ve attempted to highlight some of the most notable options.

As usual, we’re interested to know your thoughts on this. Are there any key brands we’ve missed out? Let us know in the comments what your preferred audio interfaces for audio post are.