The audio interface might be the most important piece of kit in your entire studio. But with so many on the market, how do you know which one is right for you? This web article explains some of the key aspects of Focusrite interface design, giving you the information you need to make an informed choice.

Birth of the Project Studio

The appearance of the home or project studio dates to around 1972 – when TEAC modified their quadraphonic 4-track home tape recorders to offer individual track recording and monitoring. The 2340 and the 3340 4-track reel-to-reel tape recorders were affordable and offered four tracks on ¼-inch tape. The 3340 and its relatives, used in conjunction with a small recording/mixing console, were capable of what were considered at the time excellent results.

Vintage Ad Promoting the TEAC 3340

Fostex came in with the A-8, with eight tracks on ¼-inch tape, and a small mixing console to go with it. 1979 saw the launch, under TEAC’s Tascam label, of the first cassette-based integrated 4-track recorder/mixer: the Portastudio 144, first of a long line of home studio systems using standard cassette tapes, often running at double speed.

Later developments included the advent of digital multitrack systems, including recorders like the Alesis ADAT (1992) that used S-VHS tapes, and the Tascam DA-88 using 8mm video format tapes. Later recorders used hard drives as these became cheaper, providing instant access to anywhere in a recording.

Alesis ADAT HD24 Hard Disk Recorder. Earlier ADAT models used Cassette Tape Recording

The Sonic Workstation

Electronic instruments had been able to communicate with each other via MIDI since it was standardized in 1983, and the advent of affordable home computers led to the personal computer-based sequencing software for recording, playback and editing of MIDI patterns on computers like the Atari ST and Apple Macintosh.

Some programs added stereo audio recording, editing and playback, creating the first general purpose “Digital Audio Workstations” (DAWs). Ultimately, many DAWs came to feature extensive multitrack recording, mixing and editing features: today they’re the most popular way to record – whether in back rooms or multi-room studios.

Computer Audio – the Upside

Computers initially lacked high quality built-in audio, but add-in sampler boards for personal computers, and computer-based musical instruments, had been around since the early 1980s. The arrival of keyboard samplers led the way to computer-based sample editors. One, Sound Designer, ultimately developed, via a stereo recording and editing program called Sound Tools, into the most popular multitrack DAW of all, Pro Tools, launched in 1991.

Modern Version of Pro Tools, the software engine that drives countless home/project studios

Simultaneously, computers offered improved on-board audio capability, and manufacturers such as Creative Technology introduced add-in cards for the Windows PC with the ability to capture and output audio. Thus the Sound Blaster was born. It was one of the first of many cards of this type.

Removable PC Sound Card

Computer Audio – the Downside

It’s tempting to use the on-board computer audio or soundcard for music recording. However, there are several reasons why this is not a good idea.

The interior of a computer is full of radio frequency signals. There are digital clocks, data streams and other control signals radiated into the enclosure, which are easily picked up by audio card circuitry and wiring. Digital noise can also come from the power rails, limiting the dynamic range of a recording and compromising its quality. Computer digital clocks may be insufficiently accurate or stable for quality work, contributing to jitter, impacting stereo imaging and audio transparency.

Meanwhile, the miniature connectors used to get sound into and out of a computer are unreliable and can cause hum and inadvertent disconnection. And consumer systems often cannot cope with the higher audio levels found in professional studio gear.

What you need instead is an audio interface.

What is an Audio Interface?

 An audio interface is an external unit that connects to your computer via one of several computer interfaces – such as USB, Firewire or Thunderbolt. It includes everything you need to get high-quality audio to and from your computer and DAW software.

The audio interface converts analog audio to digital at high quality and back again. Most audio sources, from vocals to guitars and many keyboards, are analog, and require an analog-to-digital converter (A-D). A digital-to-analog converter (D-A) gets the sound back into analog for monitoring, or for line level feeds to go into an analog mixing console. The quality of the digital conversion is one of three primary defining features of an audio interface.

Sample rates and bit depth

Most audio interfaces handle standard digital audio sample rates, including 44.1/48kHz (the standard for CD/DVD), 88.2/96kHz (found on DVD-Audio, Blu-Ray Disc and ‘High Resolution Audio’ streams and files), and up to 192kHz. It’s generally felt that higher sample rates provide higher sound quality, as the filters that are required in digital recording can affect the sound, and the further above the audio band they are, the better. However higher sample rates require more storage. 88.2/96kHz is probably a good balance.

Most converters operate at a ‘bit depth’ (or ‘word length’) of 24 bits. The word length defines the noise floor or dynamic range – the difference in loudness between the loudest and quietest sounds a system can handle. The 16-bit word length of Compact Disc is probably insufficient. 24 bits can capture sounds way below the limit of human hearing and is plenty.

Analog is the key: Circuitry

Analog circuit design is in many ways trickier than digital. In an environment that mixes the two, like in an interface, factors like board layout, component choice and position, and the enclosure itself become significant. And it’s the design of the microphone preamplifier that is most difficult of all to get right, and the most subjective when evaluating the sound of an interface.

The analog circuitry also allows you to use professional Recording Equipment in your studio. Audio interfaces feature connectors like XLRs and ¼-inch jacks. They handle professional levels and have plenty of headroom (the ability to take large signal levels without distortion).

Recording out of time: Latency

The third important factor in an interface is latency. “Round-trip” latency is the time it takes for a signal to go into the interface, pass into the computer, get processed in the DAW and come back out again. Latency matters: if you are recording with processing or effects and want to listen to them as you record, the latency must be as low as possible. More than three milliseconds or so and the delay between playing a note and hearing it is sufficiently long that it becomes painfully audible and impossible to play or sing against.

If the latency is too long to let you use plug-ins in real time, you have to monitor the input instead – either without the effects or with special separate signal processing.

Latency depends on the computer connection (USB, Thunderbolt etc), and the interface’s circuit and driver design.

Focusrite in a nutshell

Focusrite was founded in 1985 by leading British audio designer Rupert Neve to build a series of modules based around a mic preamp for the console in Sir George Martin’s AIR Studios. This ISA (Input Signal Amplifier) 110 was sold successfully as a stand-alone unit. The company also built a few extremely high quality Forte consoles.

Audio veteran Phil Dudderidge bought Focusrite in 1989, reissuing the original modules alongside some new designs, and built a new console, the Focusrite Studio Console. This led to a range of outboard devices, the Red Range – still highly regarded today. Focusrite built several ranges of professional audio modules over the following years, culminating in today’s ISA Range. Collaboration between Focusrite and Digidesign (now Avid, the makers of Pro Tools) resulted in the Mbox (2001) the first true integrated audio interface product from the company.

Focusrite ISA Mic Preamp

The company’s first interface series was the Saffire range, launched in 2005. Since then the company has added several more series, including the Scarlett USB interfaces, now in their second generation; the Clarett series of USB or Thunderbolt interfaces; and several industrial audio systems we won’t cover here.

Which connection? Firewire, USB and Thunderbolt

USB Type-A is the standard USB design, using a flat rectangular connector from a corresponding computer port. USB Type-B differs from USB Type-A in shape, and connects to a corresponding interface port. Scarlett interfaces can deliver Focusrite sound straight into your DAW via USB.

Scarlett USB audio interfaces utilize the USB 2.0 protocol. This is because the USB 3.0 protocol will deliver no round-trip latency benefits over USB 2.0. Although USB 3.0 offers greater bandwidth than USB 2.0, our Scarlett 18i20 provides more than enough bandwidth for delivering 18 channels of audio inputs and 20 channels of audio outputs simultaneously. There’s also a question of backwards compatibility. USB 2.0 devices work without any issue on USB 3.0 ports, however, the same can’t be said for USB 3.0 devices on USB 2.0 ports.

The ultra-low noise and distortion and wide dynamic range of Clarett can now be experienced with any Mac or PC supporting USB 2.0 and above. The Clarett USB series includes standard USB and USB Type-C cables to connect Mac or PC.

Thunderbolt 1 and Thunderbolt 2 ports have a DisplayPort connector, but can be differentiated from regular DisplayPorts by the Thunderbolt logo being printed above the port.

The Clarett Thunderbolt interfaces use Thunderbolt 1, which has a bandwidth of 10 Gbps – more than enough for audio recording and other applications. Clarett Thunderbolt interfaces can be connected to either Thunderbolt 1 or Thunderbolt 2 ports.

Focusrite interface options:

Sam Ash offers several Focusrite interface series, including the USB-based Scarlett series, and the USB or Thunderbolt-connected Clarett series.

Moving up from one range to another generally offers additional features and higher performance. Several interfaces can be expanded via ADAT light-pipe connections to provide additional inputs and sometimes outputs, in conjunction with products like Focusrite’s OctoPre 8-channel mic pre expanders.

Most interfaces include a useful selection of quality plug-ins including collaborations with leading suppliers via Focusrite’s Plug-In Collective initiative.

The Focusrite Scarlett Series

The third generation range of Scarlett interfaces are packed with awesome new features while continuing their legacy of incredible value and versatility. They now feature USB-C compatibility, plus super-low latency, and 24-bit/192kHz converters to give your recordings precision. The models in this series feature Scarlett microphone preamps, which now come with improved gain and dynamic range, as well as re-designed instrument inputs that can handle even seriously hot guitar pickups.

New for third gen, Focusrite has brought “Air Mode” to the Scarlett preamps—a feature previously found on their Clarett line. Air Mode simulates their classic, transformer based ISA range, giving the sound more top-end clarity and detail. It’s particularly useful for vocals and acoustic instruments.

The Scarlett units come with Focusrite Control for direct monitoring. You can use Control to configure your interface, including engaging Air Mode or pads on the mic preamps. The third gen of Focusrite Control has an added loopback feature for recording playback from your CPU – awesome for streamers or podcasters. Each unit also comes with DAW software and plenty of additional downloadable plugins.

Scarlett Models at a Glance

Scarlett Solo – The most compact Scarlett interface features a single mic preamp with switchable Air Mode, a high-headroom instrument input, and two hum-free balanced outputs. The third gen Solo is ideal for guitarists and singer-songwriters, giving you an easy way to make studio quality recordings at home. Also available in a studio pack.

Scarlett 2i2 – A compact, versatile 2×2 interface, boasting two mic inputs with third gen Scarlett preamps. This unit allows you to record studio quality audio anywhere, with two mic/line/instrument inputs, allowing simultaneous recording and playback of up to two channels, plus independently controllable headphone and monitor outputs. Also available in a studio pack.


Scarlett 4i4 – The 4i4 is a new addition to the Scarlett family. Replacing the 2i4, it was born with the third generation. This interface sports two beautiful sounding mic preamps, complete with Air Mode, plus two high headroom instrument inputs, and four balanced outputs.

Scarlett 8i6 – The 8i6 is also new for the third generation, replacing the 6i6. This unit now boasts four line inputs, and four balanced outputs on the rear of the unit, plus two preamps on the front. SPDIF I/O also gives you 2 additional digital channels to occupy.

Scarlett 18i8 – The 18i8 has four mic preamps on the front, with four line inputs on the back. There’s also a second pair of balanced outputs, plus alternate monitor switching—helpful for A/B comparisons. There’s an optical input for adding up to 8 mic preamps, with the help of a Focusrite Octopre unit. And to make this highly functional unit clean-looking, portable, and easy to use, the rack ears are now removable.

Scarlett 18i20 – The third generation 18i20 boasts extensive simultaneous I/O, comprising eight mic preamps, 18 inputs, and 20 outputs in total. It affords superior sound quality, talkback functionality, and onboard speaker switching. Improved A-D and D-A conversion ensures your recordings and playback will sound clear and pronounced up to 24-bit/192kHz, vital to helping you perfect your mix. The 18i20 is housed in a 1U rack-mountable enclosure.

The Clarett sound is available over USB or Thunderbolt. Both ranges offer three units varying in their I/O: Clarett 2Pre (10-in, 4-out), Clarett 4Pre (18-in, 8-out) and Clarett 8Pre (18-in, 20-out). Clarett 8PreX (26-in, 28-out) is only available as a Thunderbolt device.

Better, faster and easier, Clarett interfaces feature specially-designed high-performance, low noise mic pres with a clean, open and transparent sound. They also include the unique analogue “Air” effect, emulating the sound of Focusrite’s classic transformer-based mic preamps, adding a lift to vocals and acoustic instruments. Clarett includes precision digital conversion with 119dB dynamic range.

Included is Focusrite Control – a software mixer designed for easy configuration of monitoring and routing setups. The interface can also be controlled remotely from an iPhone or iPad via Focusrite iOS Control.



Clarett At A Glance

Clarett 2Pre (USB or Thunderbolt) – With dual mic preamps, it’s ideal for guitarists, singer-songwriters or in-the-box electronic musicians looking for minimal latency and maximum sound quality.


Clarett 4Pre (USB or Thunderbolt) – For studio-quality sound, performance and functionality, leave your gear plugged into this versatile and compact 4-mic pre interface.


Clarett 8Pre (USB or Thunderbolt) – Ultra-low latency, eight mic pres, 18×20 I/O, pristine sound quality and rock solid reliability in a 1U package for your studio setup or mobile recording rig.


Clarett 8PreX (Thunderbolt–only) – With the audible superiority of its performance confirmed recently in a blind shootout, this is the 26×28 flagship of our Clarett range. Clarett 8PreX provides separate jack (line) and XLR (mic) connectors so you can leave inputs permanently connected for instant access. There’s extensive digital I/O including dual ADAT I/O for expansion via products such as the Clarett OctoPre, and Word Clock I/O.

Focusrite was a contributor to this article.

Company Bio: Focusrite started as a collaboration between Rupert Neve and George Martin to augment the recording desks at Air Studios. Over the next 25 years Focusrite has become a leader in home studio recording making some of the world’s most reliable audio interfaces, mic preamps and more.

Company Email: [email protected]