The Ultimate Audio Interface Buyer’s Guide 2021


So you’re wondering which audio interface you should buy, rent or otherwise try out. In this comprehensive buyer’s guide, we’ll go through everything worth considering before you make any decisions about an audio interface.

If you’ve found yourself asking, “which audio interface should I buy?” this extensive resource is for you.

Please feel free to jump around this article and read all additional resources I have provided links to.

With that, let’s get into this comprehensive audio interface buyer’s guide to help you in your next interface purchase!

Related article:
Top 11 Best Audio Interface Brands In The World


Table Of Contents


What Is Your Audio Interface Budget?

The first thing to consider when making any purchase is your budget. Money can be a touchy subject for some, and so I’ll keep this section brief.

I would never advise anyone to overspend on any audio equipment. Know what you can realistically afford, and do your best to stay within those limitations, whatever they may be.

Audio interfaces, like many audio devices, range significantly in price. The market is rather large, and so there should be a good selection for any budget.

Note that some retailers offer payment plans, which could be an option.

Consider the cost to benefit ratio of the audio interface purchase. For example, if the interface is needed for business, perhaps stretching the budget is more appropriate. On the other hand, if you don’t plan on making money with the interface, perhaps a more conservative budget is appropriate.

Also, consider any additional accessories or upkeep that may be required for your audio interface.

Only you can determine your budget. All I’m here to say is that you should consider it.

Related My New Microphone article:
How Much Do Audio Interfaces Cost? (With Pricing Examples)

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The Inputs/Outputs (I/O) Configuration Of The Audio Interface

The I/O configuration is arguably the most important specification of a given audio interface. The number of inputs and outputs, along with their connection types and additional features, will largely determine the utility of the audio interface and whether you should buy it or not.

When considering the number of inputs and outputs in an audio interface, do your best to future-proof your investment. It’s critical that we choose an interface that will serve our I/O needs now, but take a minute to consider what you’ll need further down the line.

Audio Interface Audio Inputs

For instance, if you’re a singer-songwriter, you may only need two inputs (one for a vocal mic and one for a guitar, for example). Two inputs will also allow for stereo miking techniques or stereo instruments to connect just fine.

At the other extreme, if you’re planning on running live-off-the-floor sessions, you’ll need enough inputs for all instruments (including all those drum mics) and vocals. These inputs add up quickly in these circumstances!

Audio Interface Audio Outputs

With outputs, many bedroom producers and home studio owners only need a stereo pair or two for their monitors and one or two headphone outs.

However, many professional mixing and mastering engineers opt for multiple pairs of monitors to switch between different listening “environments.” Furthermore, having multiple headphone outputs will generally allow different headphone mixes to be outputted, which is great for sessions with multiple musicians, each of whom wants a different headphone mix.

Many audio interfaces with larger I/O counts will come with proprietary software that allows users to route the audio interface as they see fit. These interfaces facilitate the aforementioned monitor switching and numerous headphone mixes by routing the interface appropriately as a standalone unit or with the computer’s digital audio workstation.

So, take your time and consider the I/O configuration of your audio interface purchase.

Other Inputs & Outputs Worth Noting

Beyond the audio inputs and outputs, there are other I/O found in audio interface designs worth discussing. Let’s run through them here.

MIDI (Musical Instrument Digital Interface) I/O: MIDI inputs and outputs carry MIDI data to and from the audio interface. A single MIDI cable can carry up to sixteen channels of information, including on/off data, notation, pitch, velocity, vibrato, panning, clock signals, and much more.

Word Clock I/O: word clock tells an analog-digital converter and/or digital-analog converter when to sample the audio. For everything in a digital audio system to work properly together, they must not only have the same sample rate but also be synced to the same word clock. Audio interface word clock outputs effectively output the interface’s internally generated word clock, allowing it to be the master of other devices. Conversely, word clock inputs allow the audio interface to slave to a master word clock.

Remote Control Input: some audio interface designs go as far as to include remote control capabilities over some of their features.

Typical I/O Connectors

Let’s now consider the typical I/O connector types we’ll find on audio interfaces and the signals they tend to carry.

1/4 Jacks:
• instrument (Hi-Z) inputs
• headphone outputs
• monitor outputs
• footswitches

XLR:
• mic inputs
• line inputs
• instrument inputs (Hi-Z)
• monitor outputs
• 2-channel AES/EBU

Combo Jacks:
• mic/line/instrument inputs

Optical:
• ADAT Lightpipe
• S/PDIF (Sony/Philips Digital Interface)
• S/MUX (Sample Multiplexing)
• MADI (Multichannel Audio Digital Interface)

Coaxial (RCA):
• monitor outputs
• S/PDIF
• word clock inputs
• word clock outputs

Coaxial (BNC):
• monitor outputs
• word clock inputs
• word clock outputs
• MADI

DB-25:
• line inputs
• line outputs
• 8-channel AES/EBU (TASCAM & Yamaha)

DIN 41524:
• MIDI inputs
• MIDI outputs

RS-485/RS-422:
• MIDI inputs
• MIDI outputs

Ethernet: interface connection (data I/O)
• Dante
• AVB (Audio Video Bridging)

USB:
• interface connection (data I/O)
• memory
• remote control

Thunderbolt: interface connection (data I/O)

Firewire: interface connection (data I/O)

We’ll have a further discussion on the interface connections in the upcoming Connectivity Options Of The Audio Interface section.

Simultaneous I/O

Another specification worth considering, especially in more complex audio interfaces, is the simultaneous I/O. This specification will tell us, written as “X x Y,” how many audio inputs (X) and outputs (Y) can be used at the same time. Note that this specification generally does not include headphone outputs.

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DACs Vs. Audio Interfaces

Standalone DACs (digital-analog converters) are somewhat popular, especially in the audiophile market. DACs technically interface with the computer/digital device, so how are they different from what are known as audio interfaces?

First of all, audio interfaces act as digital-analog converters and as analog-digital converters. DACs, on the other hand, are designed only for digital-analog conversion.

DACs are generally employed in higher-end systems where the built-in DAC of the digital playback device (laptop, cell phone, etc.) is the weakest link in the signal chain and causes noise or distortion in the signal.

Driving high-quality headphones with a dedicated DAC may improve the listening experience versus plugging the headphones directly into the playback device. The same is true for driving speakers, though further amplification will be required post-DAC.

Audio interfaces have built-in DACs that are also generally superior to consumer-grade sound cards. These interfaces also drive headphones and speakers and require analog audio outputs to do so.

So DACs act as the output audio device of the computer and convert the computer’s digital audio to analog audio. Audio interfaces can be selected as the computer’s audio input and output device and therefore require ADCs and DACs.

Related articles:
The Ultimate DAC (Digital-Analog Converter) Buyer’s Guide
Top 9 Best Portable DAC (Digital-Analog Converter) Brands
Top 11 Best Desktop DAC (Digital-Analog Converter) Brands

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Audio Interface Form Factor

Let’s consider the typical form factors for audio interfaces. They are:

Desktop Audio Interfaces

Desktop audio interfaces range in size and are meant to sit on a desktop, hence the name. They are not designed to fit into studio racks, nor are they particularly portable (designed to move around while in use).

Rackmount Audio Interfaces

Rackmount audio interfaces are designed to incorporate into 19″ studio racks. Of course, these interfaces can be placed on desktops as well. They are not portable.

Note that some audio interfaces will come with ears to effectively integrate them into a rack if need be.

Portable Audio Interfaces

Portable audio interfaces are designed mostly as single-channel in-line interfaces and can be quickly patched in and moved around during audio recording/playback.

Many portable interfaces are simple XLR-to-USB or TRS-to-USB converters.

Other Devices With Built-In Audio Interfaces

Moving beyond standalone audio interfaces, there are other audio devices worth considering that have built-in audio interfaces. Some examples include:

  • Audio mixers and consoles
  • 500 Series chassis
  • USB microphones with headphone outputs

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System Requirements

The system requirements for audio interfaces are typically solely in regards to the operating system (the version or macOS or Windows) and sometimes account for CPU requirements.

A computer’s operating system manages its memory and processes along with all of its software and hardware. The OS must be compatible with the interface for proper communicating between the two.

These aren’t the most exciting specs but are worth the brief mention in this article.

Back to the Table Of Contents.


Connectivity Options Of The Audio Interface

Let’s move on to another critical specification of prospective audio interfaces: interface connectivity.

There are differences in the way audio interfaces can connect to their computer devices. When choosing an audio interface, it’s important to consider the specifications of each connection. More immediately, though, we must consider what connections are available on our computer now, as well as which connections we may be planning to use in the future.

Before we get to each interface connection type, I should mention that audio interfaces are either powered by the computer via their interface connection or by a dedicated power supply (often standard IEC AC cables).

I should also state that while new USB, Thunderbolt and FireWire generations are designed to be backward-compatible. There are certain instances where issues may arise when attempting to connect new-gen and old-gen technology together. Unfortunately, it’s difficult to anticipate these issues, so I suggest doing research on forums regarding the specific connections you plan on using, especially if they are from different generations of the technologies mentioned above.

With that all said, let’s examine the various connectivity options for audio interfaces:

  • USB
  • Thunderbolt
  • FireWire
  • PCI Express
  • DigiLink
  • Dante?

USB

USB (Universal Serial Bus) is among the most popular standard for digital connections in consumer audio and also finds itself in professional applications.

Though not as fast as Thunderbolt and PCI/PCIe, which we’ll discuss shortly, USB is common, which is a big benefit.

USB 3.0 can achieve 5 Gbps bandwidth, though real-world performance is typically around 3.2Gbps. USB 2.0 is slower, capable of 0.48 Gbps, though generally performs around 0.28 Gbps.

Furthermore, USB can provide adequate power from the computer to many USB interfaces, thereby removing the need for external power supplies. This can be a big benefit for mobile recording units.

Thunderbolt

Thunderbolt is at the top in terms of speed and offers super-low latency for its audio interfaces. It has largely become standard in the audio interface market. This hardware interface standard is developed by Intel, though Apple is a strong collaborator. Therefore, Thunderbolt is rather common with Apple computers.

Thunderbolt 3 boasts an impressive bandwidth of 40 Gbps, while Thunderbolt 2 can achieve 20 Gbps and Thunderbolt 1 offers 20 Gbps over two channels (10 Gbps each).

Many of the high-end audio interfaces on the market make use of this superb connection.

Though Thunderbolt has 15 watts of power delivery on copper cables (and none on optical cables), Thunderbolt audio interfaces will require external power supplies.

FireWire

FireWire is another serial bus protocol. Since FireWire was largely developed by Apple (with support from Sony and Panasonic), it does enjoy some compatibility with Thunderbolt. That being said, FireWire has largely been replaced with Thunderbolt (the last Apple computer with FireWire was released in 2014).

FireWire audio interfaces are still on the market, though their performance is generally worse than the newest USB and Thunderbolt standards.

FireWire 800 maxes out at 0.8 Gbps bandwidth, while the older FireWire 400 has half that at 0.4 Gbps bandwidth.

PCI Express

PCI Express (PCIe) or Peripheral Component Interconnect Express is a connection standard that connects directly to a computer’s motherboard. PCIe audio interfaces are essentially aftermarket internal sound cards.

These cards aren’t overly practical with laptops since laptops aren’t designed to be taken apart and modded with large audio interfaces.

Rather, PCIe audio interfaces are generally considered by studio owners and those who have stationary computers for their work.

PCIe interfaces have historically outperformed USB, Thunderbolt and FireWire audio interfaces in latency and track count. However, recent developments in Thunderbolt have made it competitive with PCIe.

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Ethernet Audio Interfaces

Now that we know about the typical connections between audio interfaces and computers, let’s discuss ethernet audio interfaces and how network audio or “audio over Ethernet” (AoE) works. If the audio interface you’re interested in has an Ethernet port, it has AoE capabilities.

AoE utilizes an Ethernet-based network to distribute real-time digital audio via digital Cat5, Cat5e, or Cat6 cables. The number of channels available is dependent on the open or proprietary standard.

For home studios, Ethernet audio interfaces can be overlooked. However, in large-scale studios, broadcast centres or live venues, sending audio via an Ethernet network can potentially replace hundreds of cables and snakes, making setup, troubleshooting and tear down so much easier.

Furthermore, network audio benefits from superb expandability, allowing a single Ethernet audio interface to be a modular component of a much larger network system.

Audinate’s Dante, Allen & Heath’s dSNAKE are popular proprietary platforms. AVB (Audio Video Bridging) is a great open standard.

Some brand’s interfaces utilize their own proprietary Ethernet platforms, including Behringer’s Ultranet and Waves’ SoundGrid.

Allen & Heath is featured in the following My New Microphone articles:
Top 10 Best Live Sound Mixing Board/Console Brands
Top 11 Best Mixing Board/Console Brands For Home Studios

Behringer is featured in the following My New Microphone articles:
Top 11 Best DAW Control Surface Brands In The World
Top 11 Best Eurorack Module Synth Brands In The World
Top 11 Best MIDI Controller Brands In The World
Top 11 Best Mixing Board/Console Brands For Home Studios
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Top 11 Best Direct Inject Audio Box Brands On The Market

Waves is featured in My New Microphone’s Top 11 Best Audio Plugin (VST/AU/AAX) Brands In The World.

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Audio Interface Features

Audio interfaces come with all sorts of features. Let’s discuss a few of the most popular features in this section:

Signal Level Monitoring

Signal level monitoring allows users to monitor inputs levels on the interface itself.

Phantom Power

Phantom power is a common inclusion on microphone preamplifiers that outputs +48V DC (ideally) on pins 2 and 3 of a connected XLR cable. Phantom power is used to power the active circuitry within many “non-tube” condenser microphones and active ribbon microphones.

Sometimes phantom power is available on a per-channel basis. Other designs will have multi-channel phantom power switched (1-4 and 5-8, for example).

Related My New Microphone articles:
What Is Phantom Power And How Does It Work With Microphones?
Will Phantom Power Damage My Ribbon Microphone?

High-Pass Filter

Some interfaces offer high-pass filters (HPFs) in their preamps to effectively filter low frequencies from the input signal. High-passing at the preamp stage can help clean up electromagnetic interference and mechanical noise/rumble before the signal is processed further.

Related My New Microphone articles:
What Is A Microphone High-Pass Filter And Why Use One?
Audio EQ: What Is A High-Pass Filter & How Do HPFs Work?

Phase Flip

Phase flip is another popular feature for preamps/inputs to have. As the name suggests, a phase flip switch will flip the phase (±180°) of the input signal.

Related My New Microphone article:
Microphone Polarity & Phase: How They Affect Mic Signals

Pad

Pads (passive attenuation devices) effectively reduce signal levels. Pads at the inputs of an audio interface allow users to bring down signal levels to avoid overloading the rest of the circuitry, including the analog-to-digital converter.

Related My New Microphone article:
What Is A Microphone Attenuation Pad And What Does It Do?

Low/High Impedance Switch

Input impedance switches allow users to switch the input impedance of an input to best suit the incoming signal. High impedance is particularly useful when recording passive guitar and bass directly.

Related My New Microphone articles:
Microphone Impedance: What Is It And Why Is It Important?
What Is A Good Microphone Output Impedance Rating?

Mic/Instrument Level Switch

Mic/instrument level switches change the signal level the input is designed to expect.

Mic level inputs expect mic level: the typical audio signal level of professional microphone outputs and mic preamplifier inputs. Nominal mic level is generally between 1 to 100 millivolts AC (-60 to -20 dBV). Mic level signals need amplification to reach line level for use in mixing consoles and DAWs.

Instrument level isn’t standardized, though instruments will generally output signal levels above mic level and require different specifications at their preamps.

The aforementioned low/high impedance switch will often double as the mic/instrument level switch or vice versa.

Direct Monitoring

Engaging direct monitoring causes the audio interface to send its post-preamp input signals directly to the headphone and monitor outputs, bypassing the computer altogether. This is useful for reducing the latency associated with A/D and D/A conversion and the buffer size of the computer.

Dedicated I/O Software

As mentioned previously, some larger interfaces feature their own dedicated software for complex routing within the interface. These software programs allow users more flexibility within the interface and between the interface and their DAW of choice.

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A/D Resolution Specifications: Bit-Depth & Sample Rate

Digital audio signals aim to represent analog audio signals as digital information. While analog waveforms are continuous, digital waveforms are discrete.

The resolution of such digital audio waveforms is dependent on the bit-depth and the sample rate.

Sample rate is the number of times the digital audio signal is sampled per second.

Bit-depth refers to the number of potential amplitude values that can be assigned to each sample.

These specifications refer to the analog-to-digital and digital-to-analog conversion processes within the interface and can commonly be found together as the “A/D Resolution” spec. Oftentimes this specification will refer to the maximum bit-depth and sample rate of the interface. Reading the manual, we will often find a list of supported sample rates and bit-depths.

Common sample rates include:

  • 44.1 kHz
  • 48 kHz
  • 88.2 kHz
  • 96 kHz
  • 176.4 kHz
  • 192 kHz

Most interfaces will have the standard 24-bit bit-depth (16,777,215 possible amplitude values). 16-bit (65,536) is another common bit-depth for audio but is typically only found in entry-level audio interfaces.

When it comes to bit-depth, the audio interface and digital audio workstation don’t necessarily have to have the same specification. For example, 32-bit floating is becoming popular in DAWs and works perfectly well with 24-bit interfaces. These bit-depths will be easily converted in real-time by the computer.

With sample rate, however, it’s a different story. The interface’s sample rate should match the DAW session’s sample rate for proper playback and especially for proper recording.

If the sample rates are different, there will be speed and pitch differences, as the audio at one sample rate is recorded or played back at a different sample rate.

Imagine having 48 kHz audio (48,000 samples per second) and playing it back in a 96 kHz session (which reads 96,000 samples per second). Since 96k is double 48k, each second of 48k audio (48,000 samples) would fit into half a second of 96k audio (96,000 samples). This would cause the audio to playback at double speed and double-pitch.

Ensuring identical sample rates when recording and playing back audio is essential for proper speed and pitch. Fortunately for us, most interfaces have automatic sample rate conversion (SRC), and most DAWs have options for SRC. The supported sample rates of an audio interface should automatically adjust to the DAW’s sample rate.

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Built-in Preamplifier Specifications

Many of the audio interfaces on the market have their own built-in preamps for their individual inputs. Understanding the preamplifier (both microphone and instrument) specifications can help us make more informed decisions regarding our interface purchase.

Specifications worth checking out include:

  • Maximum input level: how loud can the input analog signal be before the internal circuitry is overloaded. High values can accept stronger input signals and give us more headroom to work with at the input.
  • Gain: how many dB of clean gain can the interface provide. Note that dynamic microphones typically require more gain and passive ribbon microphones definitely require lots of clean gain.
  • Equivalent input noise (EIN): the inherent noise produced by the preamplifier, measured in decibels A-weighted (dBA). This noise is added to the audio signal as it is amplified through the preamp. The lower the rating, the less noise the audio interface will introduce into the signal.
  • Impedance: the input impedance of the preamp, which acts as the load impedance to the connected microphone or instrument. Ensure the input impedance is much higher than the mic or instrument output impedance for optimal signal transfer.

Related My New Microphone article:
Complete Guide To Microphone Preamplifier Specifications

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Latency Specifications

Latency is effectively the delay an audio system experiences between the initial input and the final output.

Roundtrip latency in audio interfaces refers to the time it takes for a signal (from an instrument or microphone) to get from an analog input on the interface, through the analog-to-digital converters, into a digital audio workstation, back to the interface, and through the digital-to-analog converters to the analog outputs.

Technically, we should include the time it takes for sound to travel through its medium in the overall latency calculation, but this is usually negligible due to close-miking and the typical proximity between our ears and the monitors or headphones.

In addition to the ADCs and DACs within the audio interface, the DAW’s buffer size will also play a role in overall latency.

Buffer size is the amount of time it takes for your computer to process any incoming audio signal, measured in samples. This is typically adjustable with the DAW. To find out the resulting latency, divide the buffer size by the project’s sample rate. Increasing buffer size increases latency while decreasing the demands on CPU and RAM.

Many audio interfaces will allow direct monitoring for near zero-latency monitoring. Direct monitoring effectively bypasses the computer altogether.

Generally speaking, latency figures below 12 ms won’t be perceived by humans, and we really only begin to hear echo at delay times above 20 ms. That being said, the closer we can get to 0 ms, the more accurate our monitoring and more efficient our system will be. Therefore, opting for an audio interface with a low latency specification is ideal.

Related My New Microphone article:
How To Fix Microphone Echo And Latency In Your Computer (7 Methods)

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Built-in Digital Signal Processing

Some audio interfaces offer built-in DSP capabilities. The processing chips in these devices will run DSP plugins, thereby freeing up the computer’s CPU (which is needed to run native plugins).

Nowadays, most new computers are more than capable of running enough plugins for DAW projects. DSP plugins and dedicated DSP cards and interfaces were originally developed when computers weren’t powerful enough to run great numbers of plugins simultaneously without significant latency and system errors.

So DSP offloading isn’t really necessary in today’s technology, though it can improve system performance. Note that latency is not completely eliminated as the DSP interface still has to stream the audio data to and from the computer.

Note, too, that built-in DSP interface technology is still largely proprietary. This means that a company’s DSP interface will only run its own plugins formats. When it comes to the industry leaders in this space, UAD (Universal Audio Digital) is a popular option. Avid’s AAX DSP is a format standard for which several plugin developers have developed plugins (with proper licensing requirements). There are plenty of other proprietary DSP hardware interface options on the market.

Many interfaces that have internal DSP will come with a bundle of plugins.

Offloading processing to your interface could be optimal for your setup, especially if your computer’s CPU specifications are lacking. That being said, do your research to ensure the DSP interface will run the plugins you need it to!

Universal Audio is featured in the following My New Microphone articles:
Top 11 Best Audio Interface Brands In The World
Top 13 Best Microphone Preamplifier Brands In The World
Top 11 Best Audio Plugin (VST/AU/AAX) Brands In The World
Top 11 Best Audio Compressor Brands In The World

Avid is featured in the following My New Microphone articles:
Top 11 Best Audio Interface Brands In The World
Top 11 Best DAW Control Surface Brands In The World
Top 10 Best Live Sound Mixing Board/Console Brands

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This article has been approved in accordance with the My New Microphone Editorial Policy.

Arthur

Arthur is the owner of Fox Media Tech and author of My New Microphone. He's an audio engineer by trade and works on contract in his home country of Canada. When not blogging on MNM, he's likely hiking outdoors and blogging at Hikers' Movement (hikersmovement.com) or composing music for media. Check out his Pond5 and AudioJungle accounts.

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