Audio Interface Definitions

If you've been looking at the specifications of audio interfaces and you're wondering what all that jargon means, then this glossary will help you understand the technical terminology.


Audio Interface

Sometimes also referred to as an Audio Adapter or Sound Card. In its basic form it's a device used to take an analog audio signal and turn it into a digital signal which is then usually sent to a computer for use in recording audio. It then also accepts digital audio back from the computer in order to send the sound to monitors (speakers). They may also come with many other features and functionality such as headphone outputs, level monitoring etc. These days they are usually external devices which you connect to your computer via USB or FireWire - Sound Cards used to perform the same function but were typically mounted inside the computer and connected to a panel on the outside of the PC where you would plug in your instruments, headphones, monitors etc.


A protocol for sending and receiving digital audio using optical fiber cables. It can transmit up to 8 channels of digital audio at 44.1/48kHz sample rates, but it can transfer higher sample rates if fewer channels are used. It was originally developed by Alesis for use with their ADAT recorders in the early 1990s, but has since been widely adopted by professional audio equipment manufacturers.

Bit Depth

This represents the 'dynamic resolution' of digital audio - or to put it more simply, it determines the difference between the loudest and quietest sounds which can be recorded and played back, and the size of the volume difference between each bit. The higher the bit depth, the higher quality the volume resolution is. People can hear up to 20-bits of dynamic range, but audio CDs only have 16-bits of dynamic resolution. Since CDs were first introduced many other formats such as Audio DVDs and Blu-Ray discs, as well as digital audio files sold by businesses like iTunes and Amazon, now support higher bit depths, and you will generally want an audio interface with at least 24-bits.

Bundled Software

Some interfaces also come with additional software such as DAWs, Plugins, and Sample & Loop Packs, to allow you to get up and running producing music as soon as you take the interface out of the box. Usually these will be cut-down 'Lite' versions of commercial software, and you will generally want to get a full DAW if you're serious about recording music.

Connection Type

In the context of audio interfaces this refers to the protocol or method used to connect your adapter to your computer. The main types of connections are USB and FireWire. USB comes in a few different varieties: 3.0, 2.0, and 2.0 30-pin (mainly for use with iPads). FireWire typically comes as FireWire 400 but also less frequently FireWire 800 - the number refers to how many Megabits per second it can transfer. Most PCs and Tablets use USB, while FireWire is Apple's version of USB which their desktop computers generally use.

Direct Zero Latency Monitoring

Sometimes also simply referred to as "Direct Monitoring" or “Zero latency Monitoring". It connects the input of the interface directly to the output so you can listen to the sound before any digital audio processing is done. This prevents any delay (latency) in hearing the sound that is being recorded.

DSP Effects

DSP stands for "Digital Signal Processing". Audio interfaces with DSP Effects are capable of providing audio effects such as reverb and EQ on the device itself during either recording or playback. One of the main uses for this in a home recording studio is to apply a compressor/limiter before the digital audio is sent to your computer. Other effects can also be applied in order to reduce the load on your computer's CPU while recording, however most professional recording engineers prefer to record a 'clean' sound and apply effects later during the mixdown process thus giving you much more flexibility and control over the final result.

Headphone Outputs

These allow you to plug headphones directly into your audio interface so you can listen to the audio as you are capturing it without having to use speakers/monitors - quite useful when recording with microphones and you don't want the backing tracks to 'spill over' into the track you are currently recording.

Instrument Inputs

These have a much higher level of impedance compared to Line Inputs (typically around 50k ohms), and are designed to work with instruments such as guitar and bass. Note that electronic instruments such as keyboards output a 'line level' and should not be connected to an Instrument Input but rather they should be plugged into an Line Input instead.

iPad - Connects to iPad | Officially made for iPad

On this website we let you know whether or not each interface we've presented can be used with an iPad. Ones labeled with "Officially made for iPad" are licensed by Apple and have been tested and officially certified as meeting Apple's standards for use with iOS devices such as the iPad.

Line Inputs

These are known as 'line level' inputs which accept analog audio signals from microphones and other audio devices which send a 'line level' signal. This can also include some instruments such as keyboards or synths. They typically accept an input impedance of around 100 to 200 ohms.

MIDI Inputs / Outputs

MIDI stands for "Musical Instrument Digital Interface" and it enables MIDI capable computer interfaces, instruments, effects units, controllers etc. to communicate with each other. The typical use in a home studio is to send and receive note and control information between MIDI controllers or keyboards and your computer. E.G. you would plug your MIDI capable keyboard or controller into the MIDI input on your audio interface to record what you play and control other devices such as hardware and software synthesizers. MIDI has had such a profound impact on both live and recorded music production that in 2012 the two key developers of the standard, Dave Smith and Kutaro Kakehashi, were presented with the Technical Grammy Award for their work developing it in 1983.

Phantom Power

This is a DC electric current which is sent from the audio interface to microphones which need electricity to operate - typically these would be condenser microphones. Most audio interfaces use a 48 V current as that is the standard for most microphones which require phantom power, although 24 V and 12 V phantom power does exist but is rarely employed by the type of microphones used in either professional or home recording studios. If any of your microphone's specifications say they need phantom power then you must get an audio interface with this capability - you don't need to do anything else - just plug them in and they'll draw current from the interface automatically.

Routing Software

Additional software for your computer which is supplied with some audio interfaces so that you can control which sockets on the interface connect to which inputs on your computer software such as your DAW (Digital Audio Workstation).

Sample Rate

This is the number of times per second that the audio adapter 'listens' to the analog audio and converts it into digital information, and for converting the digital audio back into analog to send to speakers or studio monitors. CDs use 44.1kHz and DVDs use 48kHz. 'kHz' means how many thousand times per second the audio is sampled. The highest frequency of audio that can be recorded or played back is half the sample rate, so a CD can only produce audio frequencies up to 22.05 kHz. Given that most adults can only hear up to about 20kHz, you would think that an audio interface working at 44.1kHz would be enough, however most audio engineers prefer to record at double or even quadruple the standard rates to ensure that any artifacts created by digital audio filters in the digital audio signal path are well outside hearing ranges. Professional software based DAWs (Digital Audio Workstations) can work with 96kHz, and sometimes even 192kHz, and most recording studios will employ audio interfaces that use these higher rates. It is generally agreed by most professional recording engineers that higher sample rates lead to higher quality sound even when the final product is mixed down to 44.1kHz for CDs.


This stands for "Sony/Philips Digital Interconnect Format". It is a protocol which has been widely adopted by electronic audio equipment manufacturers for sending and receiving stereo digital audio using phono connectors. It is used by many audio interfaces as well as other outboard gear such as effects units and even some keyboards and stand-alone digital audio workstations.

Word Clock I/O

A protocol for synchronizing digital audio sampling rates which is used on some older audio interfaces as well as some high-end products. A Word Clock sends a signal to tell the digital audio converters when to take or play back each individual sample. It is generally no longer required as most modern equipment uses digital audio protocols which have timing information embedded in them. If you're unsure about whether or not you need this feature then you probably don't, so don't worry about it.