Audio Interface: Types, What It Is and Functions

Audio interfaces are used to connect microphones and other audio devices, serving as a bridge between the analog and digital worlds. In this blog, we will learn about the features, types, and common audio cables of audio interfaces.

What is an audio interface?

An audio interface is a device specifically designed to connect audio devices to computers. Its primary function is to provide input and output of audio signals and convert between analog and digital signals.

In simple terms, an audio interface is a "bridge" for audio, allowing microphones, musical instruments, music players, and other audio sources to be recognized and processed by the computer, and allowing the sound from the computer to be clearly transmitted to external devices such as amplifiers or speakers.

Digital Mixer-Amplifier

What functions does an audio interface perform?

Audio interfaces are a key component of any audio system. They are a series of ports or connectors on the back or front of a device. These ports are used to connect various audio devices and convert audio signals from one type to another.

Through these connectors, we can connect microphones, musical instruments, music players, speakers, and more. This allows the sound to be transmitted in the system in the correct manner for clear and smooth playback.

1. Signal Conversion

One of the most important functions of an audio interface is signal conversion. In reality, sound exists in the form of analog signals, which are waveforms in which voltage continuously changes over time. But many modern devices, including computers, digital mixers, network audio systems, etc., can only process digital signals - binary data consisting of "0" and "1".

In order for these devices to understand sound, the audio interface first performs an analog-to-digital conversion, turning the analog signal into a digital signal. This process is called analog-to-digital conversion (ADC). When we speak, the microphone converts the sound into an analog electrical signal, and the audio interface then converts this electrical signal into digital data through sampling and encoding steps for the system to process.

When a device needs to output sound, such as when playing music or voice, the audio interface performs a digital-to-analog conversion (DAC), restoring the digital signal to an analog electrical signal, and then sending it to a power amplifier or speaker so that we can ultimately hear the sound.

You could say that an audio interface is like a two-way translator, helping the analog and digital worlds communicate freely.

2. Signal Routing

In addition to converting signals, an audio interface is also responsible for organizing the direction of the audio signal flow - this is the signal routing function. In a complete audio system, the audio signal often needs to pass through several processing stages, such as from a microphone to a preamplifier, then to an analog-to-digital converter, and then transmitted to a computer or digital control system.

These transmission paths are not fixed, but can be flexibly configured to suit different applications. The audio interface acts as this "traffic controller", ensuring that each signal flows in the correct order.

In a digital audio system, users can also set up logical routing, allowing the audio signal to be output from a specific program channel, then sent to a hardware effects processor for processing, and finally sent to a monitor speaker for monitoring.

This flexible signal path configuration allows the audio interface to not only handle simple input and output, but also meet the complex needs of recording, mixing, broadcasting, and more. Some high-end audio interfaces even support multi-channel parallel transmission, audio mixing matrix, and real-time bypass operations, which greatly improves the adaptability and efficiency of the system.

3. Connection Adaptation

The last important function is to connect and adapt different types of audio devices. In reality, different devices use different types of audio interfaces, voltage standards, and impedance characteristics. An audio interface must have good compatibility to ensure normal operation between different devices.

Common types of physical interfaces include XLR, TRS, TS, and RCA.

To further ensure compatibility and sound quality, the audio interface also performs some technical processing on the signal itself. For example, when connecting high-impedance devices such as guitars, the interface provides a Hi-Z input channel so that the signal can be correctly input without distortion. For devices such as microphones with very weak signals, the interface increases the level through the preamplifier to the working range required by the system.

In short, an audio interface is a bridge between audio devices, signal conversion, and system adaptation.

Types of Audio Interfaces

Audio signal interfaces can be divided into analog audio interfaces and digital audio interfaces according to the type of signals transmitted; They can be divided into balanced interfaces and unbalanced interfaces according to the connection method.

Analog Audio Interface: Analog audio is a technology for transmitting, recording, reproducing and processing audio signals in an analog state. Similar to the game of broken telephone in everyday life, the transmission of analog audio interfaces is intuitive and easy to implement, but relatively distorted and unstable. Common analog audio interfaces are TRS interfaces, XLR connectors and RCA connectors.

Digital Audio Interface: Digital audio is a technology for recording, storing, editing, compressing or reproducing audio by digital means. Transmitting digital audio signals requires first sampling the analog signal, then quantizing the sampled values ​​into different levels, and then encoding the different quantized levels.

One level corresponds to a group of binary digits, and eventually a series of binary digits are obtained, completing the conversion of analog signals into digital signals. Therefore, the higher the sampling rate and quantization level, the higher the accuracy of the analog-to-digital conversion and the stronger the signal recovery ability.

Common digital audio interfaces are the physical AES/EBU interface, S/PDIF interface, coaxial interface, and fiber optic interface.

Balanced Interface and Unbalanced Interface

A balanced transmission interface uses two channels to transmit signals with the same voltage but opposite phases. The receiving device subtracts the two sets of signals, and the interference signal is canceled, thereby obtaining a high-quality analog signal. Common balanced audio transmission interfaces are TRS interfaces and XLR connectors.

An unbalanced transmission interface consists of a signal line responsible for transmitting the signal and a ground line. During the signal transmission process, the wire will be exposed to external interference and amplified by a microphone amplifier or power amplifier. Due to its poor noise-resistance ability, noisy sound is easily output. Common unbalanced audio transmission interfaces are TS interfaces and RCA connectors.

Common Audio Interfaces

1. TRS

TRS is similar to a regular headphone jack. Its full name is Tip-Ring-Sleeve. The connector usually has three metal segments corresponding to the left channel, right channel, and ground. It can transmit stereo audio signals or balanced mono signals.

It is durable and suitable for repeated plugging and unplugging. It can suppress noise interference well within a certain distance. Common sizes are 6.35mm and 3.5mm.

2. TS

The TS interface is similar in appearance to TRS, but it only has two metal segments: one is the signal end and the other is the ground wire, and it cannot carry balanced signals. It is more often used for unbalanced audio connections, such as connecting electric guitars, electric bass guitars, or other instruments to speakers or mixers.

This interface has a simple structure, but its ability to resist interference is weak, and it is usually only suitable for use over short distances.

3. XLR

XLR interface is a professional-grade audio interface consisting of a three-pin connector (male) and a locking device (female). It can transmit balanced audio signals and is the most commonly used interface type for professional microphones.

The structure of the XLR interface is very stable. After inserting, it is fixed with a latch and will not wobble. It can effectively suppress external interference and keep the sound quality clear and stable even when transmitting over long distances. In stage sound reinforcement, broadcasting systems and recording studios, XLR is a very common standard interface.