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What is an audio interface?

What is an audio interface?

An audio interface is a device for connecting microphones or musical instruments to a computer. It is indispensable for music production on a computer because it allows you to capture audio on a computer and record it via music production software. In addition, it is possible to reproduce the captured sound and computer sound with high sound quality.

It converts analog audio signals from microphones and musical instruments into digital data that can be handled by a computer. Similarly, it converts the digital signal on the computer to analog so that the audio data can be viewed.

Often, the computer itself has a microphone input and headphone output, but in many cases the voice capabilities of the computer are simple, and it is possible to input voice at the minimum conversation level and perform simple playback. In fact, most computers are like that. The audio interface is a step up from the simple sound function of the computer!

What you can do with an audio interface

You can record the sound of a microphone or musical instrument via music production software.
However, recently, there are increasing cases where the audio interface is used not only for recording but also for streaming using streaming software and video services.
Also, it can be used for listening to music on iTunes or You Tube with high sound quality! This is also very useful.

In some cases, the recording itself can be performed using the microphone input on the computer. However, if you have problems with sound delay, noise, muffled sound, crackling sound, etc., you may be able to solve these problems by connecting via an audio interface and using a compatible microphone.
* In many cases, the microphone input of the computer is for plug-in power (3.5 mm). Plug-in power microphones cannot be used with audio interfaces (except for some models) even if a conversion adapter is used.

In addition, the computer itself often has only one microphone input and one headphone output, but there are various types of input/output terminals on audio interfaces. For example, there are some with a lot of microphone inputs for those who record drums, some with minimum inputs/outputs for those who mainly enjoy simple recording at home, some that are mainly for home recording but outboard. For those who want to use effects, a variety of inputs/outputs can be selected according to the application, such as a type with 4ch output. However, please note that the number of channels that can be used may be limited depending on the software and streaming service.

What you can do with an audio interface

You can input microphones and musical instruments with high sound quality.
High-quality sound can be played back including computer sounds and recorded sounds.
Sound delay (latency) can be improved
Multiple microphones and instruments can be input

Musical instruments that can be connected

Microphones

You can use condenser microphones and dynamic microphones. Please note that many plug-in power microphones cannot be used.
Phantom power is required when using condenser microphones, but many audio interfaces also have Phantom power. (Be sure to check when purchasing.)
It is also possible to input multiple microphones to the audio interface and record from various angles and distances at the same time. You can also record different instruments at the same time. (This will depend on the features and functions of the software as well)

Guitar, bass

Of course, if you use an electric guitar, you can connect it to an amplifier and set up a microphone in front of the amplifier to record. But if you have an audio interface with an input terminal that supports high impedance such as Hi-Z, you can connect the guitar directly to audio interface with a shield. In that case, you will need to create your desired sound with an amplifier simulator on the software side.

Keyboards, synthesizers

Audio interface models with line input can be connected to keyboards and synthesizer audio outputs.
If you can input in stereo, you can connect the synth or keyboards with a dual cable as shown below.

CLASSIC PRO / DPP030

mixer

If the audio interface has a small number of inputs, it is possible to combine various instruments with a mixer before sending them to the audio interface. Especially in streaming, there are many cases where such connections are necessary.
* There are also mixers available that have an audio interface function.

Rhythm machine, sampler

Like a synthesizer, it can be connected to a terminal that allows line input.

How to connect to a computer

USB and Thunderbolt are the mainstream for computers, but Firewire, Ethernet, and PCIe connections are also possible. Select according to the terminal installed in your computer. Basically, there is no difference in sound quality with the different connection methods. In many cases, models with ultra-low latency and models equipped with the DSP function described later use Thunderbolt or USB 3.0, which have high transmission speeds.

USB

There are several types such as USB 2.0 and 3.0, and type-C terminals. USB 2.0 is a terminal that has been used for a long time, but it is also highly stable and is still installed in a lot of high-spec audio interfaces. Since USB 3.0 is capable of high-speed communication, it is suitable for stable use of ultra-low latency and other additional functions. Even if the interface supports USB 3.0, there are cases where it can be used with USB 2.0 if the manufacturer announces such capabilities. Type-C is the same shape as a USB terminal. In many cases, the terminal on the audio interface side comes with a Type-C cable, and the terminal on the computer side comes with a Type-A cable, so be sure to check.

Thunderbolt

High-speed general-purpose data transmission technology jointly developed by Apple and Intel. The connection method is even faster than USB 3.0 and 3.1, and boasts a transfer speed 8 times faster than USB 3.0 and 5 times faster than USB 3.1. Many Thunderbolt terminals can be found on Mac computers, but there are a few Windows models available as well. Please note that there are three versions, Thunderbolt (1), Thunderbolt 2, and Thunderbolt 3, which may also be incompatible with other versions. The shape of the Thunderbolt 3 terminal is the same as USB Type-C, but the they are different standards, so it cannot be judged from the terminal shape alone. A Thunderbolt 3 audio interface does not work when connected to the USB Type-C port, so please check the manufacturer's information carefully.

Audio interface specifications and functions

Number of quantization bits, sampling frequency

In the specifications of audio interfaces, you will find something like "maximum 24bit / 192khz". In this case, "24bit" represents the number of quantization bits and "192khz" represents the sampling frequency.

The sampling frequency indicates how many times a signal fluctuation is processed per second when converting an analog signal to a digital signal. It is 44100 times at 44.1khz. Since it is processed 192000 times at 192khz, the sound is theoretically high definition.

The number of quantization bits indicates the amount of information at any instant. The analog signal has a smooth curve as shown in the figure below, but the digital signal is represented by "0" and "1", so the curve becomes stepped. The higher the number of quantization bits, the closer the staircase becomes to the natural curve. With 8bit, there are 256 steps, with 16bit there are 65,536 steps, and with 24bit there are 16,777,216 steps. If you listen carefully, you’ll find that there is a considerable difference in sound quality between 16bit and 24bit, but in reality it is not as overwhelming as the number appears. However, since there is a difference in dynamic range, etc., the larger the number of bits, the better in terms of noise suppression.

There are advantages to increasing the number of bits and sampling frequency, but there are also disadvantages such as a large file size and the load on the computer. You will have to balance them when selecting, but at first, there is no problem if you select 16bit or 24bit for the number of quantization bits and 44.1kHz, 48kHz, or 96kHz for the sampling frequency.

Loopback

This function allows you to record and distribute audio on your computer simultaneously. In normal streaming, for example, you input a voice into a microphone and only that sound is streamed. With a loopback function, sounds such as background music played on the computer can also be added to the stream, and it is possible to play background music in the background at the time of streaming, or to play a backing track from the computer and sing along. You can also send the sound of other applications to your DAW software for recording.

DSP

Abbreviation for Digital Signal Processor. It is possible to reduce the load on the computer by performing processing such as effects on the audio interface side. A typical example is UNIVERSAL AUDIO's Apollo series. The DSP built into the audio interface allows you to use high quality UAD plug-ins without overloading your computer. However, DSP also has various functions depending on the model. Since the range of things that can be done varies greatly depending on the model, such as those that can apply effects only to the sound of the signal being directly monitored and those that provide a variety of functions including meters using DSP, it is necessary to check each model individually and whether it will suit your needs.