How to choose an audio interface

How does audio interface work

Audio interface takes care of converting analog signals to digital form that can be processed by a computer. The communication path can also be reversed. Audio interface can transform the digital audio from the computer into analog format. The sound can be therefore heard from the monitor speakers or through the headphones. If we tried to send an audio signal recording directly to your computer without an audio interface, the result would be miserable. Although the PC has a dedicated sound card, it does not allow quality conversion of signal from analog to digital. External sound card can also boost the incoming signal to the desired level, thanks to built-in preamplifier. The bottom line is that the internal sound card is suitable for playing the compressed sound but it isn't suitable for recording sound into computer.

Number of inputs on the audio interface

One of the top criteria when choosing an audio interface is the number of inputs. After all, there's a difference between recording one or several instruments at once. Audio interface with one input will suffice for recording vocals. A simple rule: number of inputs on the device must equal to to the number of instruments that you need to record simultaneously.

A special attention must be paid when recording electric guitar, bass guitar or keyboard. For these instruments we recommend choosing an audio interface capable of switching the input into the Hi-Z high impedance mode. This switch enable the flow of the maximal possible voltage without losses.

Another specialty is recording through a condenser microphone. This type of microphone offers a more authentic sound recording compared to other microphones but it requires a special 48 V supply, also called a phantom power. Most of the audio interfaces today have this feature.

Audio interface connectivity

USB Audio interface
The most common way to connect these devices. The main advantage is the compatibility with all common computers, laptops or portable devices.

FireWire Audio interface
More reliable type of connection when recording multiple channels. Used professionaly but not as good when talking compatibility. The everyday computer does not have a FirWire port.

Thunderbolt Audio interface
Professional interface, allowing reliable connection into multiple channels at once. This technical solution came out of joint effort of Intel and Apple and i is up to 8 times faster then USB.

PCIe Audio interface
It is installed directly onto the computer's motherboard and is highly professional. This device can avoid certain processes during data conversion, therefore there is almost no latency during the data processing.

Sampling frequency

The sampling frequency or sampling indicates how many samples are loaded per second during the transformation of the analog signal to a digital signal. The higher the number, the better the sound. CD recordings normally use frequency of 44.1 kHz. This standard is offered in the simplest USB soundcards, but higher tier interfaces can sample at a frequency up to 192 kHz. This criterion should not be a mantra, because the quality of the sound is influenced by other factors. Although, when simplified, one can say that recording in 96 kHz will sound better than the recording in 48 kHz, but the recording will take up to twice as much disk space in the computer. Professional studios are using equipment with a minimum sample rate of 44.1 kHz. Only the uppermost and lowermost part of the sound wave is used when the digital audio is converted back to analog sample. This means that the recording stored in the quality of 44.1 kHz can reproduce a frequency at around 22 kHz. Therefore still quite a bit more than the human ear is capable of hearing, with frequencies above 20 kHz no longer able to be simply heard.

Bit Depth

This criterion significantly affects the resulting sound dynamics. Simply put, the higher the number of bits of recording, the greater its dynamic range. CD standard is recorded in the quality of 16 bits. Since the 1-bit of recording corresponds to 6 dB dynamic range of recording, the dynamic range of the CD is 96 db. We must note the fact that part of this range will fall victim to electronic noise of the device and also the rest won't be stellar, because quieter passages will become louder. 24 bit audio quality is at a much higher level and is considered a minimum quality standard for professionals.

Summary

Audio interface is essential for any home space or rehearsal room in order to become a functional music studio. A recording software (DAW) and suitable cable for connecting the audio interface with computer, recorded instrument, microphone or headphones is a must for every master of sound.

Audio interface must be chosen according to ow many instruments will be recorded at once. A connectivity of a computer and laptop must be take into account as well. The most common and the most popular type is USB Audio interface.

The quality of the final product is also determined by the sampling frequency and bit depth. The minimum standard should be a device with 44,1 kHz frequency and 24-bit depth.