What is a preamplifier?
A preamplifier (preamp) is a device used to take a microphone or instrument level signal, and increase the signal to a line level signal. Generally, we want things to be at a line level signal when we record them. Preamps universally have a few different features/settings on them:
Gain is the main amplifying feature of a preamp. When you hook up a microphone or instrument to a preamp, you increase the gain of the preamp to amplify the microphone-level or instrument-level signal.
Phantom Power, sometimes referred to as +48V is a matter of powering condenser microphones.
Instrument/Mic/Line Input Switches – Most audio interfaces these days have combo jacks that you can plug a microphone, instrument or line level source into via an XLR or ¼” cable. A microphone level signal is lower than an instrument level signal which is lower than a line level signal.Toggling the switch to “microphone”, will apply more gain to your circuit than “instrument” will. Selecting “Line” bypasses any gain from the preamp being applied to the input signal. Generally, as you move up in price, the quality and quantity of these inputs on an interface increases.
How does audio get in and out?
In order to record audio digitally, you first connect the output of your microphone, instrument or other gear to an input in your audio interface. Once the electrical signal enters the analog inputs on your interface and is amplified, it needs to be translated into 1’s and 0’s (binary) so that the sound information can be recorded and manipulated in your computer. Enter the analog to digital converter. An analog to digital converter (ADC) takes the electrical signal from your microphone, instrument or external gear and converts it into a digital representation that your computer can understand.
Now your audio is in your computer and you’re ready to listen back to it. You need something that takes those 1’s and 0’s (the digital representation of your audio) and translates them back into the analog world of electricity. A digital to analog converter (DAC) does just that. It converts the digital signals in your computer into electrical signals and sends them out to your speakers, headphones or outboard gear via an output on your audio interface.
To make a long story short, the better your converters are, the better the representation of the audio you can capture and reproduce in the ADC/DAC process. The quality of converters is one of the big factors that differentiates a $100 audio interface from a $10,000 audio interface.
The simplest of audio interfaces have only one set of analog stereo audio outputs that are meant to send line-level audio to your speakers. Generally these outputs are either ¼” balanced TRS or balanced XLR connections, but sometimes can be unbalanced RCA jacks. Generally, as you move up in price, the quality and quantity of these outputs on an interface increases.
On bigger audio interfaces, more audio outputs are generally included to allow for more advanced routing of audio to external devices like EQs, compressors, gates, exciters and more. These are especially helpful for routing and processing audio in external gear after you’ve already recorded or manipulated it digitally in your computer.
Digital outputs such as S/PDIF and ADAT are also included on larger and higher-end audio interfaces. These digital outputs allow you to send audio in and out of external devices without converting them back into an analog signal, thus preserving the original quality of the signal. The other benefit of these digital inputs and outputs is that you can send multiple channels of audio using only one cable, which can certainly simplify your setup.
The last type of outputs you generally see on audio interfaces are headphone outputs. These are either ¼” or ⅛” TRS outputs designed to allow you to plug your headphones directly into them. The quality and quantity of these headphone outputs/amplifiers tends to increase as the price and size of the interface increases.
Now that you understand the basic components of an audio interface, you’re ready to start choosing the right one for you. It can be a complicated process, and the “right” audio interface for you all depends on the type of audio work you do. Luckily, our whole team of audio experts is here to help! You can get in touch with one of us by phone (301-946-8808), email ([email protected]), or live chat at www.chucklevins.com.