What Does The Damn Thing Actually Do And How Does This All Work? – Part 5: Preamps, Converters And Audio Interfaces

This is part 5 of our series of blog posts with simple explanations for the most common terms in audio, as well as features and functions found on recording studio equipment. The resource to end the confusion and help you focus on creating amazing music!

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Fellow audio nerds, please note:

The explanations are as non-technical and simple, as possible. I want it to be practical and useful and I don’t care if everything is 100% scientifically correct. All that matters to me are the results that the people who read this will hopefully get.

It’s not meant to be an academic piece of work on audio technology and if you are an experienced engineer who thinks this is stupid, then I’m really sorry, but this is not for you then. And I can definitely understand your desire for accuracy and your love for nerdy discussions, because I’m a total freak in this regard, myself (just ask my wife). I just think inflating our egos by throwing around complicated terms and definitions is not going to help anyone trying to capture a great song.

Preamps, Converters And Audio Interfaces

Preamp

A preamp (pre-amplifier) is a device that brings a low level microphone signal or instrument signal up to line level, which is the standard to send audio signals from one piece of gear to another. Basically every piece of audio gear, effects processor, etc. is designed to operate with line level signals. Since microphones and instruments produce very weak, low voltage signals, they have to be amplified to bring it up to line level.

So every interface, mixing console or other device that has a microphone input, has a microphone preamp built-in. Many people seem to believe that a preamp and an interface, for example, are to different things. But the fact is: If your interface has a mic input, it has a mic preamp. The mic input is your built-in mic preamp. If you want to use a more high quality, external mic preamp, you would have to plug it into a line input then, because the signal has already been amplified. Plugging on mic pre into another one doesn’t make much sense. Yet many people do that, because they don’t understand this. 

Mic Preamp

Brings mic signal up to line level signal. There are external, standalone mic preamps and the built-in preamps in interfaces, consoles, etc.

Instrument Preamp

Brings instrument signal up to line level signal. There are external, standalone instrument preamps and the built-in instrument preamps (“High-Z”) in interfaces, consoles, etc.

Line Preamp

A line input on a preamp can be used to plug in an already amplified line signal from another piece of gear into the preamp.

Converter

When we talk about converters, we mean devices that convert analog signals to digital signals and vice versa. Most audio interfaces have built in converters and there are external, high end converters, as well. Every piece of gear that has analog inputs or outputs (mic, line, high-z (instrument)) and some digital audio connection (USB, Firewire, Thunderbolt, PCI, AES, ADAT, SPDIF) at the same time, must have a converter built in.

D/A Conversion

Digital to analog. What comes out of your computer has to go through D/A conversion before it can be sent to speakers or other gear. 

A/D Conversion

Analog to Digital. What goes into your interface has to go through A/D conversion before it can be sent to your computer. 

Sample Rate

This defines how many samples of an analog signal are taken per second. The more samples per second, the more “accurate” the digital representation is and the higher the frequencies that can be represented.

Without going into the complicated, nerdy details, the rule of thumb is: If you want to reproduce a certain frequency in the digital world, the sample rate should be at least twice the frequency you want to reproduce. That’s why a minimum of 44,1kHz is used in pro audio. Humans can hear up to 20kHz, so if we want to reproduce the whole audible spectrum, we need to use a sample rate that’s at least 2 x 20kHz.

And as 48kHz is the video standard and video is so important these days, many people recommend recording at 48kHz, so you won’t have to convert for video afterwards.

Whether or not it makes a difference if you use 48kHz, 96kHz, 192kHz or even more is constantly being debated and there are pros and cons for all the different sample rates. I’d say, stick with 48kHz and just forget about it. You’ll be fine. It’s a high res, professional standard, it doesn’t take up as much CPU power and hard drive space as the higher sample rates and it’s already the right format for video.

It’s absolutely crucial that all your digital gear, interface, converters and software run at the same sample rate. So always double check that!

Bit Depth

You can probably set your software to 16, 24, or 32 Bit. And your interface/converters can probably convert analog signals to 16 Bit or 24 Bit digital signals. Just use the highest bit depth possible and you’re fine. 24 Bit and 32 Bit are both great, although 32 will probably just be used for the internal processing in your software. So, just record at 24 Bit. 16 is a bit problematic and there is basically no device nowadays that is limited to 16 Bit. So please double check every time you open up a session, that you are recording in at least 24 Bit. 

Clock

A clock is the device that keeps digital audio gear in sync. If you only use one digital device, such as the converters in your interface, or a digital mixing console, then it uses the internal clock. If you connect it to another piece of gear, you have to choose who the “master” is and who the “slave” is. This has to be defined, so both are being kept in sync by the same clock. 

Audio Interface

An audio interface is the device that sends all the various signals in your studio to your computer. So, it connects the “outside world” to your computer. When we say interface, we often talk about all-in-one devices, that you plug your mic etc. into. But the actual interface is just the part that connects the inputs and outputs of the converters to the computer via USB, Thunderbolt, PCI(e), or Firewire. So, an all-in-one audio interface usually consists of preamps, converters and the actual interface. 


These are the other posts in this series:

  • General Audio Terms

  • The Production Process

  • Routing And Processing

  • Microphones And Mic Accessories

  • ​Cables and Connectors

  • Computer, Software And Audio Files

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