If you have ever researched the specifications of one of your microphones you probably came across the sensitivity of your device. It is usually written as “x” mV @ 94 dB SPL / 1 Pa. ( “x” being an arbitrary value, Pa or Pascal being a unit of measure for pressure). What that means is that for a certain acoustical pressure of 1 Pa or 94 dB SPL your microphone will output “x” mV. For example, one of the most popular all-purpose microphone, the Shure SM58, has a sensitivity of 1.85 mV @ 94 dB SPL.
Most microphones output a maximum of around 30-40 mV. (millivolts) The standard professional recording level is +4 dBu which converted to volts is 1.228 V. So let’s compare the reference output level of the SM58 to the standard recording level – the difference is huge as the standard +4 dBu recording level is 663.8 times higher than the reference output of the SM58! To get that very low signal to a line level appropriate for recording, a microphone preamp is needed.
Why Not Just Use An Audio Interface?
To put it simply, an audio interface usually does three things – it uses its internal mic preamps to boost the signals to line level, it takes care of the A/D – D/A conversion and it creates the bridge to send and receive digital audio to and respectively from a computer. This makes an interface ideal for home studios but the fact that it does all these and it usually costs little money raises the question of how good is it at accomplishing all the above mentioned tasks?
In a nutshell, most consumer audio interfaces do a very decent job at accomplishing all those tasks all while giving you options for multiple inputs and outputs. Microphone preamps do only one thing – they boost a low mic level to line level. If you have an audio interface and you are happy with it and at the same time you are unsure whether you should buy a mic preamp then you do not need a mic preamp.
If you are trying to upgrade your home studio and you are looking for ways to enhance the quality of your recordings than investing in a mic preamp is probably worth it. (given that you already have some quality microphones)
Sonic Qualities of Mic Preamps
So, you decide to invest in a mic preamp in order to get better quality recordings – but do you want your preamp to be transparent or to add coloration? Why do some add coloration and why is it desirable?
To explain this in depth is beyond the scope of the article but per short coloration actually means distortion. (as distortion is any modification in frequency content or phase that a signal processing device projects upon a signal) Why would you want distortion in your recordings? Well the warmth and quality of vintage consoles and preamps all come from distortion/ coloration. This kind of “warm” coloration is usually 2nd harmonic distortion which sounds very pleasant to the human ear.
Preamps fall in two broad categories – transparent/ neutral and colorful/ enhancing. Deciding which one of these is desirable for your setup is more of a creative choice and neither is wrong.
How To Connect A Mic Preamp To Pro Tools
You have to take into consideration that most mic preamps do not have an analog to digital converter installed so you cannot connect them directly to your computer and Pro Tools and you will need either an analog to digital converter that connects to your computer or an audio interface that has an analog to digital converter that connects to your computer.
Also, to complicate things even more, most A/D converters do not have a standard connection like USB, FireWire or Thunderbolt so you cannot connect them directly to your computer unless you have some sort of PCIe card that has digital inputs such as MADI or ADAT Lightpipe or another I/O interface like the Pro Tools HD I/O. (Altough, if you do have one of these, you probably would not be reading this article.)
Best Budget Microphone Preamps Available Today
Enough theory crafting – let’s take a look at some of the coolest budget mic preamps on the market. We will look at some single input preamps and at some that boast up to eight inputs. Let’s dive in:
ART Tube MP
This tiny, nifty unit features a 12AX7A tube, a phase reverse switch, XLR (balanced) and jack (unbalanced) inputs and outputs, a 48V phantom power switch, and can also be used as a direct injection box. It is one of those bang for the buck deals – you get incredibly quiet amplification with a bit of tube character but overall transparent sound and it fits in your palm. Do not expect the tube character to be too pronounced, it is actually barely noticeable.
Click here to see reviews and prices for the ART Tube MP on Amazon.com
DBX 286 S
This one is actually more than just a single mic preamp, a lot more! In fact it is a whole channel strip as it features a de-esser with a tunable frequency, a classic DBX compressor, an enhancer and an expander/ gate. And the cool thing is that they all sound pretty great. Of course you do not necessarily have to use the processing if you do not want to as you can bypass it. Another great feature is the high pass filter that is right next to the amplification gain of this very transparent and great sounding mic preamp.
Click here to see reviews and prices for the DBX 286 S on Amazon.com
Presonus BlueTube V2
This mic preamp enables you to amplify two separate mics or use it as a stereo mic setup preamp. Beyond its cool looking VU meters you get a lot in a small package – : Class A XMAX mic preamps with 80 dB gain amplification, 12AX7 tube, Tube Drive control to dial in the amount of tube character, +48V phantom power and phase reversal switch, 80 Hz high-pass filter and -20 dB pad to reduce hot input levels. The only drawback to this unit is the vacuum tube that it ships with – you will do yourself a huge favor if you replace it with something better.
Click here to see reviews and prices for the Presonus BlueTube V2 on Amazon.com
Focusrite OctoPre MKII
I am sure the name Focusrite rings a bell for you – they are big players in the preamp and audio interface manufacturing industry and this unit is one of the reasons why. With this unit you get amazing signal to noise ratio, highly transparent Focusrite preamps, eight of them to be precise. It sports and A/D converter that can send out 8 channels of 96 kHz/ 24 bit digital audio through two ADAT outputs. It also allows for both internal and external clocking. The people at Focusrite say that the unit is optimized for drum tracking but I would say that it is optimized for all kinds of tracking.
Click here to see reviews and prices for the Focusrite OctoPre MKII on Amazon.com
Focusrite ISA One
This unit is for those of you who are quite serious about recording music. One channel featuring the infamous ISA preamp that is based on the ISA 110. It sports a mic/line/instrument input, an insert, a line/DI output, an impedance switch, a headphones output with level control, a VU meter, a hi-pass filter, +48V power and an optional 192kHz A/D converter that can connect via ADAT or S/PDIF to a PCIe card or audio interface. This is pristine quality in a box.
Click here to see reviews and prices for the Focusrite ISA One on Amazon.com
These are some of the cool options I used and loved that can be considered “budget” options. There are a lot of amazing products out there and we are lucky enough to be living in these times where audio equipment is incredibly cheap. (compared to how much something like the ISA costed 20 years ago) I recommend doing extensive research of any product your consider buying.