What is a Microphone Preamplifier?
To record any source with a computer, you have to convert it from analog to digital. Most computers do this internally at the sound card input. However, there are noise limits due to preamp amplification factors and 16-bit sample resolution that will restrict your mic’s performance before you even reach the A/D converter stage.
A Microphone Preamp overcomes these limiting factors by providing high impedance conversion to boost weak microphone level signals well above standard line levels (phono) which makes them suitable for direct connection into a sound card without the risk of overload distortion, but each time it must boost its own signal level. If not enough voltage is fed in by the preamp, distortion results as the internal voltages powering all stages are pushed beyond their design thresholds.
What is a Microphone Preamplifier?
A microphone preamplifier is an electronic device that first amplifies the electrical signal from a microphone. It is usually used to amplify signals from self-powered (active) microphones (such as condenser microphones).
The output of many line audio sources can also be fed through a mic preamp before further processing, such as signal compression or equalization. This is not to be confused with a control amplifier in high-fidelity reproduction equipment, which would instead provide a gain factor that can be used to boost the output of a stationary record player or another line-level source device.
A mic preamplifier should not be confused with an audio interface device commonly called a sound card, which also has a microphone input but is not intended for signal amplification, but rather to convert analog signals from a microphone to digital signals that can be processed by computer software.
In pro audio equipment, the terms “preamp”, “preamplifier” and “mic preamp” are used somewhat interchangeably to indicate a device between a microphone and a mixer’s line input. The terms can also refer to a stand-alone unit used in a sound reinforcement system, to a channel of a mixing console intended for microphones, or to equipment used in recording studios.
In recording studio terminology, “mic preamp” usually means a stand-alone unit near the microphone, while channel inputs on the mixing console are called “mic/line input channels”. In music production or live sound reinforcement, musical instruments are plugged into the console’s mic input channels.
The output from these channels is routed to a mixer’s “auxiliary send” bus. A condenser microphone typically has two stages of amplification in its internal preamplifier circuit, which may be active or passive depending on the type of circuitry used. The resulting low impedance output from the microphone may then be converted to a higher impedance signal by a line-level preamplifier. In some high-end recording equipment, this low impedance output is also available on the mixing console’s dedicated “mic input” channels.
The Output of the Microphone Preamplifier
As shown above, a microphone preamplifier is typically inserted into the signal chain between an audio mixer and an analog-to-digital converter (ADC) in order to boost the microphone’s weak output. A microphone can provide significant electrical noise, hum, or distortion if not properly amplified.
For very low power signals, a small amount of active gain is required to raise the level. Since a preamplifier’s output voltage must be able to swing a good deal further than its input, it needs a high current power supply and power amplifier stage. The microphone capsule may provide from 1 to 100 microvolts of the signal at 1 kilohm impedance. A typical preamplifier might require an additional 70 dB of gain in order to produce an output voltage capable of driving the ADC within the digital audio recorder.
The dynamic range of a microphone preamplifier is typically between 60 and 100 dB. The exact figure depends on the requirements of other parts in the system, particularly if other circuits are being driven. The “referred to input” dynamic range is the ratio of full-scale signal voltage (“V”) without any additional gain, to the residual noise at a specified bandwidth, with a microphone connected as the input.
In order to provide useful amplification from such a low source level, the preamplifier must have high open-loop gain and very low output impedance. It must also have a high common-mode rejection ratio (CMRR) so that the signal from the microphone is not affected by any noise in the system connected to its output.
A microphone preamplifier is often used immediately after a phantom power supply to provide improved performance when driving long cables or multiple microphones, as many microphone inputs don’t have enough power to directly drive a cable.
What is Gain?
This is typically 30 to 50 dB of amplification, with the amount depending on whether you are recording instruments or vocals. Instrument preamps may provide 60 to 70 dB of gain, while mic preamps only 20 to 30 dB because the much lower signal needed from a microphone reduces circuit noise that degrades sound quality. You can see why using a mic preamp adds significant noise when recording sensitive sources at low levels such as spoken word, especially under less than ideal conditions.
Do I need a Microphone Preamplifier?
This is probably the most important question you should ask yourself before buying one. The answer to this really depends on how serious about recording you are and what type of setup you’re planning on building. If your microphone will be plugged into an audio interface then there’s no need to get a preamp unless you’re going to be doing a lot of analog recording.
If you plan on recording directly onto your computer, I strongly recommend buying one because the microphone inputs found in most audio interfaces are not strong enough to properly deal with dynamic and condenser mics. The price should also play a big role when choosing a preamp. Some audio interfaces include a basic preamp, but most don’t. If you’re serious about recording then it’s important to have the best tools at your disposal so spending a little extra on a good mic pre is worth every penny.
Reasons Why Mic Preamps Matter
A mic preamp is a device that takes the low output from your microphone and amplifies it, so you can record at higher levels without distortion. At its most basic level, this makes sure whatever comes out sounds as good as possible since the noise was not present in any previous recording process due to lack of gain on their end before transmission through other devices such as interfaces or speakers, etc. Furthermore, by using high-quality components inside these circuits we are certain they will deliver cleaner signals with much more headroom which allows us greater flexibility when adjusting volume later down during mixing sessions if needed.
A good mic preamp will make your signal sound much clearer and less noisy. It sounds obvious, but in most cases, the ultimate goal should be to capture as transparently of a signature from what you’re playing as possible with this device- listen for yourself! Most budget models introduce hiss or background noise that doesn’t help any aspect of capturing natural tone; however high-end mic pres usually provide such clarity on their own without adding anything unwanted onto our end result (which can sometimes happen).
Mic preamps are essential for a range of engineers, from studio to live sound. There’s an amp modeler with 22 channels and EQ available in plugin format which will give you everything needed when mixing drums or guitars; whether you’re looking at two separate one-channel options that allow tweaks before recording begins or rack-mount multi-channel mic pres that can provide up 60dB gain reduction – there’s something here perfect just about any situation.
As a producer, you have the opportunity to affect how your track sounds. You can provide it with warmth or coolness by using different microphones and preamps for them; thinness through the use of acoustic guitars while thickening things up with synths in an attempt at creating contrast between those two instruments—just as painters sometimes mix watercolors on a palette knife before adding acrylics which create their desired effect(s). Experimenting will help guide future artistic decisions.
How do I choose a microphone preamp?
Crystal clear audio is pretty much the goal of every audio enthusiast out there. In order to achieve this, a quality microphone preamp is required. Of course, you can have a perfectly good recording setup with just a microphone and a digital recorder but if you’re looking for that extra touch or wish to record tracks on your PC or Mac then you might want to add a preamp into the mix.
So you’re looking to buy one of these magical boxes but are having trouble choosing between them? Here are some things you should consider when purchasing one:
- Price – Obviously, the price is an important factor when buying anything and mic preamps are no different. However, it’s important to remember that you shouldn’t just look at the cheapest option – check out all your options and find something within your budget range.
- Number of channels – If you’re planning on having multiple microphones then you will probably need a multi-channel mic preamp such as those with 2+ channels. If you only need 1 channel and won’t be recording more than one mic simultaneously then a single channel preamp will suffice.
These are the most common types of microphone preamps and they can be split into two categories depending on how many channels they have:
1 channel – For analog recorders, voiceovers, sending to the mixer or small studios with limited space.
2+ channels – For more advanced users, digital processing, larger home/project studios, and so on.
- A/D type – Your audio interface or digital recorder might already have an A/D converter built-in so it’s important to check this before buying. If not, look for an external preamp that has the same A/D type as your system. For example, if you’re using a Pro Tools|HD system then it’s important that your preamp and audio interface both support AES/EBU or S/PDIF input and output.
- Features – The more channels, features, and connections a preamp has, the higher its price tag. More advanced users should consider the number of features available to be important when buying a mic preamp, while beginners can get away with one that only has the most basic connections and functions.
- Interfaces – One of the most important things to consider when purchasing a microphone preamplifier is your audio interface. If you invest in a high-quality mic preamp, and then plug it into an entry-level audio interface, you’re not going to get good results. Mic pres require clean power to run properly — otherwise they can be noisy, with distortion. Before you purchase any mic preamp (or interface), make sure they’re compatible! You should also consider the connector type of your interface, as not all preamps are compatible with XLR connections. If you have an audio interface that only has a 3-pin connection for XLR cables, then don’t purchase a mic preamp that uses TRS or TS connectors3.
- Pad options – Another feature to look for is whether the preamplifier has a pad or not. Pad can help adjust input levels and prevent distortion. Equalizers inside of the microphone preamplifier can also help reduce background noise and interference, improving sound quality overall. There are models that come with multiple gain levels as well, which can make it easier to find the right level for every microphone. They come in various prices, so it’s also smart to look for ones that fit into any budget.
Types of Miccrophone Preamps
There are many different types of microphone preamps but they can be divided into three categories:
Preamps with a built-in ADC (analog to digital converter) – The output from this type of microphone preamp is an analog audio signal. These are typically greater for use with analog recorders, voiceovers, and similar applications.
Preamps without a built-in ADC – Analog to digital converters such as the ones found in these microphone preamps are typically built into the audio interface or digital recorder the preamp will be plugged into. These are great for recording directly onto your computer.
Preamps without a built-in ADC that can function as an outboard processor – The output from these types of mic preamps is either analog or digital depending on how it’s connected. The benefit of this is that you can use the same preamp for analog and digital recording setups.
If you wish to go analog, just connect your preamp to your mixer or audio interface. If you want to record digitally, then connect the preamps AES/EBU or S/PDIF output to either a digital recorder or audio interface with appropriate input. For example, if you have a Pro Tools|HD system with no internal ADC then you will need a preamp that has AES/EBU or S/PDIF output as well as a digital audio recorder with ADAT input.
Conclusion
Microphone preamplifiers are an important part of the recording process. Sound waves go through a microphone to capture noise and store it on a medium, like a tape or a hard drive. When you play them back, the sound needs to be amplified for proper listening. It is up to the microphone preamplifier to make sure this happens.
A microphone preamplifier also helps regulate gain levels for various kinds of microphones. Microphone inputs on most mixers are unbalanced, meaning the signal is received directly into the unit without any help from equalizers or processors built in to reduce background noise. This can result in weak sound levels and is one reason why studios use individual microphone preamplifiers.
A good microphone preamplifier is one of the most important parts of any recording studio. It changes sound waves coming in through a microphone into amplified electronic signals that can be played on speakers. Different inputs and types of preamplifiers can affect the kind of sound that comes out as well, making it important to find one that works for your recording style.
