Most audio engineers know the purpose of a microphone preamplifier is to increase the gain of the mic. Beyond that basic task, mic preamps can color the sound and help skilled users create a signature sound. In this article, we’ll look deeper at microphone preamps and examine the many choices available today.
All microphone preamps take a very weak signal from a microphone and boost it to line level. From there, the signal goes to a console or other audio processing equipment in the chain. Each time an amplifier is used in the mic’s signal path, it called a gain stage. This amplification raises the volume of the signal to match the requirements of the next device in the chain. Of course, each gain stage introduces additional noise into the signal. Matching these gain stages is important to insuring a clean signal.
A key to using mic preamps correctly is to maintain the gain in the sweet spot. This means keeping the input gain just low enough to prevent the signal from clipping. Doing this helps maintain the signal level above the noise floor.
Probably the most critical component in the recording chain is the microphone. It is important to match the microphone to the type sound it is picking up. Microphones are like artist’s paint brushes. They can sound different on every voice and instrument. Certain mics are tried and true on a range of applications, while others are highly specialized. Also mic placement is important to how it sounds. Pick the microphone first and then match it to a preamp.
This is where preamps move from science to art. You can seek a clean, accurate, pristine sound. Or you can add flavor and color to your audio. Modern solid-state “clean” preamps boost sounds with minor harmonic distortion. This is what makes them “clean.” This uncolored — yet sterile — signal is a good choice when are doing additional processing with a DAW using plug-ins.
Vintage preamps are often celebrated for the color they bring to the signal. Their design really moves into the realm of art. These unique devices purposely use harmonic distortion to make the sound more enjoyable for listeners. They employ a range special electronic circuits or transformers to accomplish this. In the end, the harmonics add a unique signature to the audio. This is why there are so many preamps designed by such a diverse group of engineers.
Classic preamp designs go back many years. Many recordists have used these preamps to create classic hit records from the 1960s that have stood the test of time. These circuits are recreated in new hardware and plug-ins, while original vintage hardware continues to climb in value. Everyone recording wants lightning to strike again for their project and many believe the gear can help them do it.
In more modern times, channel strips outfitted with classic circuit designs have become popular. They help simplify the recording chain. Channel strips often contain high-end preamps, EQs, compressors and other components. They may be either in hardware or plug-in form. Each section of a channel strip conveys a unique character to the sound. Channel strips, especially high-end ones, offer a wide palette of sonic choices.
In purchasing a mic preamp, start by evaluating the number of needed channels. It can range from one channel to eight and beyond. It all depends on the user and the goal of the project. Then, with hardware, pick either solid-state or tube/FET components. Tube preamps offer color, while solid-state electronics are much cleaner. Plug-ins emulate the sound of the hardware and have gotten much better in recent times.
Make sure you have adequate gain for the type of microphones being used. Condenser mics are OK with 30dB–50dB of gain but low-output mics like passive dynamics and ribbon mics may require up to 75 dB of gain. If you choose a computer interface with lower gain, in-line amplifiers can be used to boost the output of dynamic and ribbon mics. Also, many manufacturers are now building active ribbon mics, which raises the gain to standard levels.
As with all pro audio gear, you get what you pay for. Inexpensive mic preamps can sound very good and offer high sonic quality. But more premium preamps make is easier to develop a signature sound. The choice is usually determined by the project and a realistic budget.
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