While checking out the tech specs for your microphone or interface, you may have noticed a value for the product'simpedance rating. Impedance can best be defined as the amount of resistance inherent in the electrical system. It is measured in Ohms, often symbolized with the Greek character for Omega: Ω.
The higher the impedance rating, the more resistance is being applied to the signal, thusly causing a weaker signal to be transmitted. While this topic reaches deep into electronics and signal processing, for most applications, impedance should be noted for two things:
- The impedance rating for your input source, such as a microphone.
- The impedance rating for you interface's input; for example, the two inputs on the front of a PreSonus AudioBox USB.
When it comes to microphones, there are generally three "classes" of impedance rating:
- Low Impedance (0-600 Ω)
- Medium Impedance (600-10,000 Ω)
- High Impedance (10,000+ Ω)
Most inexpensive, consumer-grade microphones are high impedance. This means that they require quite a bit of amplification for a proper signal to be captured. Devices like the PreSonus AudioBox USB, or other USB audio interfaces, have limited power compared to high-powered professional mixing consoles. Therefore, they may not be able to properly amplify high impedance mics to an acceptable level.
When considering purchasing a new microphone to use with your interface, you will want to make sure the impedance for the mic is lower than the impedance for your interface input. For instance, the AudioBox USB has a preamp impedance rating of 1200 Ω. Therefore, you would want to make sure you are using a mic with an output impedance rated below 1200 Ω.
Please check the impedance ratings for your interface and your mic before making any purchase. If the impedance for the mic is higher than for the input, a loss of signal strength will occur. To receive the best signal, a mic of half the impedance of the interface input is the optimal choice.