A microphone's frequency response chart can tell you a lot about which situations are appropriate for a given microphone and which situations are not.

In theory, frequency response charts are generated at the factory by testing the microphones in an anechoic chamber. An anechoic chamber is a specially constructed room just for audio testing. The idea here is to create a controlled atmosphere where each microphone can be tested equally, so the room is completely dead, without any form of sound reflection.







Generally, a speaker is set up in front of the microphone that is being tested and pink noise is played (pink noise is all frequencies with equal energy in every octave). The microphone is routed into a spectrum analyzer that measures the output and a Frequency Response Chart is produced.

The chart is usually over the 20 Hz to 20 kHz range, which is the range of human hearing. So, how do you read it?

The horizontal numbers in a microphone frequency response chart represent frequencies (again, usually over the 20 Hz to 20 kHz range) and the vertical numbers represents relative responses in dB (Decibels). As you look at a frequency chart, you can tell how a given microphone performs at certain frequencies.

How is this information helpful? Well, let's look at the famous Shure SM57's frequency chart


The frequency response of the SM57 makes it especially good for certain instruments such as a snare drum because the fundamental frequency of the snare resides in the 150Hz to 250Hz range – right where the SM57 Microphone Frequency Chart shows that the SM57 response is flat, or neutral.

In other words, at this frequency, what you hear going into the microphone is what you will tend to hear coming out – nothing more, nothing less.

The presence bump to the right of the chart is just where the frequency of the "snap" of the snare resides. In addition, its rolled off low end makes it great for de-accentuating the kick drum which is often very close in proximity. This combination is what most engineers are looking for in a great snare drum mic – the ability to capture the true sound of the snare, accentuate its snap and reject other instruments in close proximity.


This article was reprinted with the permission of music and pro audio retailer Sweetwater. You can sign up for free Sweetwater online publications here.