A mic’s high‑pass filter isn’t just for removing rumbles.
I’m trying to figure out when to use the low‑pass and high‑pass filters on a microphone. Can you please offer me some advice?
SOS Forum post
SOS Editor In Chief Sam Inglis replies: Very few mics have low‑pass filters. If they do, it’s typically because the mic itself is inherently quite bright and the manufacturer wants to offer a more mellow, vintage voicing as an option. So you might engage the filter if what you were capturing was sounding harsh, scratchy or overly sibilant for example.
High‑pass filters are much more common and much more useful. They all cut low end from the signal that’s captured, but there are two basic use cases for this, which typically suit slightly different settings.
Sometimes you find yourself recording something that just naturally doesn’t have a lot of very low end. Examples might include female vocals, violin, ukulele and so on. In this case you can be pretty confident that anything you capture below 80Hz or so is going to be from an unwanted noise element, such as traffic going by or someone tapping their foot on the floor. So you might as well eliminate it at source using a high‑pass filter. Hence a lot of small‑diaphragm mics, for example, have relatively steep filters rolling off below 75 or 80 Hz.
The filter on the Neumann U87 is designed to compensate for proximity effect.
Other times, you find yourself miking sources quite close with a directional mic in such a way that the proximity effect is causing an unnatural or unwanted build‑up of low end. In this case what’s typically needed is a more gentle high‑pass filter with a much higher corner frequency. The filter on the Neumann U87, for example, is designed to compensate for proximity effect and I think turns over at 500Hz.