Q: Can I use a low-pass filter to remove noise from my recording?

A question from an Audio Masterclass student...

I have a problem with acoustic noise in my recordings. I can hear most of the noise at high frequencies. Is it an acceptable solution to use a low-pass filter to filter it out?

The correct way to handle acoustic noise is to eliminate it at the source or insulate against it. A recording studio that charges $2000 a day is expected to have a quiet noise background.

Unfortunately it can cost a lot of money to protect against acoustic noise adequately and for many people a certain amount of noise is inevitable. (Note that noise from a computer is a common problem that we hear in students' work, which can be solved by not having the computer in the same room as the microphone.)

If there are still acoustic noise problems, then the following actions can be taken, but each creates a further problem...

• Position the sound source and microphone so that the microphone is pointing away from the noise
• Place the microphone closer to the sound source (you may not want a close-miked sound)
• Have the sound source play louder (you may not want this sound)
• Use a noise gate or edit out the noise (only works when the sound source is not playing)
• Use an expander (the action of the expander can be heard)
• Use a noise reduction plug-in (can work on speech, but can have significant side-effects on more complex sounds)
• Since noise is more audible at high frequencies, then filter the high frequencies (makes the sound dull)

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Anything you do to reduce the noise level other than eliminating it at the source or insulating against it will affect the signal. You will have to decide for yourself the best compromise between audible noise and degradation of the signal.