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I am recording insect noise - buzzing, rustling in flowers, munching, etc. with a lav mic on a long skinny stick. My new goal is to remove ambient sound like planes, distant cars, etc.

Poor results (tons of ambient) so far with omnidirectional Audio Technica AT803B, which I had lying around. So switching to cardioid, something like a DPA 4080.

I'd like to record the insect with 1 mic and then ambient with a 2nd mic. Can I then use software like Audacity to subtract the sound in the 2nd mic from the 1st (since 1st won't have any insect sound), giving clean insect sound?

I saw a similar post, though it did not suggest this approach Noise reduction using multiple recordings of the same signal

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    $\begingroup$ It's pretty hard to record the insect sounds free of ambient noise without really good directional mics (like cardiod) but maybe you will need multiple mics (recording synchronously) focused on the same target insect and then with some pretty good audio processing, you would time-align the signal from the different mics so that the subject signal (the insect) teams up while the ambient would not team up. $\endgroup$ Aug 27, 2021 at 4:21
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    $\begingroup$ Look up LMS adaptive filtering. May come in handy here although it will be difficult to implement here. $\endgroup$
    – Ryan
    Aug 27, 2021 at 6:20

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Yes, it will work to some extent, but you're basically just making a directional mic out of two mics. If you make two recordings, it effectively allows you to adjust the polar pattern after the fact, though.

Use one directional mic facing the target, and one in the same location but facing the opposite direction (with its null end facing the insect), record both, and then subtract one from the other in post-production. You can adjust the relative mix of the two in post to null out the background noise as well as possible, so you're basically tweaking the polar pattern for each situation.

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    $\begingroup$ Great, spot on answer... A "natural"/immediate extension to that would be (conventional/delay-and-sum) beamforming. Or a, probably easier, approach could be MS, in order to "achieve" a "good" frontal lobe. Nice one, thanks. $\endgroup$
    – ZaellixA
    Jun 25 at 17:01
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First, in order to have a nice focus on the insect you want to record, it seems like you need a supercardioïd mic (though even with a narrow angle, you'll get ambient noises).

I think there are many plugins or software which do noise reducing, but I know one in particular, the ReaFIR plugin from Cockos(ReaFIR) based on Fast Fourier Transform. It's pretty easy to use and very efficient(in the limit of reasonable of course). It's provided with Reaper DAW which is free to use for 30 days and even more.

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  • $\begingroup$ Thanks so much. The Audacity forum is suggesting spectral-subtraction using the isolation tool or kn0ck0ut plugin (very old and unsupported). Does the ReaFIR plugin do something similar? Do you think it is worth switching to Reaper because it is better? I am familiar with Audacity. $\endgroup$
    – Nick Mirro
    Aug 29, 2021 at 6:33
  • $\begingroup$ Yes ReaFIR is based on spectral substraction. You have to read well the documentation before using it in order to have nice results, instead it could substract useful frequencies. I never used Audacity but Reaper is very good, I mainly use it for music production and never was disapointed (maybe you can find similar plugin on Audacity). $\endgroup$
    – terzan5
    Aug 29, 2021 at 9:43

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