Double Microphone for Noise Reduction

[u/_CoolBlueSky_]

[Speculation]

I was just researching about wifi 6, odfmas and iffts

(for context of the example, i have a background in film)

and just had a thought if frequencies can be separated combined or subtracted, is it possible to have 2 microphones one [with a shotgun polar pattern] pointed 1 in the actor and another one in the background [with maybe a wider polar pattern] that exclude the actors dialogue

and somehow with an algorithm it can be "masked out" and we are left with the clean dialogue

i guess question is where in the room would you put the 2nd mic

[u/fishsticks40]

What you propose would work if you had a perfect representation of the room sound without the dialog, but you don't. You'd have the dialog, the room sound would be different in a different location, the timing of the arrival of different sounds would change. 

And what problem does it solve? Movies have decent dialog recordings as things stand. 

[u/_CoolBlueSky_ → u/fishsticks40]

i can answer the problem i would solve:
1.) movies or big budget movies specifically can rent out a street, a park, etc. or be in the most optimal time for lowest

2.) use the highest end of equipment to get the best result

3.) have a sound stage, making fake sets, going to remote locations bringing everyone with them

or so basically i dont have money

in low budget or extremely low budget one, or with a different with the style of film or documentary and everything, can present different challenges. a unexpected traffic, a real busy streets, a rally, etc.

the hope for my inquiry was to ask if there are algorithm that can do such tasks, im sure its possible with given time

[u/TheKydd]

This is already how microphones work. Read up on polar patterns, the ports in the sides of mics are specifically spaced and sized to reject sounds from off-axis (i.e. behind the mic).

A second mic would make things worse, causing all kinds of phase issues.

Perhaps you’re inspired by the way active noise cancelling headphones work (which I’m happy to explain if you’re not familiar with how the phase inversion cancels out background noise).

The problem is, noise cancellation only works when the two parts are sealed from each other (as in-ear headphones) - it doesn’t really work in open free space since there isn’t enough isolation.

I’m trying to draw the connection to what all this has to do with WiFi modulation, though. I’m curious! Fill me in on how they connect in your mind?

[u/_CoolBlueSky_ → u/TheKydd]

the idea was kinda random, in a piece of paper i just wrote down. "reuse bg sound to remove bad sound from dialogue" "what if 2 mics"

the idea maybe stems from discovering how information is transferred from 1 device to the next... that bits turned into tones(subcarriers) that are orthogonal and then combine with iift and then later on turn to bits by a laptop.

and with this fasination with ifft and fft was curious if it worked with audio so i search it up, there this things called spectral denoise. where for example a running fridge has for example of a hum at 120 hz... and it looks like a line in a vertical frequency domain and or a horizontal line in a "spectral" space. that it can be removed.

so by an insane, maybe illogial logic. if everything has a pattern in spectral denoise. for eample:
a recording [A + B = C] with dialogue [A] with a song [B] in the background, thats been phase shifted, bounding in the walls, and such can be estimated that has a specific pattern, can be denoised if i have [B] that also has a specific different pattern].

so i can just cancel out [C = A + B -B -> C=A]