Comment by dharma1 | Hacker News Reader

Comment by dharma1 | Hacker News Reader

This isn't really a problem particular to drones. Most audio applications have noise issues - room reverb, wind noise, background chatter, preamp noise etc.

A couple of options spring to mind:

1) Get a noise fingerprint from the rotors and clean the audio with DSP. Hard because the noise of the rotors is constantly changing, but you could potentially place several contact mics next to the rotors and then subtract that from the main mic to get a cleaner signal

2) super directional audio with parabolic reflectors which reject audio outside the narrow beam

3) Don't record audio from the drone! Use wireless mics on the ground instead

Disclaimer: Used to be an audio engineer in past life and have been running a drone company for 3 years. We specialise in high end video (RED Epic), but are also working on some non-cinematography applications at the moment. We have both hardware and software teams. Any investors interested in hearing more, you can get in touch at info@londonhelicam.co.uk

Dharma,

Great points!

#1 - my thought was someone very clever could use the ESC output to the motors to estimate likely noise output from that rotor as well as measuring the actual noise output.

#2 I'm genuinely curious about the pros and cons of flying with a parabolic vs an array mic approach. It sounds like you could offer some insights here on a tradeoff.

#3 Well, yes. [grin] But that doesn't exactly solve the problem asked for.

I'll drop you an email now - thanks for responding! ^_^

Interesting David, myself and some of the guys at the office have been experimenting with quads lately and discussing possible military/police or media uses, after reading your initial proposal #1 struck me as a possible solution. However I've since swapped to another much more "back to basic principles" idea that while more difficult, would have a much wider impact.

Just to make sure I understand the problem ... wouldn't the simplest solution be a 5m audio cable hanging from the drone with a wind-shielded microphone at the bottom? I realize there are all kinds of dynamic problems with a setup like this, but 10dB of noise supression could be achieved easily like that.

It sounds like you're a perfect fit to solve this problem, if you were to choose to do so :-)

What about a set of software tuneable band reject filters instead of active noise reduction?

rotor noise tends to be really wide band, simple filtering won't be able to remove it

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