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Is ANC possible without microphones?

post #1 of 6
Thread Starter 

Dear reader,

 

For a study project I’m looking into the possibilities of ANC for DJ headphones. When studying ANC I was wondering if it’s possible to do it without the use of microphones. Here’s what I propose:

When DJ-ing there’s one channel for music that goes into the room and to your monitors. The other channel goes to your headphone to mix in the next song. With ANC in your headphones you are able to cancel out noise in order to hear the music in your headphones better. The concern with ANC is that it works best with regular patterns (engine sounds) and that the ANC interferes with other equipment (phones etc.) therefore it’s not very suitable for DJ-ing.  My question is whether it would be possible to send the signal that goes to the room (and monitors) directly to your headphones (via cable) and than have a DSP converting the sound to the opposite sound waves? Would this eliminate the need to recognize patterns in sound as is the case with normal ANC? And most important would it actually be better for DJ-ing than normal ANC (or PNC). 

 

I made a little illustration of the concept to make it more clear (hopefully).

(Circle is ANC, dashed line is proposed solution) (since I can't upload the image i put in this link-->) https://www.dropbox.com/s/19s6r7uubkws9om/Direct_ANC_Concept.jpg (all images are from TheNounProject)

 

Any feedback is welcome.

kind regards,

 

Pieter

The Netherlands

post #2 of 6
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post #3 of 6

The room itself will most likely alter you music signal too much for it to be canceled without the use of a microphone.  You would need to understand the transfer function of the room itself at your position if you wanted to cancel effectively.  For that you would need to employ a microphone to measure the music in the room and compare it to the dry signal coming from your source.  Overall output level in the room might be another problem.  Worth a shot though.

post #4 of 6

I'm not too familiar with the specifics of ANC, but here are two ideas to think about.

 

Calculate first reflection points in the room, and then use the time delay data to position your cancellation relative to the sound. See how well this works, and move from there. It will most definitely be extremely ineffective as ANC takes all of the rooms reflections into consideration.

 

A slightly better idea, would be to use an inverse of the impulse response of the room.

1. Walk into the gig, set your things up, take an impulse of the room. Account for the absorption of the audience.

2. Feed the currently playing track into the convolution reverb plugin and use the inverse as ANC.

 

I think this is a great idea actually! © Drew Hulva 2013

post #5 of 6
Thread Starter 

Thanks for the reply!

 

Coming back to your response, since the solution I'm looking for ideally should only be part of the headphone and no need for setups in advance of the gig, I was wondering if for this purpose just playing a 'negative' (not sure if this is the correct term) version of the track would be sufficient to cancel some of the noise. As I understood from DJ's, most of the noise comes from the monitors directed towards them, not so much from the room itself. The next question than would be, if by the proposed solution it would be possible to cancel out the monitors, does this mean that the sound of the room (the gig) will be heard or is this still masked by the monitors?

post #6 of 6

The correct term is inverted polarity.

 

The problem is that the signal will change quite a bit when it is converted to mechanical energy (loudspeaker), takes some time to travel to your ears (short delay but probably enough not to cancel high frequencies), room acoustics will change the sound too and the sound that arrives at your ears will change when you move even just a tiny bit.

 

Without a mic you will have a hard time getting high cancellation.

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