I would like to do noise canceling that works in real time and does not allow microphones and computers to trace the canceled signal. Is it possible or is it useless to waste time as it is always possible to filter? Thanks

 

Describe in detail what you are trying to do. What is the source of the noise? Where do you want it cancelled — don’t say everywhere, because that is impossible.

As far as making it impossible to pick up on a microphone, how can that work? The noise cancelling circuit has to know what to cancel, which it does by using a microphone.

 

Describe in detail what you are trying to do. What is the source of the noise? Where do you want it cancelled — don’t say everywhere, because that is impossible.

As far as making it impossible to pick up on a microphone, how can that work? The noise cancelling circuit has to know what to cancel, which it does by using a microphone.

thanks for answered
must cancel sounds of the human body, for example the heartbeat, which cannot normally be heard by ear but which can be captured by a microphone and amplified

 

The quest is a bit nebulous, and I ask what is the more specific requirement? The not tracing part is a bit unclear..Where are the microphones and computers and where is the noise that they are not to trace???

 

The quest is a bit nebulous, and I ask what is the more specific requirement? The not tracing part is a bit unclear..Where are the microphones and computers and where is the noise that they are not to trace???

we propose the practical case that the microphones are connected to a computer and are located within a radius of 30/40 meters and the sound you want to cancel is the heartbeat. Is it possible to create an ANC system that prevents the computer from being able to trace the heart sound?

 

Do you have evidence that a microphone 30 or 40 meters away can record a human heartbeat? I would be very surprised if it could, and certainly not with typical background noise.

 

I don't think you really understand the principal of noise cancellation. The sound can only be cancelled right at the location where it is to be detected, i.e. at the microphone on the computer that you mention. Then a 180 degrees out of phase signal is generated at that point to cancel it. You can not generate an out of phase signal close to the source of the sound to stop it from being detected from any direction. Interference products between the two sounds will be radiated and will be frequency related.

 

So is the intention to cancel out the sound of a specific heartbeat, that would be picked up by a microphone about 100 feet away from it?? Unless the intent is to hide from an incredibly sensitive security system, I am wondering about what sort of microphone is that sensitive. Normal breathing is much louder than a human heartbeat. A more effective scheme would be to create the acoustic signature of a similar heartbeat to mask the one needing to avoid detection.

 

Is someone recording your heartbeat from 30 to 40 meters away?

 

I don't think you really understand the principal of noise cancellation. The sound can only be cancelled right at the location where it is to be detected, i.e. at the microphone on the computer that you mention. Then a 180 degrees out of phase signal is generated at that point to cancel it.

You can not generate an out of phase signal close to the source of the sound to stop it from being detected from any direction

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Exactly, I need this! Are you sure it really can't be done? because in this video the source of the signal generating destructive interference is placed close to the source of the signal to be canceled.

 

A heartbeat is at a very low frequency, use a highpass filter to block it.
But at 30m to 40m away it will not be detected anyway.

 

Exactly, I need this! Are you sure it really can't be done? because in this video the source of the signal generating destructive interference is placed close to the source of the signal to be canceled.

Yes, I am sure!
You should do a little research of your own before you start your next project. The "muzo" is a scam. Don't believe anything you see on youtube without checking it first.
https://red-dot-geek.com/muzo-review/

 

Certainly with two phase controlled sources a signal could be nulled at one very small point, in area with no reflective surfaces and no other sounds and no air currents. The area with cancellation will be VERY SMALL and if anything moves it would instantly vanish.
So, in a theoretical, anechoic, silent situation it could possibly be done, but much less likely in the real world. Maybe in some physics book?

 

we propose the practical case that the microphones are connected to a computer and are located within a radius of 30/40 meters and the sound you want to cancel is the heartbeat. Is it possible to create an ANC system that prevents the computer from being able to trace the heart sound?

Hi,

Oh absolutely! And the name of that ANC system is AirAndDistance.
Sound decreases with distance and the air in the room or outside dampens it as it travels. That means it would be hard to hear a heartbeat even 1 meter away. It may be impossible but with special sensors and amplifiers you can do an EKG.

However, it is not impossible to detect a heartbeat up to 20 meters away, but not by sound, by the movement through the clothing of the person. That would involve an optical detection system not audio I believe. Small movements of the skin under clothing can be detected and those movements are unique to a particular person.
From what I understand the military had this developed for identity checking of a possible human target so they get the right person and not an innocent bystander.

 

So the bottom line is that it is not presently possible to hear a heartbeat at any reasonable distance, especially without being rather obvious about it. And as for sensing it optically by looking at clothes motion, That is much harder to believe. I have thought a bit about large diaphram microphones for some interesting applications, but I no longer have access to the resources to fabricate them. And the market for microphones with good response below one Hz is quite small.

 

So the bottom line is that it is not presently possible to hear a heartbeat at any reasonable distance, especially without being rather obvious about it. And as for sensing it optically by looking at clothes motion, That is much harder to believe. I have thought a bit about large diaphram microphones for some interesting applications, but I no longer have access to the resources to fabricate them. And the market for microphones with good response below one Hz is quite small.

Hi,

Yes hard to believe, and that's because it's actually 20 meters and it is through the clothing not the clothing itself, according to a better information source. It uses an infrared laser with a spot about the size of a quarter. It also takes 30 seconds to get a reading presently, so the person has to be still.
The accuracy is something like 95 percent. The basic technology is not new it's just now at a larger distance than before.
For more details, do a search on "Jetson".

 

Clearly that is not what he is talking about, since he is trying to prevent it by acoustic noise canceling. And the laser could easily blocked by any opaque material.

 

Clearly that is not what he is talking about, since he is trying to prevent it by acoustic noise canceling. And the laser could easily blocked by any opaque material.

Hi Bob,

I guess you did not read my previous reply.

He started by asking for an acoustic solution, but after we decided it would be impossible or very hard to do, I offered a note about another way of doing it. Also, if it turns out that the laser method gives us the only hope of doing it, then we have to live with any imperfections. Besides that, there are already imperfections even without blocking the beam, and obviously we have to live with those too. As mentioned previously, the subject has to be still for 30 seconds. That may be a lot to ask in some situations, but if there is no other way to do this then we at least have something that works some of the time rather than none of the time.
There could be other solutions but I do not know of any at the present time.

Acoustically I would go with a bandpass filter. That's a no brainer. But it's hard to believe anything like that would work right.
There are 'listening' devices that use a parabolic reflector in conjunction with the mike. You can hear other people's voices at a distance but not sure if you can hear something as subtle as a heartbeat. Some experimenting would certainly be in order. Maybe a very large reflector. Or, maybe an array of microphones each with their own reflector and with all the signals summed together. The bandpass would help reduce unwanted noise, but any banging or knocking or foot tapping could mess up the results.

After saying that, maybe it is time to usher in the DSP methods. That could distinguish different sounds by their instantaneous signal patterns as well as their overall envelope. That's probably the best hope for a solution.

 

I guess you did not read my previous reply.

He started by asking for an acoustic solution, but after we decided it would be impossible or very hard to do, I offered a note about another way of doing it.

No, you didn’t read the original question. He is not asking for a way to read the heartbeat, he is asking for a way to by someone from doing that by acoustic means. You answer is to a question that no one asked.

 

If the object is to avoid observation for the purpose of avoiding identification then whatever mechanism selected would need to be well disguised. It does not seem like an adequate IR laser system, with a detector could be adequately portable. So one fear has been shown to be pointless. But those same microphones will be fine for voice recognition, easy to do at 30 yards.