3
$\begingroup$

It's a common problem that while talking with the another person on Smart phones with the help of regular headphones,we get very annoying sounds at background . The opposite person's voice gets mixed with full of such noise signals to such an extent that sometimes it becomes literally impossible to continue the conversation.

Which kind of noises could be possible in such situation?

Also,how do can we convert a regular (ordinary) headphone into a headphone which has ability cancel out or isolate these noise signals to a maximum extent while listening voice on headphones and make conversation noise free?

Note:please consider any practical situation of your choice like opposite person(person on other) side is in silence zone area and you are walking on the road or travelling by the car or you are also in the silence zone.

$\endgroup$
  • $\begingroup$ What is the source of the noise? Local, remote, thru the headphones or from the environment outside the headphones? $\endgroup$ – hotpaw2 May 4 '15 at 18:59
  • $\begingroup$ You can use a LMS or RLS adaptive filter if you have a separate channel where you can feed the noise signal. This document gives an example for LMS adaptive noise cancellation. $\endgroup$ – Naveen May 4 '15 at 19:30
  • $\begingroup$ @Naveen sir,please consider any practical situation of your choice like you are walking on the road or travelling by the car $\endgroup$ – sagar May 4 '15 at 19:51
  • $\begingroup$ Ok. The adaptive filter is mostly used for cancelling external noises from the environment(noise of train engine, other people talking etc). The principle is you use a second mic or sensor(apart from the one which you are talking into) which is also sufficiently isolated from your voice signal to capture the external noise. There are some external noises like Line Noise(60 Hz) due to interference from external AC sources which can be easily filter out using narrowband IIR notch filters. If you have a wireless headset, your bluetooth transmitter can also be a source of internal noise. $\endgroup$ – Naveen May 4 '15 at 20:25
  • $\begingroup$ you cannot use an adaptive filter in a headphone, the head movement will cause it to never adapt properly. no commercial headphone uses an adaptive system, maybe in a cockpit. $\endgroup$ – panthyon Jun 4 '15 at 23:35
1
$\begingroup$

here is a great website on building noise cancelling headphones http://headwize.com/?page_id=684

The concept behind noise cancelling headphones is simple. You listen to the environment and then play it back 180 degrees out of phase. When the original wave and the shifted wave meet, they cancel eachother out

enter image description here

The circuit is pretty simple. You have microphone go into an inverting amplifier, then you play it through the speaker (simplified version) This achieves noise cancellation.

edit

one major benefit of this solution is it is purely implemented in (analog) circuits. It doesn't require adaptive filtering, a decision engine, or any computing power. This type of circuit is what most commercial products use: Active filtering

Sometimes the solution to the problem isn't what we expected. We can get into signal estimation, adaptive filtering, DSP boards or MCUs, or any number of complex mathematically rigorous constructs but really, all that's needed is an inverting amplifier. If you want a software solution please state so (and in that even we can go back to signal estimation and adaptive filters) but since you asked for practical solutions to actually convert regular headphones I have presented a hardware implementation.

edit2

unfortunately the original website seems to have vanished, but here is the same exact content in a PDF I include the full article because it has parts lists, some helpful troubleshooting tips, and far more detail than I've included. And in case the new link breaks here is the main circuit with a brief explanation from pdf. The circuit itself looks complex but its really a 3 stage amplifier but one for each audio channel (left and right) so 6 amps total. As you can see the second stage is the inverting amp (makes signal 180 degrees out of phase) achieve our noise cancellation.

The following material is an excerpt from the noise cancellation headphone guide written by Jules Ryckebusch and all credit goes to Jules for design and explanation.

enter image description here

$\endgroup$
  • $\begingroup$ Why the downvotes? I directly address sagars question (in bold) how to convert regular headphones to noise canceling ones. THe website I linked has a full hardware implementation with schematics and pictures as well as advice on what components to buy and building the system. It really comes down to a simple inverting op amp circuit where the input is a microphone to capture ambient noise $\endgroup$ – andrew May 5 '15 at 16:33
  • $\begingroup$ but it doesn't. i've built these and it is dependent on the transfer functions of various relationships among components of the headphones. i can't say more for proprietary reasons $\endgroup$ – panthyon Jun 4 '15 at 23:34
  • $\begingroup$ I'll defer to your experience as I've never actually build them, just studied them. But just to clarify, when I say "it's just an inverting opamp" I'm not saying make an inverter and it will magically work. Its like me saying to build a small signal amplifier,(again) its just an inverting op-amp. There is still plenty of design work and math that goes on behind the scenes, my statement was just high level. $\endgroup$ – andrew Jun 5 '15 at 16:24
  • $\begingroup$ The signal consists of many frequencies. Which of the frequencies do you shift? Why do you cancel the signal out? Secondly, cannot you just attach your phones to the source of 0 signal, to the source of silence? It is much simpler circuitry. $\endgroup$ – Valentin Tihomirov Mar 31 '16 at 15:51
0
$\begingroup$

"Which kind of noises could be possible in such situation?" Noise cancelling seems to me to be an exercize in signal estimation. You need to estimate the external signal and send that estimated signal(180 degress out of phase) to the headphones I would think the noises that would best be cancelled are ones with good correlation in time. Totaly random noise sources would be very hard(or maybe impossible) to cancel since you couldn't accurately estimate them. A speaking voice may be hard to cancel but a constant sound like the roar of an airplane engine should be easier. Just my two cents, hope it helps

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.