Forums

Noise Cancellation

Started by Stacy September 21, 2007
If you have a recording with people talking in a room and a radio playing
at the same time, how do you remove the sound of the radio?

I am aware of adaptive noise cancellation with LMS. However the noise
there is white noise or noise from an airplane cockpit, waterfall, etc.
On Fri, 21 Sep 2007 10:43:47 -0500, "Stacy"
<stacy2003_young@yahoo.com> wrote:

>If you have a recording with people talking in a room and a radio playing >at the same time, how do you remove the sound of the radio? > >I am aware of adaptive noise cancellation with LMS. However the noise >there is white noise or noise from an airplane cockpit, waterfall, etc.
You could get a clean recording of the radio programming and subtract it from the signal. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
Eric Jacobsen wrote:
> On Fri, 21 Sep 2007 10:43:47 -0500, "Stacy" > <stacy2003_young@yahoo.com> wrote: > >> If you have a recording with people talking in a room and a radio playing >> at the same time, how do you remove the sound of the radio? >> >> I am aware of adaptive noise cancellation with LMS. However the noise >> there is white noise or noise from an airplane cockpit, waterfall, etc. > > You could get a clean recording of the radio programming and subtract > it from the signal.
Provided you get the phase right. :-) Jerry -- Engineering is the art of making what you want from things you can get. &macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;
"Stacy" <stacy2003_young@yahoo.com> wrote in message 
news:apidnZnmJacue27bnZ2dnUVZ_vCknZ2d@giganews.com...
> If you have a recording with people talking in a room and a radio playing > at the same time, how do you remove the sound of the radio? > > I am aware of adaptive noise cancellation with LMS. However the noise > there is white noise or noise from an airplane cockpit, waterfall, etc.
Tom Stockham at Uof Utah?? long ago removed the orchestra from Caruso recordings using cepstral techniques. Maybe that would work for you depending on the location of the radio, the people/speakers, the microphone(s), multipath and the spectral differences of the two signals. Fred
On Sep 21, 2:42 pm, Jerry Avins <j...@ieee.org> wrote:
> Eric Jacobsen wrote: > > On Fri, 21 Sep 2007 10:43:47 -0500, "Stacy" > > <stacy2003_yo...@yahoo.com> wrote: > > >> If you have a recording with people talking in a room and a radio playing > >> at the same time, how do you remove the sound of the radio? > > >> I am aware of adaptive noise cancellation with LMS. However the noise > >> there is white noise or noise from an airplane cockpit, waterfall, etc. > > > You could get a clean recording of the radio programming and subtract > > it from the signal. > > Provided you get the phase right. :-)
the LMS alg is s'pose to take care of that, i think. r b-j
On Sep 22, 3:12 pm, robert bristow-johnson <r...@audioimagination.com>
wrote:
> On Sep 21, 2:42 pm, Jerry Avins <j...@ieee.org> wrote: > > > Eric Jacobsen wrote: > > > On Fri, 21 Sep 2007 10:43:47 -0500, "Stacy" > > > <stacy2003_yo...@yahoo.com> wrote: > > > >> If you have a recording with people talking in a room and a radio playing > > >> at the same time, how do you remove the sound of the radio? > > > >> I am aware of adaptive noise cancellation with LMS. However the noise > > >> there is white noise or noise from an airplane cockpit, waterfall, etc. > > > > You could get a clean recording of the radio programming and subtract > > > it from the signal. > > > Provided you get the phase right. :-) > > the LMS alg is s'pose to take care of that, i think. > > r b-j
It doesn't always work. Here's why. For the system to work we need good coherence between microphones. This means the mics must be reasonably close together.However, if they are too close you cancel the speech as well as the noise. Solution - put the mics a short distance apart and use a voice activity detector - algorithms based are this geometry are numerous. Fitlike
Let me state my question differently.

Mobsters will turn on a radio while they are in a room talking among
themselves. This is to distort what is being said in case the FBI is
making a recording. However, the FBI has techniques for removing most of
the radio from the recording so as to make the mobsters conversation
understandable.

Does anyone have an idea how this is done?

"Stacy" <stacy2003_young@yahoo.com> writes:

> Let me state my question differently. > > Mobsters will turn on a radio while they are in a room talking among > themselves. This is to distort what is being said in case the FBI is > making a recording. However, the FBI has techniques for removing most of > the radio from the recording so as to make the mobsters conversation > understandable. > > Does anyone have an idea how this is done?
These guys make this sort of product - maybe you can get some information there: http://www.dacaudio.com/ -- % Randy Yates % "She has an IQ of 1001, she has a jumpsuit %% Fuquay-Varina, NC % on, and she's also a telephone." %%% 919-577-9882 % %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO http://www.digitalsignallabs.com
On 22 Sep., 20:45, Randy Yates <ya...@ieee.org> wrote:
> "Stacy" <stacy2003_yo...@yahoo.com> writes: > > Let me state my question differently. > > > Mobsters will turn on a radio while they are in a room talking among > > themselves. This is to distort what is being said in case the FBI is > > making a recording. However, the FBI has techniques for removing most of > > the radio from the recording so as to make the mobsters conversation > > understandable. > > > Does anyone have an idea how this is done? > > These guys make this sort of product - maybe you can get some information > there: > > http://www.dacaudio.com/
They even have exact the same example (from the website) available as audio file: " Conversation masked by music radio interference. [After processing:] Music attenuated and speech clearer. (Noise reference separately recorded and used for cancellation) " Seems like a standard adaptive noise cancelling setup. If you can get hold of a recording of the station playing, you can use that as a reference for noise cancelling. Regards, Andor
One simple approach is as follows:
- Take a0 times the raw radio recording, align it with the received
signal
- plus a1 above signal time-shifted by one sample
- plus a2 the signal shifted by two samples
- etc etc
- until there are enough time-shifted versions to cover the impulse
response of the room with sufficient accuracy

- least-squares fit for a0..an
- scale the time-shifted signals with a0..an and add to signal

Effectively a0..an is the set of coefficients for a FIR filter.

This idea isn't too robust, though (like zero-forcing equalizer or simple
inverse filter)

-mn