"robert bristow-johnson" <rbj@audioimagination.com> wrote in message news:1190430764.428670.26300@o80g2000hse.googlegroups.com...> > > > > 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. >I have serious doubts about the feasibility. I tried something like that and it didn't work good. The problem is that the recording and the signal are weakly correllated, plus noise, plus the variations of the environment, plus the nonlinear distortion, plus misc. nonidealities, plus rate mismatch. If a recording is done as MP3, this makes for the complete disaster. So, I leave this method to the cinema scenarists. Vladimir Vassilevsky DSP and Mixed Signal Consultant www.abvolt.com
Noise Cancellation
Started by ●September 21, 2007
Reply by ●September 23, 20072007-09-23
Reply by ●September 23, 20072007-09-23
in a "hostile environment", yes, it won't be that easy... If the source is an FM station, they use heavy processing, neither linear nor time invariant. If the source is MP3, the "quantization noise floor" is just below the hearing threshold, and I think phase is quite muddled up too. It might still make an interesting lab exercise under controlled conditions, though.>> plus the nonlinear distortionThe good news is once LMS works I might be able to nail the nonlinear distortion at the same time, if I simply include time-delayed versions take x^2, x^3, x^4 ..., x being one signal. -mn
Reply by ●September 23, 20072007-09-23
Stacy wrote:> 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?In the movies, it's easy. TV, too. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●October 2, 20072007-10-02
See NoiseMuter, Compandent's excellent Adaptive Noise Canceler designed for enhancing speech in noisy environment: http://www.Compandent.com/products_anc.htm http://www.Compandent.com/NoiseMuterFactSheet.pdf Stacy 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.
