![]() ![]() Actually, I am rather surprised that it took this long. However, I knew that this would be appearing on other sources as a video that could be viewed outside of Windows. However, I will give MSNBC this - they didn't give Microsoft a free ride on this, they ribbed them pretty hard. But no matter what the real cause, there is the appearance that it was removed from the page because it was too embarrassing. Perhaps this was just a normal rotation of a video. Nor was it under Videos, nor anywhere else I could find it easily. OK, so maybe they've moved it off the front page, but it should still be on the Technology subsection, right? Then I went to call it to the attention of a third coworker - and the video was no longer on the front page of MSNBC. I called this to the attention of two of my coworkers, and we viewed the video - total elapsed time, maybe twenty minutes. I went to - and there it was, third on the list of videos on the main page. See for a diagram of the AEC or read Haykin's Adaptive Filter Theory if you're looking for a decent book on the subject.Ī friend of mine called me at work (since he knew that to access MSNBC's videos requires Internet Explorer, Windows Media 9 or better, and Flash, and I have neither IE nor WMP at home) and told me about this. AEC is also the reason why talking immediately when you pick up a mobile phone leaves an audible echo of your own voice: estimating the coefficients of the filter is still taking place at that point. If an ADSL modem would not cancel out its own sent signal at its receiver, the attainable speed would be several times less. It is used in every telephone and mobile phone there is and is crucial to ADSL. This is setup is called AEC or Acoustic Noise Cancellation. You then have the voice-only signal left. ![]() You estimate the coefficients of the filter and use the music signal after the "room filter" has been applied to substract from the microphone signal. What is done in practice and works extremely good, is modelling that "echo" as a filter (a FIR transversal filter, which is simply a delay line). If you simply subtract the two signals, you will still hear the music signal quite loudly. The music signal has travelled across the room before it reaches the microphone, giving it some reverberations (echo). The signal at the microphone is not just the music signal (called far-end signal) plus the mic signal (near-end signal). For those interested, merely subtracting the two signals doesn't work.
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