Yeah. that would subtract off  the um uh parts of the signal that were the aspects of the signal that were different between the close - talk and the distant. You know , so  so uh um I guess in most echo cancellation  Yeah , so you  Given that um  Yeah , so you 're trying to  So you 'd  There 's a  a distance between the close and the distant mikes so there 's a time delay there , and after the time delay , there 's these various reflections. And if you figure out well what 's the  there 's a  a least squares algorithm that adjusts itself  adjusts the weight so that you try to subtract  essentially to subtract off uh different uh  different reflections. Right ? So let 's take the simple case where you just had  you had some uh some delay in a satellite connection or something and then there 's a  there 's an echo. It comes back. And you want to adjust this filter so that it will maximally reduce the effect of this echo.
So that would mean like if you were listening to the data that was recorded on one of those. Uh , just the raw data , you would  you might hear kind of an echo ? And  and then this  noise cancellation would get
Well , I 'm  I 'm  I 'm saying  That 's a simplified version of what 's really happening.  What 's really happening is  Well , when I 'm talking to you right now , you 're getting the direct sound from my speech , but you 're also getting , uh , the indirect sound that 's bounced around the room a number of times. OK ? So now , if you um try to r you  To completely remove the effect of that is sort of impractical for a number of technical reasons , but I  but  not to try to completely remove it , that is , invert the  the room response , but just to try to uh uh eliminate some of the  the effect of some of the echos. Um , a number of people have done this so that , say , if you 're talking to a speakerphone , uh it makes it more like it would be , if you were talking right up to it. So this is sort of the st the straight - forward approach. You say I  I  I want to use this uh  this item but I want to subtract off various kinds of echos. So you construct a filter , and you have this  this filtered version uh of the speech um gets uh uh  gets subtracted off from the original speech. Then you try to  you try to minimize the energy in some sense. And so um  uh with some constraints.
Kind of a clean up thing , that