#5202 NORM Future : Acoustic Tape Measure thinks I'm short!

[Zarro Boogs per Child]

#5202: Acoustic Tape Measure thinks I'm short!
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  Reporter:  cscott                     |       Owner:  bemasc        
      Type:  defect                     |      Status:  new           
  Priority:  normal                     |   Milestone:  Future Release
 Component:  acoustic-measure-activity  |     Version:                
Resolution:                             |    Keywords:                
  Verified:  0                          |  
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Comment(by bemasc):

 Replying to [comment:5 ohshima]:
 > Showing all measuremant is just an attempt to obscure the fact that this
 is not the best tool to measure the 1-2 meters distance.

 A meter stick would definitely be better, but I don't know if they will
 have meter sticks.  Maybe they can make some.

 > It just should be more explorable and explainable,

 I agree.  I am open to suggestions.  However, it is very difficult to do
 better than "look at the code".

 The activity relies on special autocorrelation properties of maximum
 length sequences produced by linear feedback shift registers.  It uses
 FFT-accelerated cross-correlations of these sequences to determine the
 time-delay between the two laptops.  There's also some very tricky timing
 logic required, because it is impossible to synchronize the clocks to
 sufficient accuracy over the network.  What I'm trying to say is, I have a
 degree in mathematical computer science, I wrote the program, and I still
 don't really understand why it works.  I have no idea how to explain it to
 a student, even an exceptionally bright 16-year-old.

 > and the UI should be simpler.

 How could the UI be any simpler?  It's got one button and one display
 field.

 > (Probably response time should be a slider to change the interval,
 though.)

 This might be a very good idea.  It would not be very difficult to add a
 slider to change the speed.  However, it would add complexity to the
 interface.  Alternatively, I have considered a system that automatically
 adjusts the speed depending on distance and background noise (the lower
 the SNR, and the longer the sequences must be to make correct
 measurements).

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Ticket URL: <http://dev.laptop.org/ticket/5202#comment:6>
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