[Asterisk-Users] Bounty! For help with echo cancellation code.

[echo-asterisk at secondphone.com]

On Wed, Jul 14, 2004 at 10:14:19AM -0700, Bob Knight wrote:
> echo-asterisk at secondphone.com wrote:
> >>>From the CLI and during a call I want to be able to:
> >
> >  *** Pulse the outgoing line and record at least 50 ms of the incoming 
> >  line.
> >
> >      The pulse waveform must be specifiable as a series of amplitudes
> >      for each 1/8000 sec time slot.  It would be best of these values
> >      could be read from a file specified on the CLI command line.
> >
> >      Timing should be synced between the pulse and the echo so that the
> >      delay from the pulse to the echo can be accurately determined.
> >
> >      Echo cancellation should be disabled during this operation.
> >
> >      This would operate similar to the echo-training code that operates
> >      at the initiation of a call except that this could be done at
> >      any time.
> >
> >      The initial pulse and any echoes can be combined and saved in a
> >      single channel.
> >
> >      Output should go to a file and should be in a simple format that
> >      a program such as Audacity can read, display and play. 
> >       
> >
> >  *** Pulse the outgoing line and record at least 50 ms of the incoming 
> >  line.
> >
> >      Same as above EXCEPT echo cancellation would not be disabled during
> >      this test and the results of the echo cancellation operations should
> >      be recorded and saved in a separate channel.
> >      
> >
> >  *** Change variables used to control echo cancellation.
> >
> >      Only the code in mec2.h is of interest.
> >   
> >      I will help identify the variables and modify the mec2.h code as
> >      needed to accomplish this goal.
> >
> >      There are a lot of parameters in mec2.h that may affect the quality
> >      of the echo cancellation.  I want to be able to adjust them 'on the
> >      fly' and be able to immediately hear the results.
> >
> >
> >I am open to alternative proposals which would accomplish the same goals.
> >
> >Name your price.
> 
> How about being able to "see" the results real time?
> I use a package called SMAART from siasoft.com.
> It is a dual channel spectrum analyzer.
> Run the output line as your reference channel
> and the input line as your measurement channel.
> 
> You can get great info from the impulse response
> and transfer function.
> 
> You could also use this to compare different codecs.
> The impulse function will tell you how long it takes.
> The transfer function will tell you just how good a
> job it did at reconstruction the original audio.
> 

Almost 20 years ago I wrote my own digital spectrum analyzer code
which I then used to do my research.  Provided that SMAART can fully
utilize the transfer function (do convolutions etc) it would may be
useful, but spectrum analysis is not the hard part.  Controlling and
getting the data out of zaptel.o is the hard part and help with that
is what is requested in the Bounty!

echo



> -- 
> Bob Knight
> [-w] the work option
> bk at minusw.com
> 925-449-9163
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