[Asterisk-Users] Answering Machine Detection

[Steve Underwood]

Ray Burkholder wrote:

>Might want to write a new 
>  
>
>>"energy detector" algorithm in dsp.c though based on a wideband/low Q 
>>resonator approach (move the pole way in towards the origin) 
>>as opposed to 
>>narrow band goertzels (pole on the unit circle). More robust 
>>for this type 
>>of work.
>>    
>>
>
>Where does one go to learn this terminology and the math to implement it?
>
Apparantly not to this source. :-) A Goertzel filter finds one output 
bin of a DFT. Since the width of the bins in a DFT is directly related 
to the number of samples you include in a processed block, the width of 
the Goertzel is too. A Geortzel is as wide or as narrow as you want it 
to be. Oh, and k does not need to be an integer, unless you are trying 
to evaluate phase. That is a common misconception. There is a sliding 
window version of a Goertzel filter, but this has the same 
characteristics as the standard version, as it is just a trick for 
calculating a continuous stream of Goertzels efficiently.

Regards,
Steve