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busy tone detect problem

Started by xingyu June 30, 2005
hi,all!
  i am working on a telephone program and i am new to DSP.i have search
all the resource about "busy tone detect" and find i can use 
"Goertzel algoritm".but i don't know how to deal with the result of the
"Goertzel",that is to say,i don't kown what is busy tone.so, can  any one
can give me the whole ideal for the process,or give you code about busy
tone detect?
thanks a lot!


		
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xingyu wrote:
> hi,all! > i am working on a telephone program and i am new to DSP.i have search > all the resource about "busy tone detect" and find i can use > "Goertzel algoritm".but i don't know how to deal with the result of the > "Goertzel",that is to say,i don't kown what is busy tone.so, can any one > can give me the whole ideal for the process,or give you code about busy > tone detect? > thanks a lot!
Busy tone is different from one country to the next. In the US, it consists of a 425 Hz tone chopped up with a cadence - that is, on for 0.5 seconds, off for 0.5 seconds. IIRC. It is similar to the congestion tone (aka fast busy) which uses the same frequencies, but a different cadence. There is an ITU spec that documents the call progress tones (frequencies and cadences) in most if not all countries, but I cannot remember which one it is. Q.35? These guys have some of the data online: http://www.hellosoft.com/products/hellovoice/cpt.htm Although the ITU would be a more authorative source and would include international tones as well. -- Jim Thomas Principal Applications Engineer Bittware, Inc jthomas@bittware.com http://www.bittware.com (603) 226-0404 x536 Any sufficiently advanced technology is indistinguishable from magic. - Arthur C. Clarke

"xingyu" <anan_fox@21cn.com> wrote in message 
news:Wv2dnbcphrmqnFnfRVn-pw@giganews.com...
> hi,all! > i am working on a telephone program and i am new to DSP.i have search > all the resource about "busy tone detect" and find i can use > "Goertzel algoritm".but i don't know how to deal with the result of the > "Goertzel",that is to say,i don't kown what is busy tone.so, can any one > can give me the whole ideal for the process,or give you code about busy > tone detect? > thanks a lot! > > > > This message was sent using the Comp.DSP web interface on > www.DSPRelated.com
The Goertzel is simply a very efficient band pass filter. You center it, based on certain coefficients, on to your frequency of interest. It simply kicks out a number that is representative of gain of that specific frequency. For example, you would want to center it on 425Hz, and based on your specific response time and detection certainties needs, you would write software to determine the validity of that signal. For example, looking for the characteristic 500ms on/off. Thomas
thanks!

		
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