Posted by Jerry Avins July 4, 2007
pal.debabrata123 wrote:
>> TKEO on DTMF is producing a sinusoidal signal, and amdf on this generated >> perhaps will give a constant local minima :-( I am still trying to do a >> narrowband detection cheaply. >> Can any body has already observed TKE0 on DTMF signal ? >> Regds, >> d.pal >> > As of today I have ended up with this strategy described below for > narrowband detection: > > 1) first square and low pass filter for envelope detection.
Linear envelope detection requires taking the absolute value, not the square. It only works well if the sample rate is several times the carrier frequency. ... Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Posted by pal.debabrata123 July 4, 2007
>TKEO on DTMF is producing a sinusoidal signal, and amdf on this generated >perhaps will give a constant local minima :-( I am still trying to do a >narrowband detection cheaply. >Can any body has already observed TKE0 on DTMF signal ? >Regds, >d.pal >
As of today I have ended up with this strategy described below for narrowband detection: 1) first square and low pass filter for envelope detection. 2) Do automatic gain control with reference to this envelope. 3) do a TKEO 4) calculate variance, if it it low and mean is a positive above a threshold, tone is detected! ( may be fax/modem/echo of dial tone) 5) do another TKEO on the above tkeo ! if positive with low variance it is a dtmf! Can anyone make a comment on this , about the potential algorithmic optimization wherever possible !
Posted by pal.debabrata123 July 3, 2007
TKEO on DTMF is producing a sinusoidal signal, and amdf on this generated
perhaps will give a constant local minima :-( I am still trying to do a
narrowband detection cheaply. 
Can any body has already observed TKE0 on DTMF signal ?
Regds,
d.pal