Forums

DTMF detection with Goertzel

Started by ma July 13, 2005
Roman Rumian wrote:
> Hi Jerry, > > Jerry Avins napisał(a): > (...) > >> >> I don't see that the tones have to persist. Whenever the complete set >> of tones is present, the state they prescribe is entered, That state >> persists until a valid countermand is detected. An on/off tone can be >> replaced with the transmission channel. A tone (or decoded set of >> three tones) on the one channel raises a flag; the same tone on the >> other lowers it. From your answer, I suspect that I'm overlooking a >> constraint or obvious simplification. Am I? > > > No. It seems resonable, but I am afraid, that have to send all 8 inputs > state simultaneously. What then ? > Serial transmission and then parallel buffer ? > > Best regards > > Roman
That's one way. Eight tones with the channel determining on/off is another. I can think of more, but none seems as good. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Hello Clay,

I have already finished ! :-)

Dsp implementation took one week.

I use 8 freqencies from 16.6 kHz to 19.8 kHz spaced 400Hz in both - left 
and right - audio channels, but complemented.

The problem is MPEG Audio coding used in communication channel, which do 
not tolerate weak tones, specially at low rates, but at 256kbps and 
-16dB  it works.

Best regards

Roman Rumian
"Roman Rumian" <usun_torumian@agh.edu.pl> wrote in message 
news:de46fs$91h$1@galaxy.uci.agh.edu.pl...
> Hello Clay, > > I have already finished ! :-) > > Dsp implementation took one week. > > I use 8 freqencies from 16.6 kHz to 19.8 kHz spaced 400Hz in both - left > and right - audio channels, but complemented. > > The problem is MPEG Audio coding used in communication channel, which do > not tolerate weak tones, specially at low rates, but at 256kbps and -16dB > it works. > > Best regards > > Roman Rumian
Excellent!! Clay
Hi here,

I want to detect "CAS(CPE Alerting Signal) Tone" with the Goertzel Algo
used in DTMF, is it OK?
I believe that CAS Tone is just a special DTMF Tone, comprised with two
frequency-2130Hz and 2750Hz. CAS Tone detection also has a more strict
aquirement than DTMF, such as accurate detection in hook-off and
hook-on.
2nd harmonic detection with 8k sampling to CAS Tone is not realistic,
as 2750Hz *2 is more than 4K. So I check (2130*0.5)Hz and (2750*0.5)Hz
to avoid CAS Tone is above frequencies' 2nd harmonic. Does it work?

Best Regards,
JIa

Hi here,

I want to detect "CAS(CPE Alerting Signal) Tone" with the Goertzel Algo
used in DTMF, is it OK?
I believe that CAS Tone is just a special DTMF Tone, comprised with two
frequency-2130Hz and 2750Hz. CAS Tone detection also has a more strict
aquirement than DTMF, such as accurate detection in hook-off and
hook-on.
2nd harmonic detection with 8k sampling to CAS Tone is not realistic,
as 2750Hz *2 is more than 4K. So I check (2130*0.5)Hz and (2750*0.5)Hz
to avoid CAS Tone is above frequencies' 2nd harmonic. Does it work?

Best Regards,
JIa

"jia" <jia.qinghua@gmail.com> wrote in message 
news:1126253700.629708.139380@z14g2000cwz.googlegroups.com...
> Hi here, > > I want to detect "CAS(CPE Alerting Signal) Tone" with the Goertzel Algo > used in DTMF, is it OK? > I believe that CAS Tone is just a special DTMF Tone, comprised with two > frequency-2130Hz and 2750Hz. CAS Tone detection also has a more strict > aquirement than DTMF, such as accurate detection in hook-off and > hook-on. > 2nd harmonic detection with 8k sampling to CAS Tone is not realistic, > as 2750Hz *2 is more than 4K. So I check (2130*0.5)Hz and (2750*0.5)Hz > to avoid CAS Tone is above frequencies' 2nd harmonic. Does it work? > > Best Regards, > JIa >
Hello JIa, Just use a purity check based on Parseval's (actually the special case known as Bessel's) relation to see if during the tone that nothing else is present. I.e., just compare the energy in the tone detectors to the total time domain energy. You don't need the 2nd harmonic detection this way. Clay
Hi, Clay

Thanks to your answer.

CAS Tone needs to be detected during off hook, i.e. present with voice
and others. So the detection is a little more difficult than that of
DTMF.  Someone said we can use the technology of "Voice Elimination",
but I suppose it is too complex.

Maybe we can  make use of  the characteristic of CAS Tone, i.e. Tone
During Time is 75-85ms.

Jia