Re: DTMF detection with Goertzel

[Roman Rumian]

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

[Clay S. Turner]

"Roman Rumian" <[email protected]> wrote in message
news:[email protected]...
> 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

[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]

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

[Clay S. Turner]

"jia" <[email protected]> wrote in message
news:[email protected] oups.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

[jia]

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