Re: spandsp tone_detect.c goertzel perodogram

On Wed, 24 Oct 2007 12:00:33 +0000, Kamanashis wrote:

Hi,

Let me explain the situation, I am trying to differ beep from
different answering machine.
The information about the answering machine beep frequency is given
below.

[T-Mobile]
frequency=1250 ; frequency in Hz
energy=-30 ; energy in db
duration=250 ; duration in milisecond

[Verizon]
frequency=1500 ; frequency in Hz
energy=-20 ; energy in db
duration=550 ; duration in milisecond


[Sprint/Nextel]
frequency=1400 ; frequency in Hz
energy=-30 ; energy in db
;duration=600 ; duration in milisecond
duration=120 ; duration in milisecond

[AT&T/Cingular]
frequency=1700 ; frequency in Hz
energy=-20 ; energy in db
duration=300 ; duration in milisecond

I tried with goertzel algorithm (I used the implementation from
spandsp library).
It gave me farely close values of energy [T-Mobile], [Verizon] and
[Sprint/Nextel].
It was the [Sprint/Nextel] that I was testing. Then I tested Verizon.
I did not find a
way to detect the amds.

Now I have a few questions,

1. what does they mean by -20db and what is its relation with
goertzel energy.

The measure of energy (power, actually) is in relation to some reference,
so it should be dB(something). It's been a long time since I've done
phone stuff, so I couldn't tell if if it is dBV (volt), dBW (watt), dBm
(milliwatt), or some peculiar phone thing.

2. how can I use the periodogram functions of spandsp library, is
there any chance
that it may work for me ?

Dunno -- I'm not familiar with that library.

3. Is there any relation of duration of samples and goertzel
algorithm. (I get frames
of 20ms each, with 160 samples).

I'm not sure what you mean. Taking frames of 20ms each will spread the
spectrum of your signal, so it'll be difficult to tell what's going on to
an accuracy of more than 50Hz or so. It looks like your frequencies are
spaced widely enough that this won't be a big issue.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
.

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