DTMF detection and samples

Hi. I�m a newbie in this but I need to acomplish a job with this stuff. I�m
capturing sound through the sound blaster and then need to detect if there
were some DTMF. For this I�m using Goertzel. What I can�t understand is
about buffering and samples, I mean: Do I have to run the goertzel for
N=106 on each sample and sum all the results and then try to detect if
there were DTMF or this is processing each sample?. I�m processing only
one sample and the results are wrong, meaning I press 1 and it detects *,
and so.

Thanks in advance 

dkurman wrote:
> Hi. I�m a newbie in this but I need to acomplish a job with this stuff. I�m
> capturing sound through the sound blaster and then need to detect if there
> were some DTMF. For this I�m using Goertzel. What I can�t understand is
> about buffering and samples, I mean: Do I have to run the goertzel for
> N=106 on each sample and sum all the results and then try to detect if
> there were DTMF or this is processing each sample?. I�m processing only
> one sample and the results are wrong, meaning I press 1 and it detects *,
> and so.
> 
> Thanks in advance 
> 

You only need to run the Goertzel transform once per N samples, but you 
have to run it on all N of them.  The result is invalid until the Nth 
sample though, so if you're doing your processing one sample at a time, 
only the Nth output is valid.  Note that because of this, you can skip 
the feed-forward on all but the last sample.

Once you've reached N, you'll need to reset the delay lines and start 
working on the next N samples.  Failure to do this will yeild invalid 
results.

-- 
Jim Thomas            Principal Applications Engineer  Bittware, Inc
jthomas@bittware.com  http://www.bittware.com    (603) 226-0404 x536
Getting an inch of snow is like winning ten cents in the lottery - Calvin

Thanks. This is the part I understand. The one I can�t get is about reading
the samples, I mean, I can read N bytes from buffer, but puting it in a
Byte array, so each sample will be of 1 byte(?). I need to read at least 4
samples of 2048 bytes each. I don�t know how to do this, but I think this
would be a language development forum question, isn�t it?

thanks again



>dkurman wrote:
>> Hi. I�m a newbie in this but I need to acomplish a job with this stuff.
I�m
>> capturing sound through the sound blaster and then need to detect if
there
>> were some DTMF. For this I�m using Goertzel. What I can�t understand
is
>> about buffering and samples, I mean: Do I have to run the goertzel for
>> N=106 on each sample and sum all the results and then try to detect if
>> there were DTMF or this is processing each sample?. I�m processing
only
>> one sample and the results are wrong, meaning I press 1 and it detects
*,
>> and so.
>> 
>> Thanks in advance 
>> 
>
>You only need to run the Goertzel transform once per N samples, but you 
>have to run it on all N of them.  The result is invalid until the Nth 
>sample though, so if you're doing your processing one sample at a time, 
>only the Nth output is valid.  Note that because of this, you can skip 
>the feed-forward on all but the last sample.
>
>Once you've reached N, you'll need to reset the delay lines and start 
>working on the next N samples.  Failure to do this will yeild invalid 
>results.
>
>-- 
>Jim Thomas            Principal Applications Engineer  Bittware, Inc
>jthomas@bittware.com  http://www.bittware.com    (603) 226-0404 x536
>Getting an inch of snow is like winning ten cents in the lottery -
Calvin
>