Hello

I'm very new to PD, but I used MAX/MSP a few years ago for a small project. Now I doing another small project and I think I might be able to use PD for this.

Here is roughly what I need to do
1. Load and play a wave file (shouldn't be too hard
-> This is a normal audio wave-file but it has a special signal embedded in it. The signal is really at tone that plays at a specific frequency (19.200 Hz).
2. I need to detect when this "tone" is on and when it is not. A "bang" when it is on would be perfect.
3. I will use the bang to set a data-pin on the parallel port to high. I don't expect this to be a big problem either. I think it has been done before? If I somehow can write directly to a memory address I'm sure it can be done.

So the big problem is step 2. Maybe FFT could be used for this? I think FFT looks very complicated and I have no idea where to start. Can somebody help me please? Please remember that I'm very new to this program and I don't know a lot about audio-signals, fft...

I should also mention that:

1. I expect the 19.200 Hz tone to appear very frequently - sometimes many times per second
2. I may sometimes only appear in the left or right side of the stereo-signal.
   
   Any help would be greatly appreciated

Yes I'm sorry about the 19.2/19,2 Hz/kHz confusion. You are right it's 19.2 KHz

I've have been looking at the bp. My start out point was the example file called "H02.bandpass.pd" which is located in doc/3.audio.examples

However it seems to work better with low frequencies. Maybe the setup you have been using is better than mine. If you still have the .pd file, I would very much like to see it. Maybe you could send it to me? My address is: gandalf@beatnik.dk

Thank's for your time!

I'm trying to make a free alternative to the decoder found here: decoder - It is too expensive for me and for a lot of other people, I think. I'm not trying to put them out of business, but to make an alternative for people who are willing to mess around with electronics and who can't afford a readymade decoder and glasses.

for 2: I have already had a look at the fiddle~ and bonk~ externs. They look promising, but I don't understand them well enough to actually use them.
The audio contains other sounds + the 19,2 KHz signal, so I guess the envelope follower is out.
I hadn't thought about filtering the signal, as you suggest. Maybe I can use that in conjunction with fiddle~ ?!