Sub Audio Frequency Doubler

A number of references and links to articles in various publications, doing what you describe above. A few obvious and simple changes will be needed to make these work at 20Hz.

SioL

Modifying a bat detector is not going to work well. A bat detector lets you know there is a bat, but still leaves you in the dark what the sound really is like.

Depends on what the OP wants.

Since you are so very interested in me: I have been involved in developing electronic circuits for many years. It has provided me with income for the past decade, so I guess I qualify as a professional.

"Nico Coesel"

What a deadshit.

Nico is really just another smug, PITA, wog pig.

.......... Phil

Its not just a "detector", I haven't seen all the designs listed, but at least the one from Elektor is a SSB mod/demod thingy, with headphones, simply put.

Its basically a pitch-changer, if you will. It might have a problem removing the carrier/sideband sufficiently since input sig. is so close to the carrier causing beat tone which could perhaps be filtered out. Its worth a try and easy as well with PCB artwork done by Elektor. They may even have PCB's to order.

I can look it up and e-mail it, if interest exists (I've got elektor CDs for last 8 or so years).

the one from

This will still garble the harmonic relations in the original signal. Imagine a musical C-E-G chord is being played. If you shift the frequency up using SSB techniques, the frequency difference between the tones will be absolute which will make the chord sound unrecognizeble as a chord in the output signal. If you use frequency scaling (in -> FFT -> scale -> IFFT -> out), the chord will still sound like a chord, regardless the scaling factor.

I'd certainly like to see the article from Australian electronics magazine, out of curiosity, if nothing else.

SioL

Well, at least it'll be audible, but maybe not as perfectly sounding as your solution.

I'll be checking the net for DSP code as this intrigues me quite a bit. Time to jump into the DSP thing.

Which brings me to another sub-topic, if you wanted to start playing with DSP, perhaps some simple filters, possibly using AVR for a start. I know its not the perfect part for the job (floating point calc). Where would you start looking (besides google)?

SioL

solution.

perfect

I'd use 16 bit fixed point to start with. It is enough for most filters. Depending on your milage on writing software, you might be better of buying a DSP evaluation kit. These come with working examples and a suitable AD/DA converter.

You can also use your PC to write DSP algorithms, dump the result to a file and use a program which can read raw data (like CoolEdit) to play / inspect the result. This is how I usually test DSP algorithms.

One of the basics you'll need is a piece of software with which you can calculate filter parameters. These can be found with Google. The links page on

Thanks, I've already saved that link from your previous post. I'll check it out.

SioL

An interesting different idea:

If you hear a buzzer running at 5 Hz theough a system that only outputs frequencies above 20Hz, you still get the impression of 5Hz. If it slowly sweeps up to 7Hz, you hear a smooth rise in frequency. You don't hear a sudden drop in frequency as the 3rd harmonic comes within the pass band.

If the amplitude and fundamental frequency of the sound of the whale are what matter and not the harmonics, you may be better off hugely distorting the input signal.

I'm thinking something like this:

"you may be better off hugely distorting the input signal"

Ken - you are on target! In the above sample you hear a more desirable true sound instead of Donald Duck on helium. I generate the trailing

Below is the original 10hz sine wave graphic with "distortion".

This piezo/cylinder enclosure approach is what I think the hydrophone principles are also.

Ok, Ok stop laughing, is it a bit to analog? I am not an engineer.

• * * Christopher

Temecula CA.USA

It sounds quite good. It is easy to hear the frequency modulation.

It works doesn't it, so what's to laugh at. You could have done the same thing with a DSP and a bunch of software or a whole mess of op-amps and stuff. You solved the problem and got on with the job.