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Notes on underwater sound

Not a good idea to connect a piezo directly to the output of an iPod. Apparently the impedance is too low and it fried the audio circuit and battery. I should have just dropped it (the iPod) in the water instead of the piezo.

I was able to get excellent underwater sound using  a piezo for a mic – it was a little over an inch diameter, broken out of the radio shack black plastic case – with some hot glue to cover the wire connections – probably not necessary.

See this article about working with Radio Shack piezo transducers

http://www.edrums.info/radio_shack_piezo.htm

The speaker was a Dayton Audio Weatherproof Extreme Exciter – from Amazon – http://amzn.com/B0031K2XBA

And I used a small power amp to feed it. http://amzn.com/B0049P6OT

Note: the exciter also sounds great when its duct taped to a cymbal.

 

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RTTY encoding and decoding in Max

notes

Today I was able to get an AFSK (audio frequency shift keying) system running in Max – sort of – It encodes text into ASCII bits and decodes the signal back into text – with a clock set at around 30ms (32 bits/second) – but there is no clock synchronization yet. Or stop bits, etc., The patch just uses the transmitter clock to sync the receiver (cheating)

Listen to an example of the word ‘hello’ at 32 bits/sec

local file is in max teaching examples/rtty-sim5.maxpat

Next step will be to get receiver sync happening – then make it conform to RTTY standard – probably a few days effort for this, but at least this is a proof of concept.

The synchronization may need to happen at the sample level (gen~) because it requires finding the beginning and end of bits – in order to set the clock pulses accurately.

 

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Nonoo radio DSP tutorials (RTTY)

By Norbert Varga

http://dp.nonoo.hu/projects/ham-dsp-tutorial/

From the IIR RTTY tutorial, a Paper on decoding RTTY in Linux:

http://www.ele.uva.es/~jesus/rtty/rtty-2.0/doc/rtty.pdf

Other resources on RTTY / FSK decoding

  1. RTTY decoder application and paper describing the method.
  2. RTTY diddles, about the protocol
  3. DPLL theory
  4. Bit banging, simple bit synchronization
  5. UART character recovery
  6. FSK signals and demodulation
  7. FSK demodulation theory
  8. Receiver sync theory
Getting started on RTTY

http://www.aa5au.com/gettingstarted/rtty_diddles_technical.htm

 

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Ever shifting media

This morning I think about singing. And Assyrian stone reliefs.

As we hang on to the crest of evolution, media grows less permanent. Last month’s Twitter mashups are broken. The 1980’s Atrari synthesizer project gathers dust in a closet. 20th century wax cylinders locked inside museums.

Things to do. Memorize a song. Teach one to a child. This year, carve something in stone. Bury it next to a stream.

 

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Laser audio

Today I built a laser pen solar panel audio transmitter thing – using these two sets of instructions – for the most part:

It works great, but I should have used a battery case instead of soldering the batteries together.

Built it into a Sparkfun box:

The next step is to experiment with filters – like an aquarium for example.