Audio Advent Calendar

Fri, 21 Dec 2018 01:24:44 +0000

This year the Creative Writing Passion-Group on board were asked to make a series of brief reinterpretations of the Advent story for every day at lunch-time on board.

Here’s my two contributions:

Daniel (Part 1)

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Phone Rings You have reached the extension of Meshack, Permanent Secretary for the office of Internal Affairs, Babylon. I’m afraid I’m unable to take your call, but if you leave a message and contact information, one of my scheduling staff will return your call. BEEP

Daniel: Mishack, this is Belteshazzar, if you could contact me please that would be great. I’ve had a bit of an odd, er, experience I’d like to talk about with you. Shalom, Click

Daniel: Oh for goodness sake Mishael - answer your blasted phone! It’s me again, Daniel. Look, the dreams have been getting stranger. I swear I’ve not touched a drop of the King’s wine. So there were these beasts, coming out of the sea, all mixed up - a leopard with four wings, a lion, a bear, hideous. This wasn’t some stupid nightmare. Nightmares are way more mundane.

I can remember so vividly, like I was actually there - I’m not going to tell you every detail now… it all ended, somehow with me seeing into the thoneroom in heaven itself! And there, a “son of man”, like, how you described the fourth man in the furnace? The same! And he shows up in the throneroom, and was greeted royally, and then gets made ruler of the whole planet! An eternal kingdom, full of every kind of people, diverse and spectacular, immense and unlike anything we’ve ever seen, Mishael.

So I went and asked one of the court guards what on earth was going on - and he told me it’s all about the future, the beasts are kings who are coming, and eventually the Most High will judge the last kingdom, destroy it, and hand it all over to an eternal kingdom of His people.

Look - I honestly don’t know what it all means, brother. Or why on earth I had this dream. I thought these dreams from the Lord were supposed to be meaningful? How can I make SMART goals or an Action Plan from something like this?!

It’s terrifying, seeing the horrors of so far in the future - I know the Lord will send this Son of Man in the end - but it’s such a long way off - why tell me now? I wrote it all down - maybe you could come by to read through it. Perhaps someone else will find it encouraging. Call me. Click

Daniel (Part 2)

Featuring the Prophet Daniel (played by me) and his Life Coach (played by Dan Potter).

Documentation, and how balanced audio cables work.

Thu, 07 Feb 2013 08:39:00 +0000

I finally had a bit more time this morning to write a bit more in the A/V manual. There’s lots of bits and pieces of documentation on board, but no comprehensive single getting started manual. So I’m writing one, bring together bits and pieces from all over the place, sorting out what documentation there is, updating schematics, etc.

Anyway, here’s the rough version on the article I just wrote about how balanced sound cables work. It’s pretty much my standard explanation of Balanced Audio, and aimed at people coming to A/V from a non-techy musical background, rather than for Electronics Engineers.
You may find it interesting. Then again, you may not.

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Sound is basically vibrations in the air.

TODO: more details, pingpong ball analogy?

Inside an (SM57) Microphone head.
That is the bit of plastic and the coils!This translates really easily into an analogue electrical signal: you simply turn the air vibrations into voltage vibrations.A Dynamic microphone does this by having a small bit of paper (or plastic) which vibrates with the air around it, and pushes against a very small copper coil which, moving inside a magnetic coil itself, generates a very-very-very small amount of electrical current.

TODO: more pictures.

This gets dumped down a wire, which gets amplified by (you guessed it) an amplifier into a very big amount of electrical current, which then drives a big electromagnet inside a speaker, which pushes another copper coil around, which is attached to another big bit of paper (the speaker cone), which causes the air around the speaker to vibrate – with the same vibrations that the microphone vibrated with, just bigger.

Simple, isn’t it? (well. Kind of.)

Balanced Audio Cabling

The trouble with simply dumping an audio signal down a cable, and picking it up at the other end is that your signal line, and return (usually ground) will pick up noise (say from A/C mains electricity, fluorescent lights, dimmers, mobile phones, etc) along the way.

Here’s an original signal:

And here’s some noise:

And the result:

This is a Bad Thing™.

So some clever engineers, back in the deep recesses of time figured out the following:You could take a signal, and before sending down the wire where it could pick up noise, invert it:

If we add the signal to the inverse, you get a grand result of nothing (e.g. -3 + 3 = 0).

Now, if we throw these two signals down a pair of very similar cables twisted round and round each other like crazy, then they’ll both pick up noise pretty much the same as each other:

Note that 3 (the original) + 1 noise = 4,
while -3 (the inverse) + 1 noise = -2. NOT -4!

This is really cool, because if we add these two signals together, we don’t get 0 anymore, we get no original signal, but you do get the noise (doubled).

So we’ll use our amazing maths skills again, and divide this doubled noise in half. (2/2 = 1).