logos hope – madprof's blog

I use WordPress at work, it’s the engine behind fr.om.org, transform.om.org and most of the other sites that we run for clients.

I’m in two minds as to whether I like it or not. Some things are great. For users (content authors, the people writing blog posts or static pages), it’s fine. Easy to understand and use. For writing plugins and templates, it’s… Well, kind of messy and ugly, but doable. For instance, rather than have 1 HTML template “base” file, with a block saying, “put posts here, and wrap each one in x,y,z”, you have a header.php which has only the start of all the HTML, and a footer.php which closes it all, and a content.php, a content-post.php, and so on, and you have to keep them all synced up. Also, since it’s designed for running on old PHP, it doesn’t use namespaces or other ways of keeping code clean, so all functions in all plugins and all templates are all global scope, so to avoid bumping in to each other, you have to name all your functions stuff like, “madprofs_teapot_plugin_get_resource() and similar. Then at the same time, WordPress has multiple global functions of its own, some called things like, the_post(), others like wp_get_cached(), (so prefixed with wp_), and others in other styles. Messy.

Still, it gets the job done.

So when I wanted to update and clean up the brummie@sea blog, I thought I’d just stick with blogger. It works, it’s what I already had. But then, accidentally, while trying to update it, I lost the entire design, and putting it back together was this awful mess of Google-XML/HTML confusion, I thought, “you know, stuff it, I’ll just use WordPress.” So I span up a site on the server (in about 2 minutes), pointed the blogger importer at brummieatsea.blogspot.com, let it chug away for a few minutes, and here we are.

I’m just using a very simple built in design for now, (with my own background), but it seems to work. I now don’t have to worry about Google turning off blogger like they did with Reader and GoogleCode, and since I use WordPress at work, I understand what’s going on pretty well.

That all said, we’re now on the ship, trying to settle in. We have a really nice cabin. Jet lag wasn’t fun, especially with the baby, but we’ll get through it. Yesterday Becky drank a big milky drink by accident – we thought it wasn’t cows milk but plant based, and last night and tonight David has been awful – screaming for ages and refusing to be comforted or to sleep lying down in his bed. So that does seem to confirm that maybe it is a lactose intolerance at the moment – hopefully he’s back to normal in a day or so.

Work so far is just cleaning the various venues. We’ve not even begun to start installing new equipment or doing anything really technical. We’ve got the lights out of their bags and air-blasted them all, cleaned many surfaces and TVs and vacuumed and dusted. It’s going alright. Still sooo much to do.

For Becky and David things are a bit odd still, it’s quite odd not having a fixed job to do, not knowing what to do most of the day, not having cornerstone to visit, not really knowing many people yet, and so on.

Anyway, we’re here, the flights weren’t bad at all. We couldn’t check in online due to some weird computer bug, but at the terminal while we were checking in we asked about getting a bassinet for David to sleep in, and they said they could get us one, but the lady recommended us instead to not get one, as he is quite big, and had a seat booked, and instead found us a row of four seats with no one else on the row, so we could make a bed for David there, which gave us all a lot more room. So on the second flight, both mother and baby could actually lie down and get some proper sleep, and arrive not looking like zombies.

I now have this weird mental image, after that last sentence, of a zombie “madonna and child” (very un-)orthodox icon…

That aside, we’re here!

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).

And we can subtract this 1 noise from the noisy original signal (4-1=3)

Voila! The original clean signal is back again.

This is (roughly speaking) how balanced audio works. And since almost all professional audio equipment runs with balanced circuitry, all we need to do is make sure the cables are in good shape, and then everything works magically with hardly any noise.

This is why for balanced cables (XLR/Mic, or TRS jack) you have 3 pins: +, -, and ground. The ground is connected to a wire-mesh sheath around the other two, to try and keep as much noise away as possible.

(Technically, you don’t need to invert the signal, you could just use an empty zero, but for various impedance, op-amp, techy reasons, it works better if you do.)

Sometimes the ground wire will pick up noise itself, or due to being connected to different grounds at both ends of the circuit (say a piano on stage, and the A/V room sound desk) it will end up with a bit of random leaked current running down itself. This can show up as noise, so you often use a Ground-Lift switch to disconnect the ground at one end or the other, which can sometimes help.

A DI box takes an unbalanced signal, and turns it into a balanced one, which means you can send a signal a long way without noise.

Remember how the two wires have to be twisted together like crazy? This is so that if there is some noisy thing (like a flurescent light) nearby, both wires will be equally effected. This is so important, that for broadcast audio, sometimes cables with 4 or more wires are used. The + signal on 1 & 3, the – signal on 2 and 4, and then all of these are twisted together. There are brand names of these cables such as QuadStar, etc. Usually this is somewhat overkill for regular live sound though, as the cabling is much stiffer and harder to use day to day.

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So, what do you think?