audio – madprof's blog

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)

Listen Online

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).

Advent 2018 – Daniel Part 2! Listen Online!

Doorbell, Door Opens

S: Belteshazzar! It’s good to see you again…
You missed the last 3 sessions… How have you been?
I hear from Shadrack that you’ve been sealed in your rooms?
What progress did you make on your action steps?

D: I’ve prayed. I’ve fasted. I’ve repented. I’ve wept.

S: That’s great, er, none of them were things we talked about
last time – but they all sound… useful?

D: Yes. I had a vision.

S: That’s good, right? You’re the one who interprets the King’s
dreams and visions so…

D: I don’t. The Lord does. And He tells me what they mean.

S: Yes, of course. So, what did the Lord say this time?

D: It’s complicated.

S: That’s surprisingly candid, coming from Him.

D: Stop it. So I read Jeremiah’s prophercy, it’s we’re almost
finished with the 70 years until the Temple and our people
are restored – and we’re nothing like ready. That’s why I’ve
been praying and fasting and repenting – How could we
possibly be ready to return?
And while I was praying, the Lord sent an Angel, who told
me many things…

S: Like, er what?

D: Our people will return, we’ll finish rebuilding, the sacrifices
will resume – and in then a while later, the Messiah
will come.

S: That’s amazing!

D: But He’ll die – appearing to have accomplished nothing.

S: But – but – all the other prophercies say all kinds of things
he’ll do!

D: I know. I said it was complicated… and the Angel said
“appearing to have accomplished nothing.” So maybe he’s
going to do things in secret? Or somehow won’t be noticed?

S: That doesn’t sound very Messiah-like.

D: I know.

S: This is fascinating, but I think we’re getting a bit distracted…
What would you like to take away from our conversation?

D: I’d like to get some clarity about sevens.

S: Sevens?

D: Yes… Apparently they’re quite important. And we’re going
to have an awful lot of them before the Messiah comes.

S: Er, right. So, what are the key points of understanding these
sevens?

D: I’m not really sure. An Angel told me about them. His name was
Gabriel. He was really nice – He told me that I’m precious to
The Lord. I have a feeling he’s involved in this all some how.
And then he started talking about all these sevens… 70 sevens,
then another 7 sevens, and then 62 more sevens after that.

S: Is there a cultural Angel to understanding this angle? Or cultural
angle to understanding the Angel, I mean.

D: Do Angels have a culture?

S: I don’t know! You’ve met more than I have!

D: True. hm. It’s a good question. A cultural angle..
Well – creation took 6 days,
plus the Sabbath – but 70 weeks is less than 2 years – it can’t
mean that… we used to have special celebrations every 7th
year – I think it’s seven years… so about 500 years,
in total, I guess?

S: So… what actions will you take to move forward?

D: 500 years is a really long time! I could do a lot of action
steps in 500 years.
I think I need to go pray some more.

S: That’s always a valuable thing to do…
What do you want to remember from today’s conversation?

D: I thought this was just all something to do with us returning
to the Jerusalem soon – but I think it’s something bigger.
The Lord isn’t just preparing us for the end to our exile –
There’s so much going to happen.

S: Hmm. So you said you wanted to get some clarity about this…
Out of 10, how clear is it now?

D: Maybe Seven?

Elizabeth

This was written by our friend Becky Breckels and me, and then read by my amazing wife.

Door opening and shutting

Elizabeth: Zechariah! You’re home! How was the Temple? Anything exciting happen?

Pause as is if Zechariah is speaking

Elizabeth: What’s that love? I can’t hear you!

Slightly shorter pause as Zechariah gestures wildly

Elizabeth: Well I can’t understand you if you’re just going to stand there gesturing! *deep sigh* Fine, we’ll play charades.

Your eye. A drink? A can. Tying something… a knot? Oh! “I Can not”, you cannot what? Talk?

…

Elizabeth: What do you mean you can’t talk? You’ve never had any problems talking before!

Zechariah starts gesturing wings.

Elizabeth: What are you trying to say? Wings…a bird?

Zechariah shakes his head

Elizabeth: No…? Not a bird…well what else has wings?

Zechariah starts gesturing a halo

Elizabeth: What’s that supposed to be?! A circle above your head!?

Sounds like a heart? A Triangle? Half a triangle? That’s still a triangle! Second half of triangle? Ngle? Sounds like ngle?

Zechariah starts gesturing both wings and a halo

Elizabeth: …AN ANGEL! You saw an angel! Blessed be! An angel! Well…what did he say?

Zechariah starts gesturing writing

Elizabeth: He told you to write something?

Zechariah shakes his head

Elizabeth: You know this would probably be easier if you had your writing things. Now, where did I put them…(fades out)

Sounds of pots and pans clattering

Elizabeth: Ah! Here they are! Now, what did the angel tell you?

Sounds of writing on a blackboard or tablet

Elizabeth: We’re going to have a son!?

This is all a joke, right?

More writing sounds

Elizabeth: His name will be John?! But that’s not a family name!

This must be a joke. I’m going to go make dinner.

OK! Fine, I’ll wait. You’d better make the punchline worth it.

Continued writing sounds

Elizabeth: (Writing sounds throughout) …No alcohol…filled with the Holy Spirit! Spirit and power of Elijah! You’re serious? This isn’t a joke? Turn many to the Lord…prepare the people for the coming of the Lord! …For the coming of the Lord! The Messiah!? He’s coming soon then?

Zechariah shrugs his shoulders

Elizabeth: What do you mean you don’t know! … You didn’t ask!? You had an angel of the Lord standing right in front of you! And you didn’t ask him when the Messiah is coming!?

Zechariah shakes his head

Elizabeth: Hang on, you haven’t told me what any of this as to do with you having no voice…What did you say to the Angel?

Oh come on, don’t be embarrassed.

What did you do?

You thought it was a joke too? Oh come on. An angel shows up, of course it’s not a joke. Who would think such a thing?

You told the angel he was crazy?

Well, serves you right if you can’t talk any more.

…

Er, how long are you going to be silent for?

…

Until the baby arrives?! I guess we’d better buy some more writing equipment. And you really need to start working on your mime skills.

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.

—–

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.

——–

So, what do you think?