Free college course: Intro to Digital Sound Design

[Caroluna]

For Fearfaoin:
Q -What music is played at a mathematician's funeral?
A -A -The Fourier Requiem

Sort of like this, but different.
http://www.youtube.com/watch?v=NaIq8M47TvY


For Nano:
Q- What's blonde and half naked and plays the Ryuteki?
A -Lady Gagaku

[Nanohedron]

Oh, lord.

[Caroluna]

teleological listening

I want to watch those vids again. He was quoting writers who were using words in a very specialized, technical sense. (I think the general topic would be "philosophy of music?) When he said "teleological listening" I think he meant -- listening to music as if it contained sentences with a beginning, middle and end. The listener experiences the moments of sound expecting them to go somewhere. If you are brought up in a western musical tradition it's very disorienting(hee hee) when the music doesn't go anywhere.

but I do think it's not amiss to say that one needs very "long" ears to listen to (and comprehend!) Gagaku without squirming.

I definitely enjoyed the "sanitized" version much more. Fearfaoin, do you remember how that modern composer made that version? Did he actually "weed out" some of the nasty harmonics with sound software? Or did he just use more "civilized" instruments?

The cleaned-up version seemed meditative to me. The "authentic" version reminded me of the howling of cats in heat. Evocative in its own way, but...

Those 3 lectures had some bizarre ways of phrasing things. I think I see where he was getting at but I'd like to try again. "Acoustic Ecology" "the ecological approach to music perception" "Keynote sounds" "Soundmark" "Soundscape"

The following is copied from one of the powerpoint slides --

Acoustic Ecology is the study of sound (including music, speech, noise and silence) as a component of natural and artificial environments, with effects on health, cognition and culture. [It is] an integrated field of study with links to anthropology (cultural attitudes towards sound, silence, music and noise) and environmental sciences (the effects of acoustical environments on health and culture). The ecological approach to music composition suggests a different approach to composing music that may be termed 'composing through sound'. In this approach, processing techniques are used to reveal the inner levels of meaning and symbolism contained within the timbres of familiar sounds. Using these methodologies, we may be able to (re)create models of a more balanced relationship between ourselves and the environment. -- Barry Truax

Y'know, I think one reason this might be interesting to me is - I would like to compose music loosely based on the sounds of my aviary birds -- slowed down, lowering the pitch, "fixing" their intonation.

[fearfaoin]

I definitely enjoyed the "sanitized" version much more. Fearfaoin, do you remember how that modern composer made that version? Did he actually "weed out" some of the nasty harmonics with sound software? Or did he just use more "civilized" instruments?

When I first listened to that lecture, I assumed he used software.
But I found that spot again, (15 minutes into "Music & the Environment Part Two"). Hideki Togi is the adapter in question.
Prof. says, "Playing here again for a Gagaku ensemble" so it sounds like he performs the piece in a less "rough" style (not sure if he actually changed the instrumentation).

[Caroluna]

And now -- on to Week 2!

I watched the 2 lectures on microphones last night. This is something I know virtually nothing about -- so for me it was at just the right level of detail. I hope you audiophiles out there weren't bored!

Could someone post a picture of the inside of a dynamic mic? I found some diagrams but no photos. I'm having trouble visualizing how the coil attaches to the diaphragm.

While I was looking, I found this:

Blimps (also known as Zeppelins) are large, hollow windscreens used to surround microphones for outdoor location audio, such as nature recording, electronic news gathering, and for film and video shoots. They can cut wind noise by as much as 25 dB, especially low-frequency noise. The blimp is essentially a hollow cage or basket with acoustically transparent material stretched over the outer frame. The blimp works by creating a volume of still air around the microphone. The microphone is often further isolated from the blimp by an elastic suspension inside the basket. This reduces wind vibrations and handling noise transmitted from the cage. To extend the range of wind speed conditions in which the blimp remains effective, many have the option of a secondary cover over the outer shell. This is usually an acoustically transparent, synthetic fur material with long, soft hairs. Common and slang names for this include "dead cat" or "windmuff". The hairs deaden the noise caused by the shock of wind hitting the blimp. A synthetic fur cover can reduce wind noise by an additional 10 dB.

"Dead cat" and a "dead kitten" windscreens. The dead kitten covers a stereo microphone for a DSLR camera. The difference in name is due to the size of the fur.

The things you learn on Wiki!

[fearfaoin]

I watched the 2 lectures on microphones last night. This is something I know virtually nothing about -- so for me it was at just the right level of detail. I hope you audiophiles out there weren't bored!

unfortunately. The MIDI lectures have some interesting info, though.
Though I do think I know now the reason our sound engineer came into the studio 2 hours before we started to "warm up" the condenser mic we used for the guitar on Piper's Refrain. It needed to get the charge evenly distributed across both plates, and you don't want to do that too fast lest you hurt the diaphragms.

Could someone post a picture of the inside of a dynamic mic? I found some diagrams but no photos. I'm having trouble visualizing how the coil attaches to the diaphragm.

There's not much to see, I'm afraid. The diagrams will serve you better.
The diaphragm is usually built into a capsule with a backplate and the coil of wire, and it is often impossible to take apart without destroying something.

The diagram above refers to this diaphragm design (used often in recording mics):

Which can be seen in place as the copper-colored circle in this picture:



Whereas the design in this diagram (more common in vocal mics and probably mass produced more cheaply):

... refers to the capsule at the end of the red and white wires in this picture:

[Caroluna]

unfortunately.

It was fun to see the different patterns of cardioids. My husband is a mathematician, and one of his hobbies is making art which uses cardioid patterns. I didn't know they had a connection with microphones!

The idea that some microphones are sensitive to a wider range of frequencies -- Is that why old-fashioned cassette tape recorders make your voice sound like a chipmunk? (Maybe you are too young to have experienced that) The microphone wasn't picking up the lower frequencies and so it changed the timbre of the voice? The "secret sauce" of frequency blends wasn't there anymore.

I'm still having trouble understanding the dynamic mic.
Sound waves move thin membrane of PVC.
Thin PVC membrane is ?attached to? thin copper wire
Copper wire is wrapped around a core
Core is surrounded by a permanent magnet
OK, we know how they work
http://knowyourmeme.com/memes/fcking-ma ... -they-work.

but when you look at the wire/core thing and the outer permanent magnet, which one is physically moving? And if this set-up is so sensitive that sound waves can make it move around, then why did the prof. say that rock musicians can be really rough with these microphones?

[fearfaoin]

The idea that some microphones are sensitive to a wider range of frequencies -- Is that why old-fashioned cassette tape recorders make your voice sound like a chipmunk? (Maybe you are too young to have experienced that) The microphone wasn't picking up the lower frequencies and so it changed the timbre of the voice? The "secret sauce" of frequency blends wasn't there anymore.

Yeah, I know what you're talking about. It could either be the microphone, the tape recording head, or the preamp, but in any case you're right, it wasn't capturing the full dynamic spectrum of the voice (or was limited in which parts of the dynamic range got more power).
You can get some of the effect by doing a voice recording in Audacity and applying a High-Pass Filter (under the Effect menu).
When the phone system was developed, the designers limited the frequency range to about 4000Hz, which was enough for the human voice. But if you try to play music over the phone to another party, it will sound pretty cruddy because the frequencies > 4000Hz will be filtered out by the phone system.

I'm still having trouble understanding the dynamic mic.
Sound waves move thin membrane of PVC.
Thin PVC membrane is ?attached to? thin copper wire
Copper wire is wrapped around a core
Core is surrounded by a permanent magnet

but when you look at the wire/core thing and the outer permanent magnet, which one is physically moving? And if this set-up is so sensitive that sound waves can make it move around, then why did the prof. say that rock musicians can be really rough with these microphones?

I tried to find a good animation for dynamic mics, but the best I could do was for speakers (which is a very similar setup):
http://electronics.howstuffworks.com/speaker6.htm
In a speaker, when you put a current through the coil of wire, it generates a magnetic field in the iron core (the same law of physics that gives us electromagnets and solenoids). The direction of the field depends on the direction of the current: touch the ends of the coiled wire to the terminals of a 9-volt battery, you might get a north-south field, swap which wire is touching which battery terminal and you get a south-north field.

The core and coil are surrounded by a permanent magnet (which is called permanent specifically because its field direction never changes). When you have a current that is causing a north-south field in the coil, the magnet will push the core one way, when the current is causing a south-north field, the magnet pulls the core the other way. This is how the core can move in a way that follows the current.

Attach the core to a cone made of some flexible material (paper, plastic, etc), and you make that cone move in the same way the core does, which makes the air move the same way, which makes sound.

Now, the reverse of the physical law that makes speakers work also is true: instead of applying current to the coil so the magnet makes the core move, you can physically move the core and the magnetic field from the magnet will generate an electrical current in the coil.

So, if you attached a voltmeter to the wires of a speaker and took your hand and tapped the middle of the speaker cone, you would see a tiny change in voltage on the voltmeter (and it would go from positive to negative as the direction of the cone's movement changed).

But don't actually do that because it will break your speaker's cone. They're delicate. Instead, we developed microphone diaphragms that are not as delicate and that don't have to move their core nearly so much to generate a current.

In a dynamic mic, there is a diaphragm which moves with the sound waves in air. The diaphragm moves a core which is attached to the coil of wire. So the permanent magnet holds still, the diaphragm/core/coil move as a unit inside the magnet and this causes a current in the coil. That current is really, really small, so dynamic mics have to have some preamplification.

You're intuition about the loud singer is right, though. The short answer is that materials scientists are very clever. The long answer is that there are different dynamic mics for different applications. A vocal mic will have a stronger diaphragm to handle strong pulses (and the occasional drop onto the stage), but this is often at the expense of the its ability pick up extremely soft sounds very well. There might also be more room to move before the diaphragm physically hits something else (which would be damaging). A vocalist, even while screaming, is never going to be as loud as a bass drum or a tuba.
A recording mic may be able to better able to pick up subtle sounds but might be more easily damaged by very loud impulses.

Still, a condenser mic will always be more fragile than a dynamic because it has two plates so close together that they would gladly run into each other (ouch) at the slightest provocation.

[MTGuru]

I guess the fact that a dynamic microphone and dynamic speaker are essentially the same device "in reverse" is the take-away, if that's not obvious. Old style intercoms were a good example. A single speaker, and to talk you press the transmit button and yell into the speaker.

why did the prof. say that rock musicians can be really rough with these microphones?

Well, that doesn't mean while the mic is connected to your PA. If you hammer nails with your SM57 while it's plugged in, you're going to generate some real heavy metal noise. It's just that the geometry and construction of a passive coil and magnet are more rugged against being permanently unaligned by shock damage.

[fearfaoin]

I guess the fact that a dynamic microphone and dynamic speaker are essentially the same device "in reverse" is the take-away, if that's not obvious. Old style intercoms were a good example. A single speaker, and to talk you press the transmit button and yell into the speaker.

That's fun. I didn't know about those.

[Caroluna]

Thanks Farf for the explanation, and especially that animated diagram. Perfect! Now I can picture it.

I just learned that there's a thing in a speaker called a "spider"!! Don't tell Izz.

BTW -- Did you notice that the back of the mixer had a switch were you could turn the phantom power on and off?
I kept picturing this.



"Nice take, guys. But who's your friend in the purple leotard?"

[fearfaoin]

Thanks Farf for the explanation, and especially that animated diagram. Perfect! Now I can picture it.

Whew. I'm glad. I wasn't sure if I had any words left.
Oh, wait, here's one: Falafel.

I just learned that there's a thing in a speaker called a "spider"!! Don't tell Izz.

I was not aware of that nomenclature, either. YLSNED (You Learn Something New Every Day: It's the new "YOLO". Tell your kids!)

BTW -- Did you notice that the back of the mixer had a switch were you could turn the phantom power on and off?
I kept picturing this.

Oh my. Every time we encounter a new sound guy he has to ask us if any of our mics or D/I boxes require phantom power. Now, in those times, the Ghost Who Walks will jump in my head.

[TC]

Some useful info in Week two. The most important thing I learned was that you can watch the video at X 1.25 speed without much audio degradation. Only did this on the Microphone section which was again, very familiar turf.

The MIDI section was informative. However, it seemed like a survey of the history of MIDI. Sadly, I was around during this history. Nothing really useful for me now.

The Audacity section, on the other hand, filled in a lot of gaps for me. I have used the program minimally but only for recording and playback. I haven't done much mixing or processing. Seeing someone else perform and explain some of these functions on the screen was really useful. Anxious to find some time to explore this more fully.

Went on and did the mid-term exam, getting 53 out of 60 correct.
Not great, but in my defense, there were 2 questions which I completely disagree with the answers. See if you can guess which ones when you get there.

[Caroluna]

However, it seemed like a survey of the history of MIDI. Sadly, I was around during this history.

Alas, me too

The Audacity section, on the other hand, filled in a lot of gaps for me.

The part I've liked the best so far was the one on mixers. I've worked with mixers before but only knew the function of about 10% of the knobs.

Went on and did the mid-term exam

Do you know when is the deadline on Sunday? I'm catching up today -- my dad was in the hospital all week. He's getting out of intensive care now, and suddenly my brain is functioning again. Funny how that works...

[TC]

I did notice that the mid-term deadline was 12 am Monday. So you've got all day Sunday!