Hey Harvey, 2 questions...

[tubedude]

1) The easy one... in your opinion, what would be the next step up in clarity, detail, and overall sound quality from the mxl 603s for overheads? Think paired with a Great River.

2) How is it that a mic diapragm can pick up more than one frequency at a time? I dont understand how it can vibrate at more than one speed simultaneously. Strange. What is odd to me, is that you can, say, crash a cymbal and come off of the snare into a full kit roll, and pick up everything down to the last tom roll including the full decay of the cymbal at the same time. Just seems like the mic would have trouble doing that... I mean, picking up that cymbal decay AND the entire tom roll and individual drum decays at the same time. That is a LOT of frequencies happening there. Maybe its so easy and obvious that I can't see it. Maybe not. Whats your take?

Peace,
P

 

[charger]

And while you're at it, a loudspeaker does the same thing! And: analog tape can record it, and so can digital bits... How crazy is that? I always just think of these processes as "magic" since I don't have the brainpower to process them otherwise, and I don't want to go insane.

 

[JFogarty]

its like these one dimensional things (just the "height" of the airpressure) can reproduce any possible sound that humans can hear. Wait a second. All the ear drum is is the same thing as a diaphram. Woah....

 

[Harvey Gerst]

I'm not sure I can explain this without some pictures, but I'll give it a try. I'm gonna keep it simple and limit the discussion to one speaker, one mic, a few instruments, and one ear.

When you hear one held low note (from say a cello), the string vibrates back and forth; the bridge vibrates the front of the cello; the front of the cello vibrates the air; the air vibrates the mic diaphragm; the amplified signal from the mic vibrates the speaker; the speaker vibrates the air like the cello did; and finally, your ear hears the vibration from the speaker and your brain says, "Whoa, dude. That's the sound of a cello.").

If I understand your question correctly, what happens when you add the sound of a flute playing a different note; how does this stuff keep all these different notes seperate when they are going all at once? The answer is amazingly simple - it doesn't keep the notes separate. No more than when you play a six note chord on a guitar and the signal is only coming out of two wires.

If the flute is playing a little trill while the cello is playing a single note, the speaker moves in and out in time with the low note, but the flute trill is piggybacked on that cello signal.

But the mic, and the speaker don't know about notes and instruments - they respond to air pressure, period. They listen and play back the SUM of the different air pressures created by all the different notes. It just puts out a signal that's the sum of everything it hears - the speaker or the mic doesn't know how all those notes were totaled, it just puts out the total. Your ear reconstructs that total back into separate instruments.

 

[cavedog101]

Harvey, you havent mentioned anything about 'wolfing'....theres a soundpost in all stringed instruments(other than guitar,mandolin,and banjo) and this creates a 'counter' vibration in most......this requires an intensive 'micing' technique that most people dont ever encounter.....p.s. i REALLY like the over the shoulder acoustic guitar thing...(i've been doing it for years without support)....an sm-81 over the shoulder and a large diaphram out in front is "THE BOMB".......YOUARE a GAWD!

 

[tubedude]

Thanks for the reply... I still dont think I get it, I may never...
Any reply to question #1? The important one!...

Thanks,
P

 

[Rochey]

Okay, here goes. I don't know what you remember from physics from school...

but first, try this... http://www.howstuffworks.com/

look for microphones, or sound or something. Right then... as for an explanation, HArvey covered most of it. But I always like to hear the same thing said in a different way!

I'm sure you've looked at a bass drum being kicked. You see the skin moving in and out really quickly. Well, as the skin moves out, it creates a change in pressure in the air. It squashes it, and expands it. These changes in pressure move towards your ear.

Now. This is the physics bit. Please forgive me.
First, you must know what a sin wave is. I think everyone has seen one. Remember physics at school, where they had the test tone, and hooked it up to a little screen? Thats a sin wave.

Each sine wave has a FREQUENCY. or how many times it repeats per second. The more it repeats, the the higher the frequency, and the higher the pitch.

Okay... phew, still with me?

I'm sure you've used cool edit or some other audio program before, and when you look at the audio, it looks like a hash of mess. There's no organisation in it, and it looks nothing close to a sine wave. Thats because Sin waves can add up. All of these little bits of compressed and expanded air kinda add up in a long equation.

the clever bit is in your ear. Your ear is a little bit like a graphic equaliser (or a spectrum analyzer). There are tiny little fingers in there that split the incoming air pressure's n stuff back into it's separate frequencies. These little 'fingers' wiggle (resonate) when theyr specific frequency in played, and then send a message back to your brain saying "This frequency has just been hit!"

Your brain then looks at a map of the instruments you know, and says "Okay, if I have these frequencies bunched together, then it must be a Cello" -- At which point you think... "ahh... a cello!"

Your brain is also clever enough to get recognise lots and lots of different frequencies, and can map many many complicated instruments.

So, in conclusion, All a microphone does, it take the air pressure at the point in the room, and convert it to an electronic signal. That signal gets amplified and then put to a speaker. You then see a speaker moving in and out. Which re-creates the air pressures. Your ear gets the changes in air pressure, then converts them to various frquencies, passes it on to your brain, and your brain says "Cello!"


good luck


rochey

 

[tubedude]

Well, I'm very aware, for years, of the way sound works, and the "waves" if you will, and how this affects phase relationships and all that jazz... what I dont get is this: there is a high pitched frequency, say, a cymbal. The diapragm vibrates at that frequency. Then, at the same time, there is a low frequency that rings, say, a floor tom. It seems like it would only pick up one frequency or the other, not both, because its impossible to "vibrate" in more ways than one (at least it kinda seems that way). I understand that it DOES work, it just doesnt seem like it would, if that makes sense. And piggy backing seems weird, too. Just one of those things that never makes total sense until something clicks. It just hasnt clicked yet.

 

[Rochey]

imagine that you could measure pressure between 10 and -10 Rocheys. (a new unit of pressure!)

When at the top of a wave, the pressure is at 10 rocheys (at say 10watts musical power), at the bottom of the wave, it's at -10 Rochey's.

Okay, lets say at 1 sample in time, a cello is at 8 Rochey's, and the cymbal is at -3 Rocheys. by adding them together, you get 5 Rocheys.

Now, in the next point (think of it like sampling at 44kHz) the cymbal is at +3 (because it's frequency is higher, is goes from high to low quicker) and the Cello is at 7 Rocheys (on it's way down slowly), the total Rochey's will be +10.

This is why you get all that mess on the screen when you look at audio, because the TOTAL PRESSURE at one point is what gets recorded through a microphone.

does that help?

as for your microphone dilemma, I'm sorry, I have no idea.

Rochey

 

[Rochey]

just a quick point. How many posts have i got to make before I stop being a Newbie. sheesh... is there a right of passage i must do?? like swallowing a goldfish or something??



Rochey

 

[ola]

It's not the quantity of posts, it's the quality....

 

[Rochey]

I think my work in setting a new standard should be rewarded!!! I'm up there with Isaac Newton. He has his measure of weight, I have mine in pressure!

Of course, there is that Pascal guy as well, but he's dead already, i hardly think he'll put up a fight.


just think, years from now, people with refer to the Rochey in the same sentence as decibels. wow...


Rochey

 

[nessbass]

Hey Rochey, you just made it! Welcome Junior Member!

Tubedude: I'm not at home at the moment, so I won't be able to make some pictures, which would definitely help, I guess. Try doing the following: record a low-frequency sine wave (say 150 Hz) representing the tom you mentioned in your example. Then record a higher pitched sine, (8000 Hz?) representing the cymbal. If you look at them, you will see that they're quite nice curves. Now, mix them together and record the mix (this is what you hear, and how the air moves when you listen to the two sines mixed together). Now look at the waveform. THIS is piggybacking! It's hard to describe here. Just look at it. You will mainly see the 150 Hz sine, that has been transformed by the 8000 Hz wave (look for holes or 'dumps' in the waveform.)

Hope that cleared the fog a bit,

David.

 

[Rochey]

Woohooo -- junior member at last! Kick ass!!!

Here's a picture of what nessbass talked about.

As you can see, when the level of a wave is positive, then the speaker is pushing out. That means that the air in front of it is squashed (or compressed) and when the level is negative, the air is expanded, as it's sucked towards the speaker.

The example shown here is a little bit too perfect, as both signals are in phase, but, it'll do.

Now, when you mix signals, be it in the real world or electrically, then they add up. So that when both signals are positive, you get an even bigger output. if one is positive and one negative then you get a smaller output. If both are negative, then you get a bigger negative number.

So, a microphone doesn't measure frequencies, it just continuosly measures changing pressure levels.

any help? have i missed anything?

Rochey

 

[ola]

See Rochey, your posts finally meet the standards Or maybe it's all them links to John's studio manual, which usually is the best reply to posts there when Sir John himself is not around.

Anyway, your explanations are great and I would just like to add that although your example is simplified, due to the in phase waves, it's exactly how it works. So to get a mental image of "real sound" just add more waves of different frequencies and patterns to Rochey's example and you'll get the irregular spikey frequency (representing sound pressure) pattern we know as sound.

I'll shut up now because I don't think I'm helping. Please make me a newbie again.

/Ola

 

[Rochey]

i'm feeling pretty good about myself now.

as for the links to John's site. It's so good! He must have spent sleepless nights working on it. You'd pay $30 for a book with that information in, and $40 for a book with a CD-rom of the excel file!!!!! (bloody bookshops!!)


Where is John at the moment, is he still on Walkabout in the middle of australia?

Rochey

P.S I'd just like to add, that my posting count has shot up by about 20 in the last 2 days. It's amazing what a man will do to avoid work...

 

[ola]

It seems that John went walkabout again...

His site is really the best. I even paid for the full copy, a few weeks before it became free...darn.

 

[nessbass]

stupid question?

Hey ola, Rochey:

What are you talking about?

David.

 

[ola]

Sir John Sayer's recording manual: http://www.saecollege.de/reference_material/index.html

It's my bible

 

[Rochey]

One of the guys who contributes to this forum (well, more in studio building n stuff)

He is a Demi-God. He knows everything, and he wrote a really really really good website, with everything there is to know about building a good studio, all the way to micing positions etc.

It's really very good.

i'm sure i've posted the address here somewhere...


read it, and then come back and ask who john is...

Rochey

P.S -- Maybe i should alter my signature to show the address!!!!
haheheheh