To pull or to push ?

PaulBrewer · 21-07-2012 12:46PM #1

I've been thinking about the mechanics of drum recording a bit....

If you think about it, in an ideal world, one would think that for maximum impact (taking it one wants that) every track in a mix ought start with a positive movement i.e. every track at it's begining should make the the speaker should push ? Right ?

Well, if you think about it, a down stroke from a drum stick is sending a 'pull' to overheads in drums i.e. the stick and head are initially moving away from the mic, so it starts with a negative movement .

Therefore, one might argue, that the first thing to do is reverse the polarity (thereby creating a 'push'/+ movement) on overheads and match all your other drums to that to taste ...

What do you think ?

madtheory · 21-07-2012 06:53PM

If you look at a slow mo video of a drum skin vibrating when it is hit, even at the very first strike there are several up and down vibrations happening across it at the same time. The notion of absolute phase comes from assuming that sound is a sine wave, when it's actually several sine waves at once- aka harmonics.

I did have a video of a vibrating skin, but I can't find it. There are some videos of vibrating strings taken with strobe type systems, and you can observe the same behaviour- multiple simultaneous vibrations.

i57dwun4yb1pt8 · 21-07-2012 11:49PM

i thought this was normal, ive always tended to have the oheads out of phase to the kick

kick is a push
oh is a pull

depending on angle of mic , the toms and snare can go either way -
straight down on head is a pull, parallel to head is a push , and in between is a suck it and see.

bottom of snare is usually a push, but needs to be checked with top of snare.

ride and hat mics need to be same as the overhead phase choice .

PaulBrewer · 22-07-2012 04:42PM

madtheory wrote: »

If you look at a slow mo video of a drum skin vibrating when it is hit, even at the very first strike there are several up and down vibrations happening across it at the same time. The notion of absolute phase comes from assuming that sound is a sine wave, when it's actually several sine waves at once- aka harmonics.

I did have a video of a vibrating skin, but I can't find it. There are some videos of vibrating strings taken with strobe type systems, and you can observe the same behaviour- multiple simultaneous vibrations.

Mad - its clear in a Daw which way the initial movement starts.

madtheory · 22-07-2012 07:12PM

Actually it's not clear at all! What you're seeing there is the result of a measurement. The DAW image is all of the harmonics averaged into one as amplitude. It is a 2D representation of a 3D phenomena. It's purpose is to facilitate editing. It is not showing you what is actually happening. That can only be seen with slo mo or strobe lit video.

So there's really no need to be concerned by it, as long as you've taken care to position the mics so that they measure the most pleasing/ appropriate bit of the harmonic soup! IMO the notion that one can create a drum sound in the mix is deeply flawed. One can only tweak what was recorded.

krd · 22-07-2012 10:07PM

madtheory wrote: »

Actually it's not clear at all! What you're seeing there is the result of a measurement. The DAW image is all of the harmonics averaged into one as amplitude. It is a 2D representation of a 3D phenomena.

Yes...And no....but more no than yes.

The sine wave in the DAW, is a clear representation of the voltage that will go to the speaker. That is the voltage that will push and pull the cone.

The sine wave is a 2D representation - but what it represents is the change in voltage to the speaker cone over time. And that voltage at any instant (remove time) is one dimensional. BUT ...When the cone moves, it pushes the air in 3D space.

Paul's idea is kind of right and kind of wrong. The first half of the wave cycle can be positive - it can push the speaker cone out. But the second half pulls it back. And this happens very fast. For a 60hz tone - the out push lasts 1/120th of a second.

That thing of seeing the cone seem to push out and stay out, is an optical illusion. It's actually going back forth really quickly. Even without a strobe light - your eyes will see strobe like illusions,

If a drum is being captured on two mics, If the recordings are in opposite phases, when they're summed you have a problem.

madtheory · 22-07-2012 10:50PM

Yes. That is why you make it sound the way you want when you're still in the 3D domain- i.e. mic positioning.

krd · 22-07-2012 11:30PM

Not absolutely relevent....but I just thought interesting.

The pick up in Damon Albarn's guitar is a speaker cone (yes I know there's also a second pick)

https://www.youtube.com/watch?v=lGzQgTK7ocM

PaulBrewer · 23-07-2012 09:44AM

madtheory wrote: »

Actually it's not clear at all! What you're seeing there is the result of a measurement. The DAW image is all of the harmonics averaged into one as amplitude. It is a 2D representation of a 3D phenomena. It's purpose is to facilitate editing. It is not showing you what is actually happening. That can only be seen with slo mo or strobe lit video.

So there's really no need to be concerned by it, as long as you've taken care to position the mics so that they measure the most pleasing/ appropriate bit of the harmonic soup! IMO the notion that one can create a drum sound in the mix is deeply flawed. One can only tweak what was recorded.

Fair point Mad - but you surely can't argue that there has to be an initial FIRST movement and that should be a 'push' ?

krd · 23-07-2012 11:32AM

PaulBrewer wrote: »

Fair point Mad - but you surely can't argue that there has to be an initial FIRST movement and that should be a 'push' ?

No. For a sound wave, in the air, there has to be a push and a pull......and pull first then a push, will get the same sound wave (to your ears it will sound the same, but the polarity is reversed) . On a speaker, if you switch the polarity of the wires, you won't notice a difference. (Or course with two stereo speakers if one has the wrong polarity you'll get strange phasing effects)

I think the idea of having a different polarity on the over heads, to the kick, is when they are summed, there is a phase cancellation that reduces the bleed, and gives clarity to each.

The positive and negative, in terms of the polarity of the speaker cone are relative to the cones position at zero volts - when no power is passing through it.

There is a coil of copper wire in the speaker and a magnet. When no current is flowing the coil doesn't move. When the current flows in one direction, the magnet wants to push the coil away, and when the current flows in the opposite direction, the magnet pulls the coil towards it.

When you're looking at the sine wave in your DAW, the wave is literally saying Push, Pull, Push, Pull, Push, Pull.

If you're looking for something that sounds like a push, that's something else. A kind of perceptual thing.

studiorat · 23-07-2012 01:47PM

I'm with Madser and Krd on this. Whether it's a push or a pull is immaterial, both are perceived as a change in pressure and thus as sound.

One question is, when a the snare drum is hit. Does the microphone diaphragm react to the drop in pressure from the head moving away? Or does it react to the sound pressure front from the sound the drum skin creates?

And here's a vaguely related video !

https://www.youtube.com/watch?v=Qf0t4qIVWF4

PaulBrewer · 23-07-2012 05:19PM

If it doesn't matter which way its going (and therefore the signal the mic is recreating) - then the polarity of the mic wouldn't matter would it ? Huh ?

I'd say it's unlikely the overhead mics react to the pressure drop as the air in-between could easily absorb that - and probably wouldn't be fast enough to react .
However that's speculation on my part.

PaulBrewer · 23-07-2012 05:37PM

krd wrote: »

Not absolutely relevent....but I just thought interesting.

The pick up in Damon Albarn's guitar is a speaker cone (yes I know there's also a second pick)

https://www.youtube.com/watch?v=lGzQgTK7ocM

Don't mind all that ! There's a lad with a 8 string cello !!

krd · 23-07-2012 09:13PM

PaulBrewer wrote: »

Don't mind all that ! There's a lad with a 8 string cello !!

I think they're period instruments. Baroque. 17th century.

And as mixes go. They did a much better version for the Guardian. Where the girls voices were brought more to the front. On Later, they're kind of getting Eric Clapton's backing singers mix.

i57dwun4yb1pt8 · 23-07-2012 11:02PM

if you reverse the leads on a speaker you WILL notice a difference

which is the point all along .

reverse cabled speakers have less low end and sound choked.

at least any i have heard this done to have had this happen.

TelePaul · 23-07-2012 11:45PM

That looks like a feedback controlling device to me. Could be wrong of course, but it'd be an odd place to position a mic.

madtheory · 24-07-2012 09:40AM

DaDumTish wrote: »

if you reverse the leads on a speaker you WILL notice a difference

which is the point all along .

reverse cabled speakers have less low end and sound choked.

at least any i have heard this done to have had this happen.

You mean when both speakers are in phase, but the polarity is wrong? I could imagine this happening with a really good, really powerful system because most audio signals are asymmetrical- they have more positive energy than negative. So that could make it quieter. However, I can't honestly say that I ever noticed. Two speakers out of phase makes me nauseous though.

PaulBrewer · 24-07-2012 10:32AM

One of the (many) reasons I dislike department stores is the random way speakers are out of phase !

madtheory · 24-07-2012 01:17PM

On the other hand, swinging on of those cigarette pack guitar amps around on the end of a guitar lead makes an excellent Leslie speaker.

jtsuited · 24-07-2012 05:10PM

PaulBrewer wrote: »

One of the (many) reasons I dislike department stores is the random way speakers are out of phase !

haha my personal favourite is when they play certain songs (the other day it was a song off Pet Sounds) and you hear the drums coming from 60 feet away and all you hear from the nearest speaker is the vocals and some other bits.

madtheory · 24-07-2012 05:31PM

Ya that's great crack! Especially Beatles.

Wondering about the Pet Sounds old fashioned stereo thing you're describing- AFAIK the only stereo mix is the Mark Linett one from 1997, and that does not have the extreme panning you describe? I'd like to hear a mix like that! It's a great way to hear how they did stuff.

I've been listening to Revolver and Pepper in mono and those are generally better mixes- no Beatle was ever present for a stereo mix in the sixties except for Abbey Road.

jtsuited · 24-07-2012 05:43PM

madtheory wrote: »

Ya that's great crack! Especially Beatles.

Wondering about the Pet Sounds old fashioned stereo thing you're describing- AFAIK the only stereo mix is the Mark Linett one from 1997, and that does not have the extreme panning you describe? I'd like to hear a mix like that! It's a great way to hear how they did stuff.

I've been listening to Revolver and Pepper in mono and those are generally better mixes- no Beatle was ever present for a stereo mix in the sixties except for Abbey Road.

just thinking about it now.....yup it was definitely a song off Pet Sounds. the one that goes 'blah blah blah blah, how independent I'd grown, but that's not me'

kunst nugget · 24-07-2012 05:53PM

jtsuited wrote: »

just thinking about it now.....yup it was definitely a song off Pet Sounds. the one that goes 'blah blah blah blah, how independent I'd grown, but that's not me'

The Blah, Blah, Blah Song? One of Brian's best…

madtheory · 24-07-2012 06:05PM

That would be You still Believe in Me. No extreme panning on the Mark Linnet mix. Stuff is panned to one side, but there's a nice wash of reverb to spread it. Maybe they'd accidentally connected the phase difference instead of stereo, so anything that's panned centrally gets cancelled. I've definitely heard that problem before with piped music. That and extreme settings of "stereo enhancers".

jtsuited · 24-07-2012 06:55PM

madtheory wrote: »

That would be You still Believe in Me. No extreme panning on the Mark Linnet mix. Stuff is panned to one side, but there's a nice wash of reverb to spread it. Maybe they'd accidentally connected the phase difference instead of stereo, so anything that's panned centrally gets cancelled. I've definitely heard that problem before with piped music. That and extreme settings of "stereo enhancers".

ah that must have been it.

PaulBrewer · 11-08-2012 05:32PM

http://mhsecure.com/metric_halo/products/software/channelstrip.html#tab=3

Some interesting reading on mic delaying .

To pull or to push ?

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