reversing phase on microphones

[smalljoshua]

Wouldn't a lead also be cheaper?

 

Josh

[Seano]

Isn't snare sound just snare sound regardless of whether it's live sound or recorded? Sorry if I'm missing something obvious here.

 

You are missing something, but its not *that* obvious.

The OP is talking about using two mics on the snare drum, one is above the drum, the other below.

Probably oversimplifying here, but as the drum skin is struck it moves away from the top mic and towards the bottom - the sound entering one mic is in effect polarity reversed compared to the other. If you then mix the sound from the two mics together, there's a good chance of getting some odd phase-cancellation type effects - hence the need to 'phase reverse' one of the mics first.

[bruce]

The desk outputs might not last too long though . I'd have thought a trailing box or a lead would be a safer bet.

Yeah, you wouldn't want to plug them directly into the desks. (and it'd be inputs, not outputs :wacko: )

but that's what short XLR patch cables are for...

 

 

 

Wouldn't a lead also be cheaper?

Perhaps, but it's only a difference of pennies. Remember, you're only talking about using one or maybe two of these, not dozens.

 

Personally, I hate having any non-standard cables - I'd much rather have all cables standard, and a box of barrel adaptors.

[Bobbsy]

I tend to make anything non-standard out of some bright yellow cable I picked up a few years back. (It used to be red but, under certain lighting, red can look like black if you see what I mean.) If the sort of "non standard" isn't immediately obvious, I'll also use a label. I have a tub or two of barrel adaptors but find they can get messy since I make myself use a short trailing lead to avoid strain on mixer ins/outs.

 

Bob

[Albatross]

You are missing something, but its not *that* obvious.

The OP is talking about using two mics on the snare drum, one is above the drum, the other below.

Probably oversimplifying here, but as the drum skin is struck it moves away from the top mic and towards the bottom - the sound entering one mic is in effect polarity reversed compared to the other. If you then mix the sound from the two mics together, there's a good chance of getting some odd phase-cancellation type effects - hence the need to 'phase reverse' one of the mics first.

 

This is slightly OT from the OP's question and may need to go to a new thread.

I have thought a lot about this over the years and am interested in others thoughts about this.

 

There's no disagreement that 2 mic's on the same instrument will give phase cancellations due to different distances from the sound source.

 

What is a source of dispute, with micing top & bottom of a snare, is are the 2 mics picking up the same sound in the first place?

Does the top mic pick up the sound of the top drum head, with the bottom mic picking up the sound of the bottom head & the snares themselves? If this is the case then there are 2 distinct coincident sounds that are mixed together.

 

Or do BOTH mics pick up the overall drum sound, in which case polarity is not really an issue, but Phase/distance from the sound source is.

If the drum as a whole is making the sound then any mic pointed at it will be at the same 'edge' of a sound wave as the sound will radiate out from the drum on a spherical (ish) pattern. This negates the concept of one mic being 'out of polarity' with the other, or that just because the skin of the drum is bending one way that the polarity of a sound wave will be inverted into another microphone.

 

In a standard dual micing situation, both mixed sounds (1. combined Mics & 2.with one mic polarity inverted) will have phase cancellations of some sort, the 2 options are usually to give 2 different combinations changing the overall tone of the 'mic'ed' sound.

 

or another way of thinking about this is... if you miced a guitar from the front and from the back would you polarity invert one of them, and why?

[berry120]

Like Bob, all of my non standard cables go with a seperate colour (it is in fact red at the moment, though I see what you mean about it being a bit tricky to make out in some lights!) They then have a label to say what kind of special cable they are (ground lift, phase reverse etc.) I prefer them to barrel adaptors simply because I've got no worry about plugging them straight into the desk!

 

In terms of if you mic-ed a guitar from the front and back, I wouldn't invert one, because the sound at the back is probably (though I may be wrong here, I've never tried it!) the sound that's come out of the soundhole and has travelled behind the guitar. Whereas on a drum, it'll be the sound that's directly generated behind the skin rather than the sound that comes from on top and then travels underneath. Again that's probably an oversimplification and I'm sure someone can explain it better than that!

[paulears]

I've always assumed the requirement for inverting one is because if you remove the drum, the two mics are facing each other - so a positive pressure one way gets cancelled - reversing one allows them to mix, getting the two tonal differences between top and bottom and allowing a mix.

[Bobbsy]

I tend to put the reversed polarity on snare in the "try it and sometimes it helps, sometimes it doesn't" category.

 

Bob

[berry120]

Perhaps I'm drifting a tad off topic, but does anyone reverse the polarity of the kick drum because it's on the other side of the beater? I tend to out of habit thinking about it, though I suppose it might not always be the best way..

[frosty55]

I would assume the desk does not have this feature, hence the question.

 

If you could tell us Frosty55 if it is for live sound or recording?

 

John Denim.

 

The desk is a Studiomaster Trilogy 166. We will be recording a demo very shortly with the snare mics.

[Mark Payne]

I hope to give you a definitive answer to this and a simple bottom line!

 

You cannot think about the positive vs negative pressure idea as the top and bottom skins of a snare beat at different frequencies and are asyncronous in time. The two snare mics are effectively listening to different instruments. At lowmid frequency (say 200hz) one might assume that the snare depth is acoustically small cf the wavelength so the mics are effectively in the same place and so the orientation is now interesting and the phase reverse may have some defineable/predictable effect.

 

At himid freq (say 4k) the mic separation distance creates way more interesting phase mix issues than the mic orientation and a question about phase reversing for it is the wrong question.

 

And now the bottom line:

The drum will sound different and will eq itself due to complex interactions beteen the two mics depending on relative position and relative phase (or polarity). You chose the one you like the sound of!!!..... Remember the ghost notes live in the bottom head (IMO).

[Matt Pengelly]

I tend to put the reversed polarity on snare in the "try it and sometimes it helps, sometimes it doesn't" category.

 

Bob

 

My sentiments exactly. At the risk of massively over-simplifying, polarity inversion on a desk channel has something of the voodoo about it.

 

Like Bobbsy says, try it and if it sounds right then it is!

[Bobbsy]

To frosty55: if you're multi track recording with each mic on a separate track then I wouldn't worry about the polarity at the record stage. Just position the mics for the best sound--with any decent mixing software, you can experiment with the polarity later in the mix process (and if your software doesn't let you do this, you need better!).

 

Obviously, if you're short of tracks and have to pre-mix the snare then you have to get it right to start with--I'd do this by ear rather than worrying about any perceived wisdom on the topic. However, any time you play with polarity please make sure you check the result in both stereo and mono...mono can often be a big problem with cancellation effects.

 

Bob

[Killyp]

I'd agree with Bobbsy. Even the most basic software packages I've used have allowed you to reverse polarity.

 

I often don't though, as I find sometimes it doesn't sound as good - particularly with side-sticks.