Is double snare micing necessary?

[bouldersoundguy]

I've known saying phase' and meaning polarity' is vague and/or unspecific, but is it technically incorrect to say 'phase inversion- ?

I would say so. If a pair of waves is 180° out of phase it is only that at one frequency. At other frequencies it's different amounts out of phase, so the term "phase inversion" doesn't have much use. If it's being inverted it's polarity, not phase. If it's shifted or rotated it's phase. Both can cause cancellation, but polarity's effect is equal across the spectrum while phase's effect is frequency dependent.

 

[Steenamaroo]

i always assumed people just know this, and it's only a common mistake cos manufacturers usually call it "phase reverse" or "phase invert"

 

[Farview]

So when Doctor Who talks about polarity, I should just make a fist of rock and yell rock on?

If you are trying to glean technical knowledge by watching Dr. Who, that's a problem.

Sure, polarity if you're talking about PRE-recorded tracks. But post recorded tracks? When dealing with the resultant data, not the signal chain. i.e. Two tracks (top and bottom) to be mixed.

You are missing the point. Phase is (generally) a timing difference between a frequency(s) in two signals. A polarity difference is when one wave is going the opposite direction of the other it is being compared to.

Polarity to me has always been an electronics term. And I guess that if you're tweaking the electronics with a modified cable that would apply. But I don't do anything that involves outputting sound live. It's all just captured data to be mangled later in my case.

It makes no difference if you do it electrically or you are working with digital representations of waveforms, it still works the same. Besides, in order for you to hear it, it has to be turned back into real electrical waveforms to run the speakers.

 

[grimtraveller]

I record the bottom of the snare, phase reversed, sometimes with an sm57, sometimes with an MD421. I never use the bottom track.

Just out of interest, why do you never use the bottom track if you go to the trouble of miking the bottom of the snare ? I ask because 'never' is pretty inflexible.

 

[witzendoz]

I record the bottom of the snare, phase reversed, sometimes with an sm57, sometimes with an MD421. I never use the bottom track. I record the top of the snare with an sm57 about 1/2" above the edge of the rim pointing towards the center of the snare, always tend to boost highs and add lots of reverb.

Actually none of this made any sense? Why would you need to add lots of reverb? The music may not suit lots of reverb?

Talking about phase, polarity etc etc, well you flip the phase on the bottom mic, if there is a slight out of phase problem due to it not being exactly 180 deg with the top mic, well just move it further away or closer to the snare, this adjusts the phase. Why de we get so scientific? If it sounds good it is good, if it doesn't change it.

alan.

 

[bouldersoundguy]

Talking about phase, polarity etc etc, well you flip the phase on the bottom mic, if there is a slight out of phase problem due to it not being exactly 180 deg with the top mic, well just move it further away or closer to the snare, this adjusts the phase. Why de we get so scientific? If it sounds good it is good, if it doesn't change it.

This is a good example of the confusion between phase and polarity.

If two mics are different distances from one source their signals will be out of phase. How much depends on how different the distances are and at what frequency you measure it. In other words, "180°@2kHz" or the like. But at other frequencies it will be out of phase by different amounts, proportional to frequency, e.g. 360°@4kHz, 90°@1kHz and 45°@500Hz. At 2kHz there will be total cancellation of the signal (assuming identical signal level). Inverting polarity doesn't change the phase error, it simply makes it act as if it were 180° around the cycle. In the above case 2kHz would then act like 0° but 4kHz would act like 180°, so it's really just moving the problem frequencies around. Polarity inversion cannot prevent phase cancellation at one frequency without causing it at others.

The case of top and bottom snare mics is one of polarity and phase. The polarity discrepancy comes from the two mics being on opposite sides of the head. What is a positive pressure wave on the top of the head is a negative pressure wave on the bottom. The phase difference comes from the fact that the bottom mic is farther than the top mic from the top head, so it's delayed by a large fraction of a ms. A simple polarity inversion solves the polarity mismatch but doesn't address the different distances of the two mics. Fortunately the signal is so altered and added to by passing through the bottom head and snares that phase becomes a non-issue.

 

[guitaristic]

Guys, why get so confusing.

Flip the thingy. Don't flip the other thingy.

That's my motto.