M/S Technique - Simulating a Bidirectional Mic w/Two Cardioid Mics

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rj-skelton

New member
Hi there,

Apologies if this question has been answered elsewhere. I want to be able to track using the Mid/Side technique, but I can't afford to buy a new (bidirectional) microphone. I want to try and simulate the "side" microphone (which I understand should be bidirectional) by placing the diaphragms of two cardioid condenser microphones directly on top of each other, facing in opposite directions.

My question is: do I need to reverse the polarity of one of the cardioid mics?

My understanding is that in a bidirectional microphone, the polarity of the sound wave hitting the back of the diaphragm is (by design) automatically reversed, so that it is in phase with the sound wave hitting the front, but I could be completely wrong about how a bidirectional microphone operates.

I just want to confirm if this is the case?

Thanks if you can help
 
Yes, you need to reverse the polarity of one of the mics in order for it to work as MS. In your situation, you will pan the two side mics away from each other and reverse the polarity of one of them. The mid mic panned center.

It's not going to work exactly right, because the point of MS is that it will collapse perfectly to mono because the side mic will cancel out, leaving only the mid mic. Since you can't get the diaphragms close enough, they won't cancel completely.
 
Farview said:
Yes, you need to reverse the polarity of one of the mics in order for it to work as MS. In your situation, you will pan the two side mics away from each other and reverse the polarity of one of them. The mid mic panned center.
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But won't he just reverse the polarity again during m/s processing? I guess if he is using an outboard m/s processor, he needs to reverse it, but if he is processing in his DAW with three tracks, he shouldn't reverse it.
 
This is a funky thought experiment. I may have overthunk it...because you actually need a figure 8 pattern in order to use this method.

Now that I think about it, there is no need to reverse either of them. The only reason you reverse the mult of the side mic is to get the back diaphragm out of phase with the front one. There is no need when you use two separate mics.
 
rj-skelton said:
My understanding is that in a bidirectional microphone, the polarity of the sound wave hitting the back of the diaphragm is (by design) automatically reversed, so that it is in phase with the sound wave hitting the front, but I could be completely wrong about how a bidirectional microphone operates.
Click to expand...

And I just want to add that this is not the case. A figure-8 mic does not flip the phase on anything. It only produces one signal, not two. Not quite sure what mic you refer to when you say bi-directional.

If budget is a problem, look at the Studio Projects B3. It's not terribly expensive as multi patterns go.
 
You have the mics for an X-Y array. Just do that.

But if you're bent on trying it you won't want to invert the polarity of a side mic [Edit: not correct], but then you also won't get the null needed to make M-S work right. It may be an interesting or useful array but it won't be M-S.
 
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Chili said:
And I just want to add that this is not the case. A figure-8 mic does not flip the phase on anything. It only produces one signal, not two. Not quite sure what mic you refer to when you say bi-directional.

If budget is a problem, look at the Studio Projects B3. It's not terribly expensive as multi patterns go.
Click to expand...

Multi pattern condenser mics use two diaphragms back to back. They get the different patterns by combining them different ways, running one with inverted polarity to get figure-8. There may be only one output but there are two signals inside the mic.
 
bouldersoundguy said:
Multi pattern condenser mics use two diaphragms back to back. They get the different patterns by combining them different ways, running one with inverted polarity to get figure-8. There may be only one output but there are two signals inside the mic.
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Cool. Learned something new. I always thought the 2nd diaphragm was turned off for figure 8.
 
Yeah, Farview was right to begin with. You're going to combine the two side mics (one inverted) into the S channel. When this gets decoded to stereo you'll have that (SL - SR) panned left, and the inverse of that (SR - SL) panned right.
 
It depends if you are using a decoder or doing it manually. If you are doing it manually, with 3 tracks, the two side mics need to simply be panned apart.

(The decoder Mults the side mic, pans them wide, and inverts one of them)
 
This is going to work less tha ideally - because it the differences in phase that creat the width, and as your two cardioids cannot occupy thye same physical space, there will be phase errors in your reconsituted bi-directional channel - which will make a mess of the matrixing with the mid channel. These phase issues will also be frequency dependent, so you could easily find the apparent sound location changes rapidly as the sound source goes through it's register. Expect weird comb filtering and a 'hollow' sound from the two mics competing against each other.
 
Thanks for the input guys

I know what im trying to do is not ideal and for a true m/s array I would use a figure of 8 mic, and yes I know I can use X/Y instead, I just wanted to experiment. I got the idea from a talk I found on youtube by Steve Albini on recording drums where he said you could fake a figure of 8 mic using two cardioid mics.

It was interesting what bouldersoundguy said about multi-pattern condenser mics having two diagphragms to create the different polar patterns, because isn't that essentially what i'm doing with the two cardiod mics? (granted its not identical because I'm not going to be able to get the diaphragms as close to each other as they are in a single mic).

I'll give some more detail on how I thought I would do it. I'd be treating the two cardioid mics as if they were one figure of 8 mic (panning them both left in my DAW), then simply duplicate those two tracks, pan them right, and flip the polarity on both of them. I then have a third cardioid mic (a different one in my case, large diagphragm) panned centre.
 
This is what I was saying. If you are doing it manually, you don't need to copy the side tracks and invert them.

The reason for doing that with the figure 8 mic is to separate the left side from the right side. Since you are.using two different mics, you already have that separation.

BTW, have you heard or worked with any of Albini's drum sounds? Everything I've come across is a mess of phase and wierdness.
 
Farview said:
It depends if you are using a decoder or doing it manually. If you are doing it manually, with 3 tracks, the two side mics need to simply be panned apart.

(The decoder Mults the side mic, pans them wide, and inverts one of them)
Click to expand...
This is not the same thing at all. Two cardiod mics "back to back" like this will act like an omni, and they won't leave the null area where the mid mic is supposed to fill in. It will be some sort of stereo, but it won't be M/S. You absolutely need the two side mics to cancel out any information that they share. Doesn't matter how you're decoding the M/S.
 
Hmm, you've got a point there. The cardioids have side lobes where the figure 8 has none. Without inverting one side mic, that region would be additive and in the same axis as the mid mic. Maybe invert the mid mic to cancel out one side lobe.

If I wasn't so busy with other projects, I'd experiment with this.
 
Chili said:
Hmm, you've got a point there. The cardioids have side lobes where the figure 8 has none. Without inverting one side mic, that region would be additive and in the same axis as the mid mic. Maybe invert the mid mic to cancel out one side lobe.

If I wasn't so busy with other projects, I'd experiment with this.
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Then you've got no mid at all!


Invert one of the side mics. Mix the two of them together into a new mono channel/track. Treat that new track exactly like a single figure 8.


!!!!
 
I've never worked with his drum sounds, I'm a complete amateur I only work with my own stuff. I've heard surfer rosa by the pixies and the Albini mix of in utero, I've also heard some shellac stuff. I dunno to me they sound great, but Albini has quite a different attitude to recording than a lot of people in the industry and I don't know how he records drums, other than that short clip on YouTube I mentioned
 
rj-skelton said:
I've never worked with his drum sounds, I'm a complete amateur I only work with my own stuff. I've heard surfer rosa by the pixies and the Albini mix of in utero, I've also heard some shellac stuff. I dunno to me they sound great, but Albini has quite a different attitude to recording than a lot of people in the industry and I don't know how he records drums, other than that short clip on YouTube I mentioned
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Check out PJ Harvey "Rid of Me". IMO, he went way too far with the "no compression ever" thing on this one, and I always use it as an example of how too much dynamic range can be a bad thing (try to listen to it in a car without going back and forth to the volume knob at every verse/chorus transition), but it's a pretty fucking great album.

I've actually got a project I'm about to start working on that was recorded at Electrical, but I haven't even listened to a single track yet.
 
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