MS stereo asymmetry

[The Listener]

Originally Posted by John Willett

OK...................................


So - polarity reversing the fig.8 means that the rear lobe becomes the front lobe for the right mic.

Thank you, mystery solved for me by this analogy.

[The Listener]

Originally Posted by ghellquist

It is not too difficult to understand really.

Assume that we have a perfectly good M mic (any type really, but I will use an omni as example to simplify things)

Assume that we have a really bad S mic that is more or less deaf towards right. It can only hear things to the left. This is of course extreme, in the real world it might only dampen things by say 10dB, but that is enough to skew the stereo panorama.

The two signals from the mics are called M and S.

The operation we do in decoding is described by a very simple mathematical formula.

L = M + S
R = M - S

Now we put a source all the way to the left. Remember that the signal will be heard both by the omni M mic and the faulty S mic. Lets keep things really simple and say that the signal from both mics is 1Volt.

What we get is:
L = M + S = 1 + 1 = 2
R = M - S = 1 - 1 = 0.
So clearly this signal is heard fully panned left.

Now we put the source to the right instead. Remember that the S mic in this is example is deaf to the right so the signal from that one is 0.
L = M + S = 1 + 0 = 1
R = M - S = 1 - 0 = 1
So clearly this signal is heard panned straight in the middle. The faulty S mic has destroyed the panning as things will only be panned in the middle or to the left, never to the right.

Small note: if the S mic had been working as a figure 8 the signal would have been -1 Volt, fully out of phase with the M signal. In that case we get:
L = M + S = 1 + (-1) = 0
R = M - S = 1 - (-1) = 2
which gives us the expected full pan to the right.

Hope this simplified example helps. Not meant to be the full details.

// Gunnar

[baslotto]

To the OP.
Did you end up sending the mic back for service? There is clearly something wrong with it.
By the way, from the samples it's a hell of a mic!

Keep us posted.

[7rojo7]

I'd rather use the UM70 in omni and find a good fig 8 for the sides
I dislike MS it has its uses, butdfegad
on close micing instruments I use xy, MS has no detail for me, sounds like an effect
I can only imagine disappointment on laying a bunch of MS tracks one atop another
MS was originally devised by Alan Blumlein with an omni M and a figure 8 S to control the pattern of that array, it has it's uses, I don't believe that multitracking could be one of them. For Broadcast they started using cardioids as the M and this has found its way everywhere by now.
You have much more control over the image in xy (for multitracking) and the same number of channels
I don't understand everyone's fascination for MS, the S signal disappears in mono leaving you with a cardiod, which in essence should be an omni, and a pile of manure in mono if you don't get it just right, and it's never an accurate image of whats happening, but it's not bad as an ambient array about 30 feet back hung from the rafters, I would still use an xy or a distant AB (more to measure) there
There's someone who's using 3 (or 4 maybe, I forget) MS arrays in a DECCA tree type of thing, but this is to control the pattern of the array
I was fascinated at the beginning with MS and Blumlein, but after a while they sounded like effects and not STEREO
Josephson has a mono and a stereo version of the same mic that approaches this in a very intelligent manner, I haven't heard it but I've experimented with arrays that use these principals and have had a modecum of sonic success, the Soundfield also has 4 capsules and various ways to encode/decode
I like to keep it simple L is L and R is R, if there needs to be a center then C is C
Critical distance, inverse square and proximity effect already keep me pretty busy
I've never heard a ribbon that was equal front to back, I put a little red dot on mine to point them, there is definitely a difference, I would only use Blumlein with C24 or U69, SM2 or the like because they have continueously variable patterns and the ribbon fig8 is too tight and leaves you with a center that's a mix of 2 off axis signals, blumlein was first used as MS anyhow

[The Listener]

I didn't send it to repair yet... I made contact and got the address where to send it. I am in the middle of a project and still need to record some vocals and percussion, but have only one UM70.

I was also thinking - since it is a vintage mic - maybe that's normal, and that almost perfectly identical response on both sides is maybe something that only modern version have.

About MS - in multitracking applications I really like it for acoustic guitars and similar. I had no problems stacking several MS sounds together. I pan them as stereo groups - with some stereo filed shifter - if I pan them at all...

One clip of raw MS acoustic guitar recording with SM81 cardioid and UM70 figure 8: MS guitar


btw - my weapon of choice for ambience recordings is ORTF.