Topic: V2/3 M-S matrixing Questions and observations

[Nick's Picks]

hey now sport tapers...

I've got an observation that has formed a question.
I've set the internal jumpers in the V2 or V3 for Mid Side (vs. stereo) on a number of occasions for some recording projects.
As I understand it, this is supposed to do the matrixing internaly and output a stereo signal.

w/the jumpers set you end up with:

left = mid
right = side

adjusting the gain on the right is adding width (side information) and adding gain to the left brings more mid (front) info.
Typicaly, I'd set my level on the left and leave it be and then dial in the ammount of side volume I felt was the best mix for the given situation.

My observation is that when i've done this, I notice that the louder I turn the "width", the louder the right channel becomes and I end up with lopsided wav files (one side channel louder)
yet, when I monitor w/headphones while doing it, i can clearly hear the addition of side information when I turn the gain knob up.

Now, shouldn't this "side" information be distrubuted equaly over both channels if in fact the Grace unit is doing the M-S decoding internally? It just doesn't seem right when I look at the .wav files in software. One is always louder than the other, and this shouldnt be the case.

What am I missing here?

[Brian]

are you sure your jumpers are set correctly.  joe shambro opened up his the other night.  i could see how only one could be in the wrong spot.

thanks for looking into this. i would like to run M/S soon without having to hassle with the post production work if i don't have to since i have a v2.

i'm currently also customizing my HPF's in the v2 as well. this pre rocks!

Brian

[Nick's Picks]

very positive about the correct jumper settings.
the manual has nice pictures.  I think the other ones that you can see right off have to do w/phantom settings and the -20db line level pad on the front end.

but i'm sure about which jumpers are which.

[nic]

Nick, are you switching both jumpers(1 set for each channel)?
I'm looking at the V2 manual, and there are 2 sets of jumpers you need to move for stereo vs m/s

[Nick's Picks]

yes.
I followed the instructions to the T.  
I no longer have any Grace products, but when I did...i did plenty of M-S recording w/them.  Its not a big deal to set the jumpers.   I'm not trying to get all pissy, but let us just assume i did it correctly instead of all the 2nd guessing.  I can read a manual as well as the next guy!

Try it out, you'll see what I mean about the way it works and distributes gain.

[Tim]

hey Nick,

Most engineers I know prefer to decode to stereo after the fact. That's really what M-S is all about - perfection in the stereo image via post production . Consider giving it a try, perhaps record your stereo for the test.

[Nick's Picks]

yea yea ... I know

you can do it pretty effectively on the fly w/Etymotics.

[Tim]

I was just busting your balls, I got a kick out of that post over on oade, I just copied and pasted it here to taunt you.

I'm interested in hearing what you find out. I sure would like to start doing some M/S work but I'd prefer to do it in the field.

[Nick's Picks]

bastard!
I knew it was the same post, but from someone else.
taunted me good, you did!

[dklein]

What mics are you using?

[carlbeck]

Nick, it doesn't really matter. I'm not letting you use my V3

[Nick's Picks]

You can keep it, HONKY!
I'll do it in post "like i'm supposed to"

for M-S recording in the past i've used the AKG c422 and the Soundfield ST-250

[dklein]

for M-S recording in the past i've used the AKG c422 and the Soundfield ST-250

I've never tried m-s before but it's a card for the mid and figure-of-eight for the side, right?  I asked about the mics because I could see how using the wrong polar pattern for the side mic would cause that effect.  e.g. if the side capsule was set to card, increasing the side levels would be additive on one channel and subtractive on the other (creating a level difference).  Just a thought...you've obviously got the experience.

[dklein]

having some fun with mic theory and algebra....
the mid card is (R+L)
the side figure of 8 is (R-L)

m-s decoding takes the side and feeds the straight signal to the right and the inverse signal to the left (the absolute polarity depends which way your figure of 8 is pointing).

Your two channels are:
card + fo8
card - fo8

(R+L) + (R-L) = 2R
(R+L) - (R-L) = 2L

And that's where the left and right come from.

If you were to swap the mid and side (i.e. plug the card into the side and the fo8 into the mid) then the m-s decoding process would do this:

fo8 + card
fo8 - card

(R-L) + (R+L) = 2R
(R-L) - (R+L) = -2L

2 catches:
First - the notion of +/- is really about phase.  A +1 and a -1 are the same 'loudness'.
Second - the above simple algebra assumes equal strength signal when in fact you use much less side.  If side was at 50%, you'd end up with:

1.5R / 0.5L = absolute signal level of 2.0
0.5R / -1.5L = absolute signal level of 1.0

That would explain why turning up the side channel causes the level difference between left and right.  It seems that the more you dial up the side, the more the left will drop.  

Nick - it might be worth swapping the mid / side into the preamp and seeing if you get even gain in both channels as you turn up the side.  That would prove it.

david (living in the world of theory)  

[dklein]

c'mon Nick - what's the scoop?  Inquiring minds want to know.

If that algebra above is correct, your left and right should also be out of phase.  If you sit in a proper listening spot with speakers and play with the balance control, you should hear more bass with only the left, or only the right.  Less bass when both speakers are running.

[Nick's Picks]

unfortunately, i'll have to leave this up to someone else to try as i no longer have a Lunatec preamp to test this on.

I brought this up 6mo too late, i'm afraid.

[Brian]

well i was going to run M/S for RW20C this upcoming weekend until I found out he does not allow stage taping anymore. i run tl>v2>modsbm1 and was eager to try out the M/S matrixing with the V2.

i have to find a a REALLY good jazz band that plays weekly around here so i can try this out.

Brian