A funny thing about Mid/Side

Recording Techniques, People Skills, Gear, Recording Spaces, Computers, and DIY

Moderators: drumsound, tomb

Post Reply
cale w
gettin' sounds
Posts: 145
Joined: Mon Nov 09, 2009 12:15 pm
Location: Seattle

A funny thing about Mid/Side

Post by cale w » Sat Feb 18, 2012 9:29 pm

So the other night I set up in my practice space and recorded myself playing some electric guitar and singing. I was sitting centered against one wall, singing into the room at a PR40. The guitar amp was on the opposite wall blowing towards me and into a close 57. In between the two sound sources I had a Fathead as a room mic with the amp and my voice in nulls, probably 6 feet away from both the voice and amp. When I was mixing, out of curiosity's sake, I duplicated the room mic, hard panned the copies and flipped the phase on one... and suddenly, the information from the Fathead was in stereo, just like a M/S setup. I'm a little perplexed because I always thought in a traditional M/S setup, the mid information had to come from a mic in coincident with the side mic. So I guess the side mic was taking information from from two far away (but close on sound source) mics and sorting out the L/R reflections into real stereo. My mind was a little blown, but maybe it shouldn't be so surprising? Has anyone else ever experimented with this?

User avatar
vvv
zen recordist
Posts: 8615
Joined: Tue May 13, 2003 8:08 am
Location: Chi
Contact:

Post by vvv » Sat Feb 18, 2012 10:37 pm

Yep.

When you say, "in a traditional M/S setup, the mid information had to come from a mic in coincident with the side mic", the operative word may be "traditional", and it's that for predictability and control.

As I understand it, duping and flipping the room mic (which, BTW, need not even be figure 8) gives you the two tracks against which you are using whatever "mid mic", and whatever cancellation/reinforcement you get by changing their levels.

One big difference is, when you collapse to mono, the change in sound is going to be much different, as the mid mic is so much different from the side mic tracks.

In your reported case, I wouldn't be surprised if there is a an M/S effect involving both of the other mic's.
bandcamp; vlayman;
THD; Geronimo Cowboys;
blog.
I mix with olive juice.

Professor
ghost haunting audio students
Posts: 3307
Joined: Wed May 07, 2003 2:11 pm
Location: I have arrived... but where the hell am I?

Post by Professor » Tue Feb 21, 2012 12:59 pm

A lot of stereo processors that try to take a single channel and make it sound more stereo will play with duplicating the track, flipping phase, and introducing a tiny bit of delay to one side. When you think about it you're not too far off from that... sort of.

You have a room mic in Fig-8 that you're copying and inverting, but it's further away from the two sources, so it's delivering the sound a tiny bit later and at a lower volume.
You also have two close mics that are catching the voice and the guitar and delivering them earlier and with less room.

As always, the golden rule is that if it sounds good then you should keep it. If you want to play around and see how you can push the setup to deliver something different, here are some things to try:
1- Mute the guitar "Mid" mic and put a tiny bit of delay (corrective, not a looping delay) on the vocal "Mid" mic. Adjust it to compensate for the time difference between it and the room - about 0.9ms per foot between them.
2- Then try it the other way around. Mute the vocal mic and time-align the guitar mic to the room.
3- Then try everything together with the new arrangement and bring the volume level of the room mic (and copy) up and down in the mix to see how the sense of space changes and what kind of sound you like.

I don't know if any of those will sound better, worse, or like nothing at all... but it's worth experimenting. My guess is that the sound will tighten up and seem more focused when the delays are in place, but it's only a guess.

If you have a scope or plug-in of some variety (like the Phase Scope plug-in in Pro Tools) then set it on your mix bus so you can see how the phase is behaving as you experiment. That plus lots of switching between stereo and mono monitoring should keep you safe.

-Jeremy

User avatar
rhythm ranch
mixes from purgatory
Posts: 2792
Joined: Wed May 07, 2003 8:45 pm
Location: Corrales, NM

Post by rhythm ranch » Tue Feb 21, 2012 1:15 pm

Professor wrote:Jeremy
WOW! Welcome back Jeremy! Haven't seen you on the board for a while. I always appreciate your insightful posts.

Professor
ghost haunting audio students
Posts: 3307
Joined: Wed May 07, 2003 2:11 pm
Location: I have arrived... but where the hell am I?

Post by Professor » Tue Feb 21, 2012 1:17 pm

Aww, thanks.

Wasn't sure anyone would notice if I slipped in the back door all quiet-like and stuff. Will try to be around more regularly with helpful tips and crazy tales from the road.

-Jeremy
In a strange twist of fate, portions of my brain are now available in book form from Cengage Course Technology:
Mastering Pro Tools Effects

Cyan421
takin' a dinner break
Posts: 192
Joined: Sat Nov 05, 2005 3:56 pm
Location: Idaho (On The Causeway to Neverwhere)

Post by Cyan421 » Tue Feb 21, 2012 1:50 pm

very nice to see you back professor!
"What a wonerful smell you've discovered"

Post Reply

Who is online

Users browsing this forum: No registered users and 12 guests