Mid-side stereo with Pro Tools?

[Kevin Windrem]

A plug-in seems like the way to go as it minimizes the complexity of the session.

The Waves S1 MS Matrix has no adjustments. However, the S1 Imager and S1 Shuffler have an M-S Input mode that produces a mathematically correct matrix with all controls at default. These are handy if the input signals are incorrect (swapped or phase reversed) or if you want to adjust the width of the stereo image.

The Waves manual for S1 has some very useful hints for working with M-S and other stereo signals. They even suggest converting an X-Y signal to M-S for "interesting" processing alternatives like different EQ on Mid and Side.

If you don't have a plug-in available, recording the M-S to a stereo track then using using aux tracks to build the matrix seems like the next best approach to avoid problems when editing tracks. As previously suggested, using a stereo aux for the side signal minimizes the number of things that need to be managed together. Just remember to keep delays matched (or use Delay Compensation).

Using two identical audio tracks for the side signal seems wasteful since they differ only in phase. Using Audiosuite for phase reversal means you can't monitor the Left-Right result until after the recording.

The Digi Trim plug-in also has phase reverse and might be a smaller footprint than the delay compensation plug-ins. It also will be included the Delay Compensation calculation where the delay compensation plug-ins will NOT. (If you add delay to a signal there must be a reason for it right?)

[kosi]

What about this one !

http://brainworx.h-is.de/index.php?nav=24&um=2&lang=en

[Steve MacMillan]

I love this thread.

I got a live show to mix a short while back, and the main room mics were M/S. First I tried the Waves decoder, but the image was all wrong. So I did the classic M mono up the middle, S split to two tracks panned wide, the right side flipped. When I brought up the sides tracks equally the image leaned way left. In order to get a left - right balance I had to boost the right side by 6 - 8 db and the center sounded hollow. I found a balance that worked, but I thought that either I was doing something wrong or the mics were not set up properly. Any ideas?

STeve

[BKR]

Yes on the Brainworx plug. I've reviewed it for an upcoming issue of Mix. Essentially a fantastic stereo mastering EQ that works on conventional stereo pairs AND also M/S signals that are converted into stereo. It has a couple of apparent loudness processors, a de-esser and many very cool GUI features. Well worth having even if you don't master.
Barry Rudolph

[kbruff]

Originally Posted by PTUser NYC

There's probably a plug in, but if you don't have one, you can still do it in Pro Tools. Even if you do use a plug in to actually do it, this discussion is useful to understand what M/S is.

SET UP THE MICS

For M/S recording you use two microphones, with their capsules very close to touching. The idea is to get them to be virtually in the same place, so their outputs will be very similar.

One mic is an omni or cardiod mic, and it faces the center of the stereo image of the sound source you are recording. If you want the source to end up in the middle of the stereo image, point the first mic right at it, if you were hoping to place something on the side, point this mic at the center of the image, which might be up to 90 degrees away laterally from the source, (left or right).

Imagine, for example, using a U87, hung, mounted with the capsule below the body, perpendicular to the floor, and rotating its "point of view" on a horizontal axis, like a camera panning left or right across the horizon. Point the mic at the center of the stereo picture you want to capture. This omni or cardiod mic is the "Mid" mic.

Now for the directional component. A second mic, which is bi-directional (figure 8 type) in nature is used. If the first mic was hung, then the bidirectional mic is right side up, so that the two capsules are as close as possible, one under the other. The bidirectional mic is set so that from a bird's eye view, looking down, the "front" of the bidirectional mic is rotated 90 degrees to the left (counter clockwise) of the center line the first mic is "looking" at. If the "Mid" mic is pointing North, then the bidirectional mic is pointing West, 90 degrees to the "left". This is the "Side" mic.

THE THEORY

At this point, lets consider what happens in each microphone.

When a sound comes from the front of the M/S pair, the Mid mic, (which is pointing right at it), records the sound as a "positive polarity" event. The compression side of each audio wave is causing the capsule to move backwards, and create a positive electrical voltage, the wave in Pro Tools goes up from the zero line. It will make the speaker move out toward our ears first when played, recreating the compression wave in the air that hit the microphone.

As happy as the Mid mic is, the Side mic gets very little of the direct sound here, because its null is pointing directly forward, since we set it up facing "hard left".

Add them together, and you get roughly just the mid mic. Not much from the Side mic.

Now imagine a sound source coming directionally from the leftish side of the array. It makes the same deal with the mid mic (especially if its in omni), but now the bidirectional mic is picking more of it up too. Since the bidirectional mic is pointing left, sounds from the left are being recorded as "positive polarity". The waveform in Pro Tools is going positively first, just like they did in the Mid mic.

Add them together and you get level from both. This time you get basically the same Mid mic performance, PLUS the now present Side mic. Since the capsules are very close together, and the resulting signals are very similar, the result is louder than the center recording was. Things to the left get louder!

Imagine the other situation - where the sound source is on the right hand side. Mid mic is still the same, "positive polarity", but the sound is now coming into the BACK of the bidirectional mic. Now, while the "sound" is still similar at both mics, the mid mic is recording the situation as a "positive polarity" event, but the bidirectional mic is seeing the sound BEHIND IT, and this means polarity inversion from its point of view. That means that the waveform will be very similar to the mid mic's signal, but just "upside down". Look at it in Pro Tools, and see it moves downward from the zero line. This is a "negative polarity" event.

Add these two signals together, and you can imagine that they would cancel eachother out to some degree. The resulting sound is actually softer than the centered recordingwas . This get SOFTER when they move to the right.

When you add the two mics together, everything gets louder as it moves left, and softer as it moves right.

Now imagine if you flipped the polarity of the bidirectional mic's track. Obviously the opposite effect would occur. Things to the left would now get quieter, as the opposite polarities cancel eachother out, and things would get loder as they moved to the right, and the two waves became coherent.

This is how M/S works. With the Mid mic track panned center, and the Side mic panned hard to the left, with a polarity inverted copy of the Side mic track (at equal volume to its upside down twin) panned hard right.

Now things on the left get louder in the left speaker, and things form the right get quiter in the left speaker AND things from the left get quieter in the right speaker, and things from the right get louder in the right speaker.

Stereo!

M/S DECODING IN PRO TOOLS

Put the mid mic on a single mono audio track.

Create two more mono tracks and put the bidirectional "side" mic on each of them.

Flip the polarity of the second side track with audiosuite.

Drag the two side mic audio files into a stereo track, and delete the now empty 2 audio tracks.

Now you've got one mono track with the Mid mic on it, and one stereo track with the Side mic on the left, and the polarity inverted Side mic on the right - all "hard panned" (Panned all the way to the left and right sides).

Bring up the Mid mic, panned center, and then bring in the stereo Side mic tracks to taste. As you bring up the volume of the Side mics, find the sweet spots where convincing realistic stereo images are heard. If the original levels were the same, -6db for the Side mics relative to the Mid mic is one good place to check.

Once you find a good relationship, group the two tracks so they always follow volume changes together, in the same perspective.

VAMP AND FADE

You can see that as the source moves to the left, it gets louder in the left side, and quieter on the right side at the same time, and vice versa for right located sources. We're just combining both of the mono experiments from earlier, and panning each result to one side.

This technique can generate VERY detailed and realistic pictures of instruments in space. It is especially good at capturing ambient sources with a lot of room, like drum kits, roomy amps, string and horn sections, anything where an organic sounding stereo picture of the space is called for.

One additional benefit is that when your mix is summed to mono, the two side mic tracks cancel eachother out, and the mid mic speaks for itself. This mono compatability is rare for most stereo techniques where phase intereference from the two sides of the image can thin a sound out or make it sound comb filtered and plastic when it gets summed to mono.

Sorry for opening up such an old post, but surely I really enjoyed this thread. I Google searched Mid+Side+Processing in Pro-Tools and this thread was reported.

[[email protected]]

I have used an aux bus to duplicate the S signal, then add a 1 band EQ on ALL THREE signals (M + both ch on the S bus). Then flip the phase on the right ch aux EQ.
This way you don't have to duplicate any audio, and with the three plug-ins you ensure phase linearity.
The M signal is then panned to center, and the two others left + right.
By placing the M channel in between the two S channels you get a very logical view and you can adjust the stereo width with the (grouped) S channels...

OR You can get a Soundfield mic and the TDM Plug in to go with it!

[danander11]

PTUser NYC,

Thanks! Even I could understand that...

[midnightsun]

You can also convert a recorded stereo track from L-R to M-S in order to widen the stereo field.

[maxcarola]

There are a number of plugins for MS encoding and decoding.
brainworx has "control" in rtas and tdm versions. Waves has one S1.
But for me the most interesting is in the steven massey plugins (the free bundle)

M