Ms-Stereo - Some help????

[carlosff17]

Hi!

I'm a student at cinema college, and I'm just starting to shoot a 35mm short film, and i would like to record the ambiences, (when the camera is off) with this stereo technique (MS-Stereo)! My doubt is just the following... I have a cardioid and a bi-directional, but, i have to invert one phase of the bi-directional microphone, isn't it? then, my mixer haven't that option, so i figure it out some other way to do it...

What about that if i connect the microphone to a microphone pre-amplifier, then in the output, i use 1 split xlr cable which will divide in 2 signals, the the left, i connect to the mixer and turn the pan left, and the other one, the right, i have to connect to other device which could invert the phase and just after that i can connect to the mixer and pan it to the right...

My doubt is, what could be that device? I really need it...it´s urgent.

Thanks,

Carlos Faustino

 

[BRH]

Forget about it. Use the same mic you are using for dialog. Create stereo in post.

 

[10s]

If you're just starting to shoot a 35mm film and you don't have this worked out, that makes me question what else is missing. Answer to question: Get a fellow student who is an audio guy to help out. If not, postpone the shoot until you get this sorted out.

Below is from Wikipedia:


Normal stereo recording uses 2 matching mics set up in a few accurate configurations to avoid phase cancellation. This info availble all over the place on-line. The two mics connect to 2 channels, etc.

Recording methods

[edit] X-Y technique: intensity stereophony


X-Y Stereo Microphone placement


Here, two directional microphones at the same place, and typically pointing at an angle between 90° and 135° to each other — see also "The Stereophonic Zoom" by Michael Williams. A stereo effect is achieved through differences in sound pressure level between two microphones. The level difference of 18 dB (16 to 20 dB) is needed for hearing the direction of a loudspeaker. Due to the lack of differences in time-of-arrival / phase-ambiguities, the sonic characteristic of X-Y recordings has less sense of space and depth when compared to recordings employing an AB-setup. When two figure-of-eight microphones are used, facing ±45° with respect to the sound source, the X-Y-setup is called a Blumlein Pair. The sonic image produced is realistic, almost 'holographic'. See also Acoustic intensity.

[edit] A-B technique: time-of-arrival stereophony


A-B Stereo Microphone placement


This uses two parallel omnidirectional microphones some distance apart, so capturing time-of-arrival stereo information as well as some level (amplitude) difference information, especially if employed in close proximity to the sound source(s). At a distance of about 60 cm (0.6 m) the time delay (time of arrival difference) for a signal reaching first one and then the other microphone from the side is approximately 1.5 msec (1 to 2 msec). If you increase the distance between the microphones you effectively decrease the pickup angle. At 70 cm distance it is about equivalent to the pickup angle of the near-coincident ORTF-setup.
This technique can produce phase issues when the stereo signal is mixed to mono.

[edit] M/S technique: Mid/Side stereophony


MId-Side Stereo Microphone technique


This coincident technique employs a bidirectional microphone facing sideways and another microphone (generally a variety of cardioid, although Alan Blumlein described the usage of an omnidirectional transducer in his original patent) at an angle of 90° facing the sound source. The left and right channels are produced through a simple matrix: Left = Mid + Side, Right = Mid - Side (the polarity-reversed side-signal). This configuration produces a completely mono-compatible signal, and if the Mid and Side signals are recorded — rather than the matrixed Left and Right — the stereo width can be manipulated after the recording has taken place, which makes it especially useful for the usage on film-based projects.
[edit] Near-coincident technique: mixed stereophony


ORTF Stereo Microphone technique


These techniques combine the principles of both A/B and X/Y (coincident pair) techniques. For example, the ORTF stereo technique of the Office de Radiodiffusion Télévision Française (i.e., Radio France), calls for a pair of cardioid microphones placed 17 cm apart at a total angle between microphones of 110 degrees that results in a stereophonic pickup-angle of 96 degrees (Stereo Recording Angle SRA).[2] In the NOS stereo technique of the Nederlandse Omroep Stichting (i.e., Holland Radio), the total angle between microphones is 90 degrees and the distance is 30 cm, so capturing time-of-arrival stereo information as well as level information. It is noteworthy that the spacing of 17 cm has nothing to do with human ear distance. The recorded signals are generally intended for playback over stereo loudspeakers and not for earphones.

 

[DavidNJ]

Doesn't M/S require a figure-8 mic and Blumlein require two figure-8 mics (4 cardioid cartridges). Also, aren't they usually done with studio mics significantly different that the small diaphragm condenser mics we typically use?

 

[Steve House]

Doesn't M/S require a figure-8 mic and Blumlein require two figure-8 mics (4 cardioid cartridges). Also, aren't they usually done with studio mics significantly different that the small diaphragm condenser mics we typically use?

Not quite. A figure-8 mic is not a pair of cardioids, it is a single diaphram, dipole transducer mic with its axis of sensitivity transverse to the mic body axis. It's usually marked with an indicator of the axis and the positive phase direction. While there are large diaphram studio mics with a figure-8 pattern, a number of small diaphram types are also around. A classic very high quality setup, for example, could be made up of a pair of Schoeps CMC series mics, one with a MK4 cardioid capsule and the other with a MK8 figure-8 capsule. In fact, this is a common setup in European feature and broadcast production and Schoeps makes a shockmount and blimp to hold just such a pair on a boompole. Another good combo at a much lower price is a pair of AKG Blueline mics, one with a CK91 cardioid and the other with a CK94 figure-8 capsule.

Carlos, if you can forgo stereo monitoring in the field you don't need to worry about whether your mixer decodes or not, nor do you need to jury-rig splitters etc. Just record the M/S mic pair as if it were a normal stereo pair, putting the cardioid mid mic on what is normally the left channel and the figure-8 on what is normally the right. Back in post you import the file into your DAW and split the two channels into two mono tracks, the left becoming the mid track and the right the side. Copy the side track to a third track and invert its phase. This is a straightforward menu choice in most DAW such as Soundforge, Vegas, or Adobe Audition. Set up your mix so the mid track plus the side track goes to the left output channel and the mid plus the inverted side track goes to the right.

One advantage of recording the raw mic channels and dematrixing in post rather than dematrixing them in the field and recording the resulting stereo directly is that you can use plugins like the Waves S1 Stereo Spatializer in post to get a lot of control over the final result.

 

[John Willett]

Hi!

I'm a student at cinema college, and I'm just starting to shoot a 35mm short film, and i would like to record the ambiences, (when the camera is off) with this stereo technique (MS-Stereo)! My doubt is just the following... I have a cardioid and a bi-directional, but, i have to invert one phase of the bi-directional microphone, isn't it? then, my mixer haven't that option, so i figure it out some other way to do it...

What about that if i connect the microphone to a microphone pre-amplifier, then in the output, i use 1 split xlr cable which will divide in 2 signals, the the left, i connect to the mixer and turn the pan left, and the other one, the right, i have to connect to other device which could invert the phase and just after that i can connect to the mixer and pan it to the right...

My doubt is, what could be that device? I really need it...it´s urgent.

Thanks,

Carlos Faustino

Hi Carlos,

I record MS a lot.

Your best option is to record the mid mic. (cardioid) on the left channel and the side mic. (fig.8) on the right.

Make sure the +ve lobe of the fig.8 is pointing to the left.

Then do the MS matrixing in post - Voxengo do a great free MS plug-in for this - you get it HERE.

And - for anyone who already has the plug-in, this links to the new, recently released, improved v2.

 

[John Willett]

Not quite. A figure-8 mic is not a pair of cardioids, it is a single diaphram, dipole transducer mic with its axis of sensitivity transverse to the mic body axis.

Yes and no - I only know of three single diaphragm condenser fig.8 mics.:- Sennheiser MKH 20, Neumann KM 120 and the Schoeps. All the others are made up from back-to-back cardioids.

 

[John Willett]

Doesn't M/S require a figure-8 mic and Blumlein require two figure-8 mics (4 cardioid cartridges). Also, aren't they usually done with studio mics significantly different that the small diaphragm condenser mics we typically use?

The small fig.8 mics. most used are the three I mentioned in my post above - all these are small pencil type mics.

 

[Noiz2]

To answer the original post, well part that hasn't directly been addressed. You don't mess around with phase when you record. The phase inversion happens when decoding the M/S signal.

If your recording backgrounds definitely record them in stereo. You will create the environment in post but that environment will be better and fuller with stereo BG's. And in general you don't want to be using the same mic you used for dialog. If your picking up room tome then by all means use the same mic but if your recording backgrounds stereo and a pair of cardioids, or the M/S setup is a better choice. Also to be of much use in post you need at least a full minute of clean BG, three minutes are preferred. So don't use a heavy mic setup or your arms are going to be killing you.

 

[Steve House]

Yes and no - I only know of three single diaphragm condenser fig.8 mics.:- Sennheiser MKH 20, Neumann KM 120 and the Schoeps. All the others are made up from back-to-back cardioids.

AKG Blueline CK94 as well, I'm pretty sure that's a single diaphram capsule. Actually any pressure-gradient transducer's baseline pattern is figure-8. Then there's the variable pattern large diaphram models like the AKG C414 - single capsule, dual diaphram. I suppose you could say that that is technically a back-to-back pair of cardioids but that term makes me think of two separate cardioid mic capsules facing opposite directions like that T-shaped Oktava adapter or even two separate pencil mics on a stand that points them in opposite directions.

 

[carlosff17]

Thanks to all

Thanks to all

Well, thanks to all the repplies.

However, i figured out a new possible way to do it.

Using a mixer. So, recording the cardioid directly to the mixer to channel 1 for example...the, the fig.8, connect it directly to the mixer, and turn the pan to the left, the with a jack/xlr do a "direct-out" and in the end of the cable, the xlr connection, connect then an "mini"-xlr with the 2-pin inverted, and again, connecting it to other xlr/jack to the other channel of the table, directly on line, and turn the pan to the right....

I think this could probably works.

 

[Steve House]

Well, thanks to all the repplies.

However, i figured out a new possible way to do it.

Using a mixer. So, recording the cardioid directly to the mixer to channel 1 for example...the, the fig.8, connect it directly to the mixer, and turn the pan to the left, the with a jack/xlr do a "direct-out" and in the end of the cable, the xlr connection, connect then an "mini"-xlr with the 2-pin inverted, and again, connecting it to other xlr/jack to the other channel of the table, directly on line, and turn the pan to the right....

I think this could probably works.

The cardioid equally to left and right I presume. Might work, but why bother?Why not do it the old-fashioned way ... record the cardioid on the left channel, the figure-8 on the right, and do the conversion/mix to stereo in post? I can't see any advantage at all of doing the way you suggest, there are too many areas where problems could occur and if you're only recorded the resulting mix, there'll be no going back and changing your mind later.

 

[Noiz2]

There is no reason to go to the trouble of setting up a M/S setup if your going to decode it before recording. I'm not a fan of M/S but the only supposed advantage it has is the optio to take a clean mono (the M) and the ability to adjust the spread in post. You eliminate all of those by decoding before recording. And actually your heading is not very accurate since you don't seem to want to use M/S. It should be more like "need help recording stereo with a cardioid and a figure eight".

 

[DavidNJ]

Can't you use one relatively inexpensive ribbon mike (Nady's under $100, MXL for a little more, Oktava M-53 for $425) and an existing short condenser cardioid for M/S and two of the ribbons for Blumlein pairs?

 

[Steve House]

Can't you use one relatively inexpensive ribbon mike (Nady's under $100, MXL for a little more, Oktava M-53 for $425) and an existing short condenser cardioid for M/S and two of the ribbons for Blumlein pairs?

Sure, it would work from the physics POV but for best M/S results the two mics should be closely matched. I've been trying to get up the courage to order another Schoeps CMC amplifier to add to the one already in my kit, along with a MK4 and a MK8 capsule to go on them (already have a MK41). Plan B is a pair of Blueline's.

 

[carlosff17]

The cardioid equally to left and right I presume. Might work, but why bother?Why not do it the old-fashioned way ... record the cardioid on the left channel, the figure-8 on the right, and do the conversion/mix to stereo in post? I can't see any advantage at all of doing the way you suggest, there are too many areas where problems could occur and if you're only recorded the resulting mix, there'll be no going back and changing your mind later.

So...If i record by this way, directly for the recorder, you are saying that in post-production, i could use the "ms-decoder", to do this? to get the result as well as i could get by doing what i said before?

and, if i do by the way you said, i would record the "side" mic as a mono and the middle as mono too, as well...???

 

[Noiz2]

So...If i record by this way, directly for the recorder, you are saying that in post-production, i could use the "ms-decoder", to do this? to get the result as well as i could get by doing what i said before?

and, if i do by the way you said, i would record the "side" mic as a mono and the middle as mono too, as well...???

That IS what M/S is, two mono feeds. You "retrieve" the stereo in post by decoding it.

Why are you trying to record M/S if you don't even know what it is? I don't mean to sound judgmental but you really shouldn't be doing something if you don't understand it. There are a few reasons to to use M/S but it's not as simple to do as X/Y unless you have an M/S microphone. If you don't set it up correctly you can loose the benefits. And there is a catch and that is that there are very few benefits. The only real one is having a forward mono feed. That is useful in a few situations. I find the downsides far out weigh the minor benefits. But YMMV.

 

[DavidNJ]

Sure, it would work from the physics POV but for best M/S results the two mics should be closely matched. I've been trying to get up the courage to order another Schoeps CMC amplifier to add to the one already in my kit, along with a MK4 and a MK8 capsule to go on them (already have a MK41). Plan B is a pair of Blueline's.

If that is the case, you would have to use a small condenser, probably a small diaphragm condenser for both the the figure 8 and the cardioid. Is that correct?

 

[carlosff17]

That IS what M/S is, two mono feeds. You "retrieve" the stereo in post by decoding it.

Why are you trying to record M/S if you don't even know what it is? I don't mean to sound judgmental but you really shouldn't be doing something if you don't understand it. There are a few reasons to to use M/S but it's not as simple to do as X/Y unless you have an M/S microphone. If you don't set it up correctly you can loose the benefits. And there is a catch and that is that there are very few benefits. The only real one is having a forward mono feed. That is useful in a few situations. I find the downsides far out weigh the minor benefits. But YMMV.

Sorry for that, but i want to experiment! The sound will be perfectly captured by my shotgun mic, and with this ms-technique, i just want to experiment! sorry if i cause you so much trouble... by the way, do you know Frank Capra?

Do you know that he started to make cinema without knowing anything? well, that's just an example, but by your opinion, if you were there at that time, you should advised him that he souldn't started to make cinema...

People should experiment, and all i asked was some help with this technique...if i'm bothering you, just don't reply, ok?

 

[Steve House]

Sorry for that, but i want to experiment! The sound will be perfectly captured by my shotgun mic, and with this ms-technique, i just want to experiment! sorry if i cause you so much trouble... by the way, do you know Frank Capra?

Do you know that he started to make cinema without knowing anything? well, that's just an example, but by your opinion, if you were there at that time, you should advised him that he souldn't started to make cinema...

People should experiment, and all i asked was some help with this technique...if i'm bothering you, just don't reply, ok?

Of course, people start doing things not knowing anything but their first step is to study up and learn. Trial and error experimentation is fine but why repeat the trials and errors of those who have gone before when a few hours reading will let you start up at the point your predecessors left off.