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Old March 22nd, 2012, 11:32 PM   #1
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Recording for 5.1

Hi
I was told my someone (who for some reason couldn't explain to me why) that it takes two microphones to accurately reproduce the surround sound effect, and any production that requires this must record with two microphones.

I don't see many productions actually using two booms or lavs, especially for dialog. So basically my questions are:

1. Do we need two stereo microphones?
2. If yes, then does that mean using two mics on every dialog, sound effect, etc?
3. What is the basic post production workflow - which mic is used for L/R, and how does one decide that on set?

I'd appreciate any help, and if anyone can point to any other literature on the net, that'll be great, too. Thanks!
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Old March 23rd, 2012, 12:22 AM   #2
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Re: Recording for 5.1

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Originally Posted by Sareesh Sudhakaran View Post
1. Do we need two stereo microphones?
We will assume that you mean "two microphones for stereo". The overwhelming majority of sound for video/film production is recorded in monaural. Including virtually all dialog.

Quote:
2. If yes, then does that mean using two mics on every dialog, sound effect, etc?
Dialog: virtually never. Sound effects: maybe in some cases. But it isn't at all unusual to collect sound effects in monaural.

Quote:
3. What is the basic post production workflow - which mic is used for L/R, and how does one decide that on set?
There are a few popular stereo microphones that people use for collecting sounds. Reviewing the archives of this (and similar) online forums will reveal which ones. Certainly a stereo microphone does not qualify for the top 5 list of important equipment to have for recording decent production sound. You can make quite good production mixes without using any stereo microphones.

Waiting until you are on the set is rather too late to decide these kinds of things. Study some books and videos about production sound and learn how it is done before just assuming that you must have a stereo microphone.
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Old March 23rd, 2012, 07:04 AM   #3
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Re: Recording for 5.1

Thanks for replying. You're right, I actually meant two mono mics.

I've always used mono mics (own an ME66 still) and lavs for my feature and other production work. My feature was mixed in stereo, but the audio was just split 50:50; didn't have the budget for anything fancy.

But I did intend to mix in 5.1 and someone told me you can't mix in 5.1 with just a mono channel. That's what I hoped to find out - whether there is any truth to that statement. If, hypothetically speaking, one wanted a feature film mix for theatrical release, that is.
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Old March 23rd, 2012, 07:38 AM   #4
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Re: Recording for 5.1

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Originally Posted by Sareesh Sudhakaran View Post
Thanks for replying. You're right, I actually meant two mono mics.

I've always used mono mics (own an ME66 still) and lavs for my feature and other production work. My feature was mixed in stereo, but the audio was just split 50:50; didn't have the budget for anything fancy.

But I did intend to mix in 5.1 and someone told me you can't mix in 5.1 with just a mono channel. That's what I hoped to find out - whether there is any truth to that statement. If, hypothetically speaking, one wanted a feature film mix for theatrical release, that is.
Dialog is still done in mono, centred on the screen by panning equally into the left front and right front channels during mixing in post. So for dialog recording all you need is a single mono mic. Music is normally recorded in stereo. The "surround" part of the mix is created in post by panning normal stereo or mono tracks into the rears as desired. Likewise, the ",1" bass channel is split off in post, rarely if ever recorded in the field. While recording original ambience and FX tracks in 4 channel surround is not unheard of, it's still rarely done. (When recording an original track as true surround, it is recorded on 4 channels, not 6 - the 5th channel is the centred dialog, placed there in post, and the 6th ".1" track is the sub-bass, also created in post as mentioned above. Neither channel is actually originally recorded in the field into the channel where it ends up in the final mix, even if you are recording ambience or music in surround)
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Old March 23rd, 2012, 07:47 AM   #5
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Re: Recording for 5.1

You've got lots of info, but most of it is a little 'displaced' - correct for some things, but very wrong for another.

For conventional media products, dialogue is mono. Stereo is reserved for the music and effects. Practically all 5.1 sound is produced in the studio in post.

It's to do with context. Let's say shot one is of an evil looking priest saying a prayer in a cathedral, shot from a long way away to set the scene, you can see the aisles, the pews, the walls and probably the organ - it looks BIG. Next shot is a close up of him removing something from his pocket while saying the prayer out loud.

In shot 1, we hear the sound of his words from a distance, so quiet and reverberation quite evident - probably actually recorded close in, (let's ignore dialogue replacement for this example). So in post, his voice is thinned out, reverb added and then it's blended with the acoustic sound of a cathedral in stereo - plus the rear channels adding to the hugeness of the space.
In shot 2 - his voice is much closer - because the camera is right in there - yet the same huge space continues in the side and rear channels - the centre mono channel has a closer perspective to match the camera angle - but the other atmos tracks give the viewer the feeling of big space. Maybe the stereo front channels also have small effects - footsteps, maybe a little bit of hubbub from other people in the space, same at the back. Sort of immerses the viewer.

So if we assume the actual space was recorded, then we'd probably have a radio and/or a shotgun for the priests voice pickup and either spaced microphones or an X/Y pair for recording the ambience - perhaps with another set in the rear. This wild track would be edited to remove the odd shout or bang, and then the mixer would blend this all in to produce the surround sound. If you had a camera with so-called 5.1 sound it would NOT sound the same because real sound doesn't sound like what we 'think' it does.

The only time this doesn't apply is when the product is a live recording of an orchestral or choral work, and perhaps other sources that have a natural acoustic balance - folk bands with no electric instruments.

In this case a stereo recording is the main requirement. You have a choice of deciding to change audio perspective with the camera shots, or to leave it as it is. This is a common issue.

When recording an interview with three people, do you pan the middle one to the centre and the outer people left and right, to match their real position, or do you keep them mono and perhaps record the traffic passing in stereo? See the problem?

The Physics

To record stereo needs two mics. To record stereo with good imaging is much more difficult. Are you looking for effect, or realism? The test for realism is simple. listen with your eyes closed and point to the featured sound source. Open your eyes and see if it is where you are pointing. Most stereo recordings with pictures fail this test miserably. We are not really recording stereo, we're recording two channels - not at all the same.

You do see mobile stereo recording. It's quite common. A short shotgun like a 416 or similar, with a sideways facing fig-8 mic inside a zeppelin type windshield. You record in M/S - so mono for the centre and then the fig-8 mic provides the stereo side-to-side information. In post you can accurately control the width of the recording.

Turning all these sources into 5.1, complete with mono centre, stereo front, effects and sub bass is a complex process!

Planning for stereo is not a simple process. M/S 2 channel is probably the most useful technique for a single mic type shoot (even though there are really two!)
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Old March 23rd, 2012, 09:26 AM   #6
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Re: Recording for 5.1

The final film/video sound track is PRODUCED, it is not RECORDED. Even monaural finished sound tracks are mixed to produce the final product. It is never just the raw sound that was recorded. Even for fast-moving TV news they overlay voice-overs, and add wild-sound clips, etc.

And especially for stereo or higher output track counts, it is RARE that you go out into the location(s) and record 4-channel (never "5.1") The mix of sounds (including which channels they sound from) are produced artificially during the post-production mix-down. And very frequently using source clips that are monaural.

And the background sounds "ambience" are typically NOT recorded on the set, but somewhere that sounds like what is needed. That MAY be in the same place the dialog was recorded, but it is not unusual for the ambience sounds to come from somewhere else. Or even artificially created from various pieces like wind, traffic, birds, etc. etc.

The object of dialog recording is to EXCLUDE all extraneous sounds so that the editor has the maximum flexibility to combine foreground and background sounds to produce the desired final effect. So even if you want the ambient sounds from the set location, it is better to collect them before or after the actual video setup.
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Old March 23rd, 2012, 09:55 AM   #7
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Re: Recording for 5.1

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Originally Posted by Steve House View Post
... The "surround" part of the mix is created in post by panning normal stereo or mono tracks into the rears as desired. ... Neither channel is actually originally recorded in the field into the channel where it ends up in the final mix, even if you are recording ambience or music in surround)
Thanks for replying. I have a question: are there any significant advantages to be gained by recording the effects track and room ambiance in stereo?
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Old March 23rd, 2012, 10:01 AM   #8
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Re: Recording for 5.1

Recording effects in stereo can be a time-saving short-cut assuming the editor is skilled enough to use stereo clips properly. There are some things that are naturally stereo, like a passing train, etc. But it is also possible to create a convincing stereo passing train sound from a monaural source clip (by panning). And you could make the argument that it is easier to do it with a monaural source because then the location, speed, etc are fully under the control of the editor.
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Old March 23rd, 2012, 10:01 AM   #9
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Re: Recording for 5.1

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Originally Posted by Richard Crowley View Post
...
And especially for stereo or higher output track counts, it is RARE that you go out into the location(s) and record 4-channel (never "5.1") The mix of sounds (including which channels they sound from) are produced artificially during the post-production mix-down. And very frequently using source clips that are monaural...
Thanks. That's exactly what I was looking for. So theoretically assuming I've done a decent job of recording mono sound (full coverage), I can get a 5.1 mix done in post production without any worries. Would I be missing out on anything by going fully mono?

Also, that means the person who told me it was not professional to record mono sound for a 5.1 mix was incorrect, am I right?
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Old March 23rd, 2012, 10:19 AM   #10
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Re: Recording for 5.1

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Originally Posted by Paul R Johnson View Post
...
In shot 2 - his voice is much closer - because the camera is right in there - yet the same huge space continues in the side and rear channels - the centre mono channel has a closer perspective to match the camera angle - but the other atmos tracks give the viewer the feeling of big space. ...
Thanks for the great reply. In shot 2, does this mean raising the volume on the center channel or is there any other tweak involved?

Quote:
So if we assume the actual space was recorded, then we'd probably have a radio and/or a shotgun for the priests voice pickup and either spaced microphones or an X/Y pair for recording the ambience - perhaps with another set in the rear. This wild track would be edited to remove the odd shout or bang, and then the mixer would blend this all in to produce the surround sound.
A question: Isn't this the same as using many mono mics at the same time during the scene (assuming it was recorded during the take, but I know sound can be recorded at any time)? Is there an advantage in using stereo mics in this case?

Quote:
To record stereo needs two mics. To record stereo with good imaging is much more difficult. Are you looking for effect, or realism? ...We are not really recording stereo, we're recording two channels - not at all the same.

You do see mobile stereo recording. It's quite common. A short shotgun like a 416 or similar, with a sideways facing fig-8 mic inside a zeppelin type windshield. You record in M/S - so mono for the centre and then the fig-8 mic provides the stereo side-to-side information. In post you can accurately control the width of the recording.

Planning for stereo is not a simple process. M/S 2 channel is probably the most useful technique for a single mic type shoot (even though there are really two!)
I come from the school of thought that sound is as important as the image. So assuming we plan the sound design in advance, does this mean recording M/S throughout gives the editor/mixer the best possible raw material for a well-designed mix? I'm trying to wrap my head around the fact that the other answers suggest the 'normal' way is to record mono throughout, but is the process of recording M/S worth the trouble? Or is this something that is decided on a case-by-case basis?
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Old March 23rd, 2012, 10:33 AM   #11
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Re: Recording for 5.1

"I can get a 5.1 mix done in post production without any worries."
Even with pro mixer, there's worries. And you still have no control, once it's in the hands of the consumer... equipment, quality, placement, but that goes for mono or stereo too. 5.1 throws more factors into the equation.

"Would I be missing out on anything by going fully mono?"
If it's all dialog, mono is fine. Music tracks and some atmos' are nice in stereo, the dialog is still mixed mono... Panned to center, which comes out of both left and right speakers equally, which created a 'phantom center.'

"Also, that means the person who told me it was not professional to record mono sound for a 5.1 mix was incorrect, am I right"?
Right, this person does not know much about sound acquisition for picture.
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Old March 23rd, 2012, 09:41 PM   #12
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Re: Recording for 5.1

Thanks Rick! Could you tell me what the advantage is in recording effects in stereo? Does it help enhance the reality in post or is it just because it gives the mixer more options to play with?

The reason I ask is, it seems illogical to expect a stereo mic on set to capture the 'final space' of the edited film, and the effort seems like a compromise - for example, how different is it from capturing the same effect with two mono mics side by side?
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Old March 23rd, 2012, 10:20 PM   #13
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Re: Recording for 5.1

There are several Surround Sound mics produced or techniques...
I have used a borrowed Holophone on live to air broadcasting with stunning results.

SoundField: Benefits of a SoundField System
H3-D
Mitra 3D Mic Pro : 3D Mic Pro
Blumlein Pair - Wikipedia, the free encyclopedia
I have looked at the H2n | ZOOM and wonder what results it may deliver in the 360 deg mode for film production.
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Old March 24th, 2012, 06:01 AM   #14
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Re: Recording for 5.1

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Originally Posted by Brian P. Reynolds View Post
There are several Surround Sound mics produced or techniques...
I have used a borrowed Holophone on live to air broadcasting with stunning results.

SoundField: Benefits of a SoundField System
H3-D
Mitra 3D Mic Pro : 3D Mic Pro
Blumlein Pair - Wikipedia, the free encyclopedia
I have looked at the H2n | ZOOM and wonder what results it may deliver in the 360 deg mode for film production.
There's a huge difference in capturing sound for live-to-air broadcast and capturing various master tracks that are destined to be chopped up, blended, edited, and mixed to make the final soundtrack for a film. You don't go straight from camera to screen with the image and you don't do it with sound either. The finished product is created in post, not recorded on location.
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Old March 24th, 2012, 11:49 AM   #15
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Re: Recording for 5.1

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Originally Posted by Sareesh Sudhakaran View Post
The reason I ask is, it seems illogical to expect a stereo mic on set to capture the 'final space' of the edited film, and the effort seems like a compromise - for example, how different is it from capturing the same effect with two mono mics side by side?
-- What do you mean by "final space"? If your referring to 'Room tone'.. that is different, and normally recorded in the EXACT same configuration, immediately after, or during a dialog scene. Outdoor and other 'ambient' sounds are often recorded in stereo. Clothing rustle, door closings and other point source sounds are usually recorded and used in mono, but 'could' be panned off center in post, however that is not without potential pitfalls. If you have a good 'stereo' mic, there's no reason why one cannot record in stereo. An M/S mic would be a good choice for those types of S/FX.
Two mono mics placed side by side would likely have phase abnormalities (or worse) when summed to mono..
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