Room Mic questions?

[AcousticDreams]

In regards to recording a single instrument in stereo, using two or more mics up close ( Auto Aligned ) &... a single room mic(NOT Auto Aligned with the others).

Question at hand:
* Is a single room mic far enough away (10 feet or more)= out of sync enough to not cause phase cancellation?
Or should the room mic be AutoAligned as well with the primary up close mics?

* That same question can also be asked about multiple mics spread out in one room recording multiple instruments. I hear some nice recordings with multiple players and mics in a mid size room. All the mics are hearing the other instruments. Should they also be Auto Aligned or are they far enough away to not cause problems?

Theories on my part ( which may or may not be correct. )
+ A room mic hears less dynamic volume range(the difference between higher volume and lower volume) than close up mics. A somewhat natural compressive sound of which the inverse square law dictates.
"as the distance from a source increases, the intensity is equal to a value multiplied by 1/d2"
In super simplistic terms, the dynamic volume range is smaller at a distance than it is up close.

+ A room mic hears the Reflected wall and Ceiling frequencies at nearly the same level as the primary instrument. The difference being the close up mics hear less of the reflected frequencies.

+ When we as the player play...we hear all of the above. We hear the guitar up close, and we hear the reflected wall frequencies & delays.

+ Our brain might even act as a volume control between the room sound and our close up sound. Adjusting the volume between the two.

+ The difference between adding a room mic and adding delay is: A delay just repeats the primary recording at a delayed time. A room mic hears the primary sound source and the reflections of the walls and ceiling on a more equal basis. However, the reflections are entirely different sounding than the primary source as the material that the sound is reflecting off of is reproduction a different frequency graph as well as a delayed time.

And finally:
* Should room mics be used in Omni? In cardiod? or do you use both patterns depending upon the room and distance?

[Bob Womack]

Room mics are typically used to pick up ambience. If you are going for that, you typically want to reject the direct signal as much as possible. Let me use a studio reverb chamber as an example. In those chambers you have a speaker, reflective surfaces, and one or two mics. Most often both the speaker and the mic face away from the center of the room and away from each other. There are also quite often "gobos," physical barriers, placed between source and mic that are used to reduce the direct sound. If there is any problem with leakage of the direct sound to the mics, the room is miked with directional mics to reject as much as possible. If you can get on the Abbey Road site and look into their reverb chambers via the virtual tour you can learn a lot.

Part of ambience is short-order delays. If you succeed in cutting the direct sound down to near-nil and then try to phase align the ambience, you'll actually be improperly aligning the sound, aligning the strongest delay to the miked source. You'll also loose the benefit of that delay. So, if the ambient is captured properly, no, you don't want to align the ambient. If you can use an omnidirectional mic without causing leakage or phase issues, that is preferred to prevent bass build up. However, it can be really hard to eliminate the direct sound, so the compromise is to face a cardioid or hemispherical pattern (PZM) mic away from the source. And remember, all of recording is a compromise so don't feel constrained to not use compromises.

Bob

[dnf777]

Originally Posted by Bob Womack

Room mics are typically used to pick up ambience. If you are going for that, you typically want to reject the direct signal as much as possible. Let me use a studio reverb chamber as an example. In those chambers you have a speaker, reflective surfaces, and one or two mics. Most often both the speaker and the mic face away from the center of the room and away from each other. There are also quite often "gobos," physical barriers, placed between source and mic that are used to reduce the direct sound. If there is any problem with leakage of the direct sound to the mics, the room is miked with directional mics to reject as much as possible. If you can get on the Abbey Road site and look into their reverb chambers via the virtual tour you can learn a lot.

Part of ambience is short-order delays. If you succeed in cutting the direct sound down to near-nil and then try to phase align the ambience, you'll actually be improperly aligning the sound, aligning the strongest delay to the miked source. You'll also loose the benefit of that delay. So, if the ambient is captured properly, no, you don't want to align the ambient. If you can use an omnidirectional mic without causing leakage or phase issues, that is preferred to prevent bass build up. However, it can be really hard to eliminate the direct sound, so the compromise is to face a cardioid or hemispherical pattern (PZM) mic away from the source. And remember, all of recording is a compromise so don't feel constrained to not use compromises.

Bob

Bad news: I only understood about 10% of that explanation.

Good news: that makes me 10% smarter than when I woke up today!

I was just thinking of posting the question of how many home recordists add in an “ambiance” room mic track. Ive seen this highly recommended on more than a few YT vids, and with the ease of MTR, was going to play with the idea. Maybe even some outdoor ambiance of birds, woodpeckers, or whatever nature provides.

[ChuckS]

Originally Posted by Bob Womack

Room mics are typically used to pick up ambience. If you are going for that, you typically want to reject the direct signal as much as possible. Let me use a studio reverb chamber as an example. In those chambers you have a speaker, reflective surfaces, and one or two mics. Most often both the speaker and the mic face away from the center of the room and away from each other. There are also quite often "gobos," physical barriers, placed between source and mic that are used to reduce the direct sound. If there is any problem with leakage of the direct sound to the mics, the room is miked with directional mics to reject as much as possible. If you can get on the Abbey Road site and look into their reverb chambers via the virtual tour you can learn a lot.

Part of ambience is short-order delays. If you succeed in cutting the direct sound down to near-nil and then try to phase align the ambience, you'll actually be improperly aligning the sound, aligning the strongest delay to the miked source. You'll also loose the benefit of that delay. So, if the ambient is captured properly, no, you don't want to align the ambient. If you can use an omnidirectional mic without causing leakage or phase issues, that is preferred to prevent bass build up. However, it can be really hard to eliminate the direct sound, so the compromise is to face a cardioid or hemispherical pattern (PZM) mic away from the source. And remember, all of recording is a compromise so don't feel constrained to not use compromises.

Bob

I haven't been doing much home recording of guitar lately, but for my field recordings (choirs, small ensembles) I have to deal with capturing some ambience. Since my field recordings of concerts have an audience it's not been practical to place omnis deep in the hall/church. In order to minimize direct sound getting into my fairly close ambient mics what I've been doing is using a pair of near-coincident cardioids pointing upwards and away from the choir (the choir is in the null of the mic array). In some cases I have the ambient pair located behind the choir and pointing away from the choir & audience, and in some cases I have the ambient pair located in front of the choir and pointing upward and toward the audience.

[Mobilemike]

A (very general) rule of thumb, is that to avoid phase issues between microphones, your far mic should be three times farther away from the source than your near microphone. So if your main microphone was 1 foot away from the guitar, you could place an ambience mic 3 feet away (or farther) and not have to stress about phase. Generally, ambience mics do not get phase aligned with the main mics.

Multiple mics on different instruments may or may not need phase alignment. There will always be bleed between those microphones, and part of a recording engineer’s job is placing those mics where the bleed is beneficial to the overall sound, not harmful. You will have to use your ears on this one - if you hear anomalies when summing multiple mics, then phase alignment might help.

[AcousticDreams]

Originally Posted by Bob Womack

Room mics are typically used to pick up ambience. If you are going for that, you typically want to reject the direct signal as much as possible.
Bob

This is quite different than I ever expected. When you say you should reject the direct signal as much as possible...this would be in the Mix?

If so, is there a percentage ratio you recommend between room mic(ambient) and the direct mics?

I would have guessed previously( with no knowledge) that the room mic would be 30 to 40% and the stereo close mics would have been around 60 to 70% of the mix.

But you are saying reverse of that, and even more? What percentage should the Stereo close mics be?

[Bob Womack]

Originally Posted by AcousticDreams

This is quite different than I ever expected. When you say you should reject the direct signal as much as possible...this would be in the Mix?

If so, is there a percentage ratio you recommend between room mic(ambient) and the direct mics?

I would have guessed previously( with no knowledge) that the room mic would be 30 to 40% and the stereo close mics would have been around 60 to 70% of the mix.

But you are saying reverse of that, and even more? What percentage should the Stereo close mics be?

Microphony and mnixing are both artistic endeavors. If we are talking about studio recording, the close mics are typically the foundation of the recording on an acoustic guitar. The room mics are used to prevent the guitar from sounding too dry. The blend between the two depends upon how dry the room is and how wet you want your mix to be.

However, I've seen pictures of Chet Atkins with multiple pairs of mics at approximately one foot, two feet, four feet, and six feet. That was in a recording studio. I'd bet they had multiples up at the beginning of a session trying to figure out how to get a good sound rather than using all of those.

Bob

[KevWind]

Originally Posted by AcousticDreams

+ The difference between adding a room mic and adding delay is: A delay just repeats the primary recording at a delayed time. A room mic hears the primary sound source and the reflections of the walls and ceiling on a more equal basis. However, the reflections are entirely different sounding than the primary source as the material that the sound is reflecting off of is reproduction a different frequency graph as well as a delayed time.

First I don't use a room mic so can't really give an informed comment on that

But as for above. I have a few thoughts

So to back up a bit obviously the main difference is that a room mic is a source and delay is an effect One recorded in and the other mixing effect.
I would think you are correct that the a room mic (depending on the room ) is going to reproduce some of the ambience of room refections So my question would be ,, would using a room mic be more like a reverb effect ?? (which is also different than a delay)

Interestingly I have now taken to using both a Tape delay and a reverb on my vocals both in parallel , as well as two compressors (one direct one parallel) .

So in this video I have I have the UA LA2A plug in (optical) comp directly on the vocal track and the track outputs to my 2 Bus with my Hardware (VariMu type) comp then I am also sending the vocal to both a Tape Echo delay and my Hardware Reverb
Also the Rif guitar has the same Tape Echo delay (with more delay,) on it as well and the main Rhythm guitar is sending to the Hardware reverb also
he backup vocals are dry

[Doug Young]

Originally Posted by Bob Womack

However, I've seen pictures of Chet Atkins with multiple pairs of mics at approximately one foot, two feet, four feet, and six feet. That was in a recording studio. I'd bet they had multiples up at the beginning of a session trying to figure out how to get a good sound rather than using all of those.

There was this crazy photo of Will Ackerman's mic setup a while back. I've got to wonder how many of these were actually used, or even live. Maybe some are just sitting out in case someone wants to use them...



There was another I came across years ago that I can't find anything with Tony McManus in a studio with mics all over the place, even some placed way behind him.

[AcousticDreams]

Originally Posted by Bob Womack

Room mics are typically used to pick up ambience. If you are going for that, you typically want to reject the direct signal as much as possible. There are also quite often "gobos," physical barriers, placed between source and mic that are used to reduce the direct sound.

If you can use an omnidirectional mic without causing leakage or phase issues, that is preferred to prevent bass build up. However, it can be really hard to eliminate the direct sound, so the compromise is to face a cardioid or hemispherical pattern (PZM) mic away from the source. And remember, all of recording is a compromise so don't feel constrained to not use compromises.
Bob

O.K I get it now( thanks to Doug who explained to me what you were actually saying) I totally mis understood what you were saying. Super great info.

In my particular case, this is actually possible, as I have gobo's out in front of me...as well as Wall panels behind me. Enough to help reduce the direct sound. And great info about facing cardiod away. I would have not thought about that either.

In my case of recording Stereo Acoustic guitar using two close up direct mics on acoustic guitar.)
? Would you use ONE room mic..or Two room mics? One room mic would offer a solidarity of reflections and let the close up mics give you the solid stereo image. Two...might confuse the stereo field competing with the close up stereo mics? As the room mic is only being used for Ambience. What do you think?

[Bob Womack]

If you have good separation between the direct sound and the ambience you can go with a pair of mics in any accepted coherent stereo array to prevent phase problems. I am partial to the ORTF near coincident pair array because it is phase coherent and offers a wider field than X/Y coincident pairs but there are many more patterns such as measured spaced pairs.

Bob

[DupleMeter]

Originally Posted by AcousticDreams

In regards to recording a single instrument in stereo, using two or more mics up close ( Auto Aligned ) &... a single room mic(NOT Auto Aligned with the others).

Question at hand:
* Is a single room mic far enough away (10 feet or more)= out of sync enough to not cause phase cancellation?
Or should the room mic be AutoAligned as well with the primary up close mics?

* That same question can also be asked about multiple mics spread out in one room recording multiple instruments. I hear some nice recordings with multiple players and mics in a mid size room. All the mics are hearing the other instruments. Should they also be Auto Aligned or are they far enough away to not cause problems?

If you have to resort to AutoAlign, you're not setting the mics up properly. Don't fix phase issues after the fact, check mics (test record even) and adjust until there are no obvious issues (swapping the polarity on one channel (left or right in a stereo playback) can help highlight issues.

Phase issue happen when a single source is picked up by 2 mics at varying distances at the same intensity/level (or near enough to the same level). Playing with distances between mic arrays & the source is how you find a good setup that s free from phase issues.

Originally Posted by AcousticDreams

Theories on my part ( which may or may not be correct. )
+ A room mic hears less dynamic volume range(the difference between higher volume and lower volume) than close up mics. A somewhat natural compressive sound of which the inverse square law dictates.
"as the distance from a source increases, the intensity is equal to a value multiplied by 1/d2"
In super simplistic terms, the dynamic volume range is smaller at a distance than it is up close.

Well, the dynamic range is similar, only at a level that is representative of the change in distance. So you are not getting compression you are simply getting the natural reduction of wave energy from distance. The change of that wave energy from the player is the same, only reduced for distance.

Originally Posted by AcousticDreams

+ A room mic hears the Reflected wall and Ceiling frequencies at nearly the same level as the primary instrument. The difference being the close up mics hear less of the reflected frequencies.

Only if your room is too small for a room mic. Those are not desirable things. Most room mics are setup with several feet to any boundaries (walls/ceilings). I would recommend against using a room mic in a home setup, unless you have a large house with a great room that allows for significant distance from all boundaries.

Now, that doesn't mean you can't pull back on your main mic array.

Originally Posted by AcousticDreams

+ When we as the player play...we hear all of the above. We hear the guitar up close, and we hear the reflected wall frequencies & delays.

+ Our brain might even act as a volume control between the room sound and our close up sound. Adjusting the volume between the two.

Again, I NEVER want to hear reflected sound from walls/ceilings. They tend to sound horrible. A room mic is used to get a distant pickup for the tonality that distance brings & how it alters the perception of the source. Things become more cohesive from a distance. You hear less microscopically and more as a whole.

Originally Posted by AcousticDreams

+ The difference between adding a room mic and adding delay is: A delay just repeats the primary recording at a delayed time. A room mic hears the primary sound source and the reflections of the walls and ceiling on a more equal basis. However, the reflections are entirely different sounding than the primary source as the material that the sound is reflecting off of is reproduction a different frequency graph as well as a delayed time.

And finally:
* Should room mics be used in Omni? In cardiod? or do you use both patterns depending upon the room and distance?

For me, I add a room mic to add depth & size to a source - though, with more & more mixes going Atmos, I'm finding room mics are great for the rear surrounds. Adding a sense of being surrounded by the sound.

Simply delaying a sound is very different. It's going to sound like a repeat or slapback, but not a real room. The changes the distance makes to the sound won't be present. Again...I never want reflections form walls.ceilings, they sound harsh & cause comb filtering.

And for room mics I often use ribbons, so I'm stuck with figure-of-8 as my pattern. Either stereo or mono. If it's stereo then it's Blumlein (XY pair of figure-of-8s).

[mixsit]

Originally Posted by Mobilemike

A (very general) rule of thumb, is that to avoid phase issues between microphones, your far mic should be three times farther away from the source than your near microphone. So if your main microphone was 1 foot away from the guitar, you could place an ambience mic 3 feet away (or farther) and not have to stress about phase. Generally, ambience mics do not get phase aligned with the main mics.
[clip]..

There's a couple of points to counter here. First being the '3-1 distancing doesn't provide improvements or corrections in phase.
Essentially the only 'in phase point is equal distance, i.e.; equal arrival times at the mics.
The placement method's distancing and purpose is to provide attenuation of unwanted phase issues (differences.
But then we might want to have the 'far mic up in the mix..?
So.. there goes the attenuation too.

[j3ffr0]

I don't bother about ambient mics in my studio. Without treatment, my room wouldn't be any good at al, so it's heavily treated. Although many of my treatments our range limited, it'd still more dead than not. There's not much to pickup other than chair squeaks, breathing, stomach growls, and farts.

Ambience is reverb plugins for me.... although I do have a large bathroom with decent reverb. I might try something in there at some point just for fun.