Topic: Basic checklist for my first recording?

[Gutbucket]

All true, although I'd modify that slightly

Generally, omnis are good when the room/concert hall sounds good and when the sound is not hindered by other problems like HVAC/People coughing/etc.

 
And simply leave it at that for this situation.

As mentioned, a lot of things are interrelated and simple answers are hard to summarize.  With a few exceptions like nearby rattling vents, HVAC noise is usually mostly indirect, reverberant noise rather than direct arriving sound. Because of that, switching to directional mics won't make as much difference as adjusting microphone position to increase the level of the sound you want compared to the noise you don't want.  Cardioids usually don't have the same flat response to the lowest frequencies as omnis so even though the HVAC noise is diffuse, it's mostly very low frequency noise and a cardioid with less bass sensitivity will pick up less of that low frequency information, but also pick up less low frequency musical information from the performance and low frequency room envelopment as well.  If the problem is an HVAC airstream blowing directly across the mics, cardioids will have more of a problem than omnis since they are more suseptible to wind rumble. 

People will cough.  With non-amplified music such as this with quiet segments you will hear it regardless of microphone pattern. This boils down to personal preference, situation, and sometimes a case of the ailment being preferable to a less than totally effective remedy.  I prefer to accept coughs as part of a natural sounding enveloping room ambience rather than compromising the recording to get a somewhat quieter, but less natural sounding muffled and mono-reverberant coughs.  Your microphone position high and closer to the band than the audience will help greatly with this.  If you were recording a PA amplified band with a rowdy crowd, you could more effectively reduce the crowd noise by using directional microphones, which would likely also be a good choice for other reasons.

If you want the absolute best recording you can make and have the time, inclination and resources to edit it and learn some specialized tools, you can use software to nearly erase isolated anomalies like coughs and squeeks from quiet recordings, without compromising the positive aspects of the recording by choosing a less than optimal microphone configuration in an attempt to reduce the problem.  But that’s advanced stuff.

[RemotelyLocated]

Many thanks again and yes I'll check out the Williams article when I have a moment. My biggest concerns with this venue are: 1) mic stand placement and 2) HVAC roar. Audiences should never really be a problem.

As shown in my photo, they'll let me put a stand on the floor at stage lip. I don't recall any practical room for a stand on the stage but maybe I'm wrong about that, or maybe I was wanting dead-center and the band director's platform comes right to the stage lip.

That said, if I'm to try spaced omnis (and I am agreeable to trying it) then it would seem I need to get a second mic stand --- I don't see me getting a bar wide enough, because I won't be back far enough? Regardless, I'd be inclined to introduce another variable and lower the stand(s) somewhat ... get them closer to the band and further from the HVAC above, as well we be less visually intrusive.

[Gutbucket]

If you have a second stand and it's cool to put both up, that will make rigging things and adjusting the spacing easier.  In that case I'd start with a 2' or 3' omni spacing and wouldn't go wider than 4' to start for the setup you posted the photo link to.  Even 4' might be pushing things there.  Wider still can work, but without a third mic in the center (which would allow you to double those spacings), much wider than that could be problematic.  If mounted on a single stand with some sort of mounting bar, you probably won't be able to go that wide, but you might manage 15" to 2' or so, which might be just right, even 12" might be enough.  For a chorus you can space them more widely if you want without problems.

Either way, from looking at your photo, I'd probably keep the stand(s) high with the mics pointed downwards towards the center of the group, but not try to move them any closer.  It's already close enough for both practical stage-space and sonic reasons, arguably even slightly too close for cardioids.  If the band was farther back on the stage and there was more room behind the conductor you could go lower, even down to stage level itself which sounds crazy but can work well, although it risks musicians stepping on the microphones and places the mics closer to the front rows of the audience making crowd sounds more audible.  Very low is least visually intrusive and very high can be less visually intrusive than mid-high as long as you route the cables cleanly so only the thin black stands block anyone's view.

When you read the Stereo Zoom, don't worry too much about corellating it to the omni spacing distances I've mentioned here.  It's the relationship between spacing, angle and pattern for directional mics which is the important thing to grasp there.

Before changing things too much to try and reduce the HVAC noise, if you have the opportunity at a rehersal or something the next time you are there, stand near the microphones, close your eyes, try to force yourself to forget where you are, then listen to discern if the HVAC noise is audibly localizable as coming from directly above or not.. or if that's simply where your eyes and brain tell you it is coming from. 

[RemotelyLocated]

They don't rehearse in the auditorium and setting everything up to test isn't an option. I'd get maybe 1 minute of band tuneup to adjust levels before hitting Record.

Hard for my mind to grasp how spaced mics aimed straight ahead (even omnis) less than 4', and when so close to the stage filed with players spread wide, wouldn't still emphasize the players right near the middle. I think that's one reason why I used ORTF/cards last time. Am I wrong here?

Regarding the HVAC noise, I noticed that during setup when there last Spring ... it comes from directly overhead the stage. I hope they fired the architect or whomever designed that system. It was loud and on quiet passages easily competed with the music. That worries me with omnis, still. Out in the audience there's no HVAC noise over them. It's as if the room's only HVAC output comes from the stage? Nice auditorium nonetheless and not the gymnasium many high schools must use.

That said, I'd rather have to shelve down some from about 150Hz-down in post, as I had to do with much of my initial recording, than alter mic placement or choice in an attempt to not pick it up here: I'm convinced it's unavoidable unless I can get them to turn it off.

Gutbucket you've given me a lot of good info and I appreciate it!

[2manyrocks]

I have a choir situation where the HVAC vent is overhead (stage right) and a very large return vent is behind the stage on the right, too.

So I positioned a mesh pop filter between the mic and the vent.  It helped, but I'm open to other suggestions.  I don't have any solution for the return vent noise. 

[Gutbucket]

Hard for my mind to grasp how spaced mics aimed straight ahead (even omnis) less than 4', and when so close to the stage filed with players spread wide, wouldn't still emphasize the players right near the middle. I think that's one reason why I used ORTF/cards last time.

Although more can be better, 3’ is plenty and is something of an A-B baseline starting point for me for 2-channel stereo.  I’ll walk you through the mechanics of why it works-

Usually we want to fully fill the playback space between the speakers with the sound sources on stage, so that the musicians on the far left and right are reproduced from the left and right speakers and the musicians located between them are spread out evenly between the speakers.

Even though there are some signal level differences, A-B stereo is primarily based on the difference in arrival time of the same sound at each microphone. A timing difference of around ~1 millisecond is enough to pan a sound fully to one speaker or the other.  In one millisecond, sound travels about 1 foot.  With the microphones 1’ apart, we get that full 1ms timing difference only for a sounds arriving directly from one side of the other.  Sounds arriving from any other angle will have a path length difference of less than 1 foot and a smaller time of arrival difference, which means all of those sounds will be reproduced somewhere between the two speakers.  That means a one foot spacing produces a Stereo Recording Angle of 180 degrees. (approximately)

Stereo Recording Angle is a Stereo Zoom term which describes an imaginary window looking forward from the microphone perspective, framing the region which will be reproduced between the two speakers. All sounds arriving from within that window will be heard as coming from somewhere between the speakers and all sounds from outside that window will be fully panned over to one speaker or the other.  So with an SRA of 180degrees, a musician fully to the left side of the microphones is heard from the left speaker and the one fully to the right from the right speaker. Those between them will be heard as coming from somewhere between the two speakers.

A perhaps unintuitive aspect of the Stereo Zoom is that the farther apart the microphones are, the narrower the SRA becomes.  As the distance between microphones is increased, the 1ms timing threshold is reached at arrival angles closer to the centerline, outside that angle the timing difference will be greater than 1ms. 

If the microphone position is moved farther away from the source, we typically want to compensate with a narrower SRA, so that the band will still fully fill the playback stage between the speakers.  That requires a larger spacing between the mics.  So usually, the farther away an omni pair is located from the source, the wider apart you want to space them.  That’s the zoom part of the Stereo Zoom.

With the mic stand position you have in that hall, the band is arrayed in almost a full half-circle around the microphones, which is why a 12” spacing that gets something like a super wide 180 degree SRA wouldn’t be unreasonable.

If the micophones are spaced too widely, on playback the sound will either come from the middle or will be clumped at one speaker or the other and not evenly distributed between them.  People talk about a ‘hole in the middle’ on playback with over-wide mic spacings, but the sounds actually arriving from the middle (through the narrow SRA) will still sound centered, its just that there is less sound evenly distributed between the middle and the sides. You’ll just get a clump at the left speaker, a clump in the center, and a clump at the right without an even distribution between them.

Understanding that, I still like more spacing than the Stereo Zoom suggests for omnis because there are other things going on with this too.

[Gutbucket]

More on the Stereo Zoom-

Directional microphones complicate the simple timing-based SRA relationship by also introducing signal level differences between channels.  The level differences are due to the angle between microphones and the shape of their polar sensitivity pattern.  Less spacing is required compared to A-B since those level differences pitch in to do some of the work.   The opposite extreme from timing based A-B stereo configurations are coincident X/Y patterns, where the mics are co-located in the same point in space and there are no timing differences. All the work is done by level differences.  Near-spaced configurations split the work between both timing and level differences, and you choose that balance by adjusting mic patterns, angles and spacings.  The Stereo Zoom is a way of understanding and manipulating that balance to our advantage.

[RemotelyLocated]

the farther apart the microphones are, the narrower the SRA becomes.

Yeah and you use that when further back to capture the timing differences better.

I think I see why, because of what you said earlier, "All sounds arriving from within that window will be heard as coming from somewhere between the speakers and all sounds from outside that window will be fully panned over to one speaker or the other."

Narrowly spaced mics seem at first to me like they'd miss capturing the extreme sides (especially with close stage-lip placement) but in fact "work" because any source extremely L or R, while down in level compared to smack dab in front, instead gets "highlighted" in the mix as just what it is in playback, extremely L or R in the presentation.

Is that sorta correct?

***********

3’ is plenty and is something of an A-B baseline starting point for me for 2-channel stereo.


Even so close to the stage, or because I'd be so close to the stage?

Overall I think I get it ... I recall reading elsewhere 4' is a common minimum for A-B but that likely assumes mic placement further back which is why 2-3' feet apart is likely plenty here.

[Gutbucket]

Narrowly spaced mics seem at first to me like they'd miss capturing the extreme sides (especially with close stage-lip placement) but in fact "work" because any source extremely L or R, while down in level compared to smack dab in front, instead gets "highlighted" in the mix as just what it is in playback, extremely L or R in the presentation.

Is that sorta correct?

Yeah, it might help to think of it in terms of this simplification-
In terms of left/right imaging with an A-B setup, consider the sounds arriving from anywhere on the stage to be of about the same level regardless of where they come from.  Think of the level differences that do exist (along with the timbre differences and differences in the amount of direct sound compared to reverberant sound due to some things being farther away) as affecting the apparent 'depth' in the recording more than the left/right imaging.

"3' is plenty and is something of an A-B baseline starting point for me for 2-channel stereo."

Even so close to the stage, or because I'd be so close to the stage?

I’ve found that a good practical starting point for me both up close and from farther away.  You’ve hit on something though, and that’s when up close, things get more complicated because there begins to be more level differences possible for some specific sources simply from greatly increased proximity to one mic or the other and other things going on.  Maybe that suggests that far away means a bigger spacing, closer means less spacing, and when very close you can go either way for different reasons.  So for other things like instrumental jazz and rock bands, I might put omnis across the stage lip and space them at 3 or 4’ intervals.  That’s more than the time-of-arrival difference theory alone suggests and the increased level differences would seem to amplify that even more so, but it works well and I like the sound I get from it.. and that’s what’s most important. All this technical stuff just helps to figure out how to get the sound I want.  Sometimes it applies clearly and sometimes it doesn’t.

A somewhat standard way of professionally mic’ing orchestras is to have a main pair of omnis above and behind the conductors head that are only about 2’ apart and produce most of the left/right stereo imaging based on the SRA stuff, mixed with another much wider spaced pair flanking them which provide the width and spaciousness sound of wide spaced omnis, along with some section balancing.  The idea is to sort of combine the best of both approaches.  Several of the classical halls I visit use that setup in a permanent hanging arrangement.  I do something similar, but use three mics with just one in the middle and less spacing out to the wide mics.  In that case my starting point is ~3’ between each, for about ~6’ overall between the left and right microphones.

[Gutbucket]

I have a choir situation where the HVAC vent is overhead (stage right) and a very large return vent is behind the stage on the right, too.

So I positioned a mesh pop filter between the mic and the vent.  It helped, but I'm open to other suggestions.  I don't have any solution for the return vent noise.

A pop filter isn't going to do much since it's purpose is to let as much sound as possible through while blocking air-blasts.  You would be better off doing the same thing with something blocks sound like a baffle.  A Jecklin disk repurposed for the job might work if you have one.

Come to think of it, a Jecklin disk may be a good option for you to use both omnis on one stand, RemotelyLocated.  If you're not familiar with it, its a flat baffle with sound absorbing material on it which is placed between to near-spaced omnis to make them somewhat directional, providing increased side to side level differences at mid and high frequencies.  It makes the omnis act more like cardioids and allows you to use a standard narrow mic-bar and place them much closer together than would otherwise work.  It blocks sightlines, but it is oriented edge-on to the audience and with your stand that high it may be above anyone' line of sight.  In my experience, they work very well up close where they produce very natural sounding recordings that are less-bright sounding with more anchored imaging but less low end envelopment than wider A-B spaced omnis. Many around here have made their own disks and there are threads about doing so.  They seem to pop up again every few years.

[2manyrocks]

My vent situation is a bit unusual in that this particular supply vent blasts a stream of air to the point that you can feel the air moving past the mic.   Positioning the pop filter between the mic and the air source cut out the air roar. 

In a situation where the air is diffuse, then a pop filter wouldn't be helpful.  The noise in that instance is the noise of the air moving through the vent instead of air moving past the microphone. 

In Remotely Located's situation, it would be nice if he could hang his mics so there's no mic stand for any harpist's moms to complain about.   

[RemotelyLocated]

My initial recording that started off this thread was about recording the band's concerts. I'd also been trying to get hold of the choir director; he's got a concert coming up next week. I finally did and here's his reply:

"... personally I would love to have you come and record the group.  However, earlier this semester all of the music teachers in the county were required to attend a copyright clinic and per county policy we are putting a statement in our program saying videoing and recording is illegal.  In order to legally do that, we would have to purchase the rights of each individual song on the program.  Whereas I wish this option was available for my kids, I'm not going to risk any legal issues. 
Thanks"

I think he's equating parents recording with the school doing a recording for themselves (which would essentially be my role here) but can't see arguing the point if it's a misinterpretation. Still, I feel I should respond in some way, at least ask if "the clinic" made such a distinction. Also, I might not have been clear enough in my intention to record.

[RemotelyLocated]

OK I got a little fired up about this. Here's my reply to the choir director, and I cc'd the band leader.

"Dear ___,

I understand and share your concern and priority. However, copyright law actually does permit you (the educator) to record and have one copy of a student performance, and this has been true since 1976.

Unless I'm mistaken the clinic wanted to make it clear that anyone else couldn't possess a copy and that's why parents aren't allowed to record and why we can't give them a copy I make.

Worth a read, particularly the "Recording" paragraph:
http://musiced.nafme.org/resources/copyright-center/copyright-law-what-music-teachers-need-to-know/

To be clear, any role I play would strictly be on behalf of the school, without any intention of distribution and would be happy to enter into a simple contract that says so. I enjoy the practice and the experience of recording as a hobby but that's as far as it goes --- I don't even have my kids at EHS yet.

If the District's policy makes a blanket statement that doesn't address the educator's right to one recording of a student's performance, consider raising (an obvious) red flag for yourself and your colleagues.

Regards, ...."

[Gutbucket]

My vent situation is a bit unusual in that this particular supply vent blasts a stream of air to the point that you can feel the air moving past the mic.   Positioning the pop filter between the mic and the air source cut out the air roar. 

In a situation where the air is diffuse, then a pop filter wouldn't be helpful.  The noise in that instance is the noise of the air moving through the vent instead of air moving past the microphone. 

In Remotely Located's situation, it would be nice if he could hang his mics so there's no mic stand for any harpist's moms to complain about.   

Okay, in that case the pop filter is acting more like a windscreen and may be more appropriate than a baffle.  A baffle may help block vent noise/rattle coming from a specific direction if you can place it between the mic and the source of noise.  Low frequency HVAC rumble is diffuse, essentially coming from all directions in the room, and a small baffle wouldn’t be large enough to block those low frequencies it even if it was coming from a specific location, so there isn’t much you can do about that by way of setup other than getting the microphones relatively close to the source to improve the signal to noise ratio.

Hanging mics make sightline problems easier, but are much, much more hassle to setup and orient unless you can make a permanent rig that you simply lower and attach the mics to. They are also a lot more difficult to adjust if you want to play around with different mic setups.   


Can’t help with the copywrite stuff.  Isn't there is an exception for educational use?
[Ignore that, just saw you latest post]

[RemotelyLocated]

Got a reply from the other director. Seems that yes, they had the bejeezes scared out of them via a PowerPoint slideshow--no documentation, nothing from the school District itself--by a representative (the person who gave the "clinic") Soundzabound..which is a royalty free music site. Still a mystery as how this became District Policy.

<sigh>

I have the guy's name and email now but might instead just go to the District Superintendent.