Topic: Acoustic Recording Techniques

[Thelonious]

Thanks gents, this is exactly the feedback I was looking for.

I have two follow up questions:
1) If I choose to go with three microphones (two adjacent NOS setup with slightly reduced angle and increased spacing, sharing a center) how important is microphone matching? As I don't have three identical mics the closest I could get would probably be the 461s for L/R with a 414 center (I'm assuming I would use the cardioid polar pattern for the 414).
2) Is there a single mic bar that you would recommend that would accomplish this or do I need to run my normal stereo bar with an additional mic stand for the center mic?

Thanks again!

[rocksuitcase]

Thanks gents, this is exactly the feedback I was looking for.

I have two follow up questions:
1) If I choose to go with three microphones (two adjacent NOS setup with slightly reduced angle and increased spacing, sharing a center) how important is microphone matching? As I don't have three identical mics the closest I could get would probably be the 461s for L/R with a 414 center (I'm assuming I would use the cardioid polar pattern for the 414).
2) Is there a single mic bar that you would recommend that would accomplish this or do I need to run my normal stereo bar with an additional mic stand for the center mic?

Thanks again!

2 ideas from me.
1] Manfrotto triple bar- is a bit heavy and probably too much ( money) for this one gig you describe   https://www.manfrotto.com/us-en/black-aluminum-triple-microphone-support-154b/
2] (NOT JUST a mic bar) but Smallrig rods and clamps- kindms bought and we use for most OMT we run.    https://www.smallrig.com/15mm-carbon-fiber-rod-30cm-12inch-2pcs-851.html   
                                                                                                                                                                       https://www.smallrig.com/list/Rod-Clamp.html
                                                                                                                                                                      https://www.smallrig.com/smallrig-single-railblock-860.html      (the mic mount)
smallrig is lightweight, modular, and awesome imo. kindms has 4 12" rods with connectors and we have enough mic mounts and pass through clamps to attach to a mic stand. 

[Thelonious]

Thank you for the ideas. The manfrotto bar on a mini tripod at the stage lip is a great option (whether2 or 3 mics). Thank you again for the ideas, they are very helpful!

[rocksuitcase]

Thank you for the ideas. The manfrotto bar on a mini tripod at the stage lip is a great option (whether2 or 3 mics). Thank you again for the ideas, they are very helpful!

welcome.  the triple bar
is LARGE and heavy.

[Gutbucket]

If I choose to go with three microphones (two adjacent NOS setup with slightly reduced angle and increased spacing, sharing a center) how important is microphone matching?  As I don't have three identical mics the closest I could get would probably be the 461s for L/R with a 414 center (I'm assuming I would use the cardioid polar pattern for the 414).

Not critical.  Decent matching is arguably a more important when recording in a more uniform soundfield.  On-stage and relatively close to the instruments you are sort of in a zone that lies between mic'ing the full ensemble with a single stereo array (where matching is somewhat more important) and individually spot mic'ing the three instruments (where it isn't).  Sort of a blend of both approaches, which is one reason I think it works well.

That said, always nice to use the same mics across the primary stereo array, as the identical response helps with consistency of image, smoothness across the soundstage, and the sense of depth.  I'll usually put the different mic in the center to maintain L/R symmetry, so any difference in timbre, which may be most apparent in the ambient/reverberant part of the recording, will manifest symmetrically across the center verses the sides, rather than one side verses the other.  Consistency of response/timbre is the general goal.  Polar pattern not so much. You can use a completely different polar pattern in the center without a problem.  In your situation where the L/R angle can be somewhat wide without problems it might help to use a somewhat wider polar pattern in the center than the sides, but should work fine using three cardioids.

In my OMT arrays I go back and forth between using identical mics across the L/C/R triplet to using a different pattern in the center.  I usually like using three identical mics, but have recently been switching to a more directional shotgun mic in the center when I want to nail a clear and distinct center from somewhat more of a distance.  Which is in a way, sort of the opposite of your on-stage situation. Horses for courses.

Years ago, I did a lot of on-stage acoustic jazz trio recordings over the course of a couple years, and settled on using three AKD TL's set to supercardioid pattern, placed as low as possible to the stage floor, arranged in a triangle with about a 90degree angle between the L/R pairs, angled up at the players positioned to either side of a central drum kit, with the center mic pointed up at the snare, just off center of the kick to avoid the direct "whump".  The supercardioid pattern helped with the narrow 90deg overall angle between L and R mics, and provided a bit more separation from the audience, which was being picked up by another dedicated pair facing out into the room.  The room/audience facing pair was very nice to have but not strictly necessary, but that three mic arrangement worked so well it became my go to for on-stage recording, and was later worked it into most of my recording arrays.  I like the three mic' stereo thing for taping.

[Thelonious]

This makes a lot of sense. I’m now thinking that the 3 mic PAS approach, with the c461a at 120 degree and 13 cm spacing with one 414 in supercardioid in the centre, allowing me to dial in the tuba a bit if required, may be a good starting point. Setting up about 12” off the stage floor and ensuring that the microphone on the right is off axis to the kick drum could be an excellent starting point.

I am always happy to record further back, in the sweet spot, for these types of shows but this approach seems to manage the crowd noise more effectively while providing an opportunity to balance the levels a bit if required.

Thanks again, this is extremely helpful.

[Thelonious]

[/quote]
welcome.  the triple bar
is LARGE and heavy.
[/quote]

Thanks again, I have ordered one and will plan for mounting it on something sturdy!

[rocksuitcase]

welcome.  the triple bar
is LARGE and heavy.
====================
Thanks again, I have ordered one and will plan for mounting it on something sturdy!

welcome to the triple bar club. I was speaking with Noah at Phish and looking at his bar mentioned I own one too, and he said, I own two!     

BTW Gut-  "did a lot of on-stage acoustic jazz trio recordings over the course of a couple years, and settled on using three AKD TL's set to supercardioid pattern, placed as low as possible to the stage floor"
I recall a nice thread with photos. Does that still exist to show thelonius?

[Billy Mumphrey]

Can you find a place where all the instruments sound well balanced?

I don't know how many similiar recording I've "ruined" by not following this advice. I would get so excited at the opportunity, I'd fail to realize certain instruments (usually the drums) would dominate a stage lip recording and not adjust accordingly. Yes, there was a wonderful upfront sound that you don't have with pure audience recordings, but with the mix of instruments being off (and usually unfixable), it's essentially unlistenable.

I think gut mentioned possibly setting up between the sax and tuba (further away from drums), and it's something to think about. Obviously the tuba is a great candidate to be low in the mix, and getting a supercardioid directly in front of and pointed at it (like you mentioned) could allow you to boost that mic in post and balance the mix. I apologize if I'm repeating anyone's advice, I'm slammed at work and haven't had time to read thoroughly but I wish you luck, sometimes you get these right and they're such wonderful recordings!

[Gutbucket]

BTW Gut-  "did a lot of on-stage acoustic jazz trio recordings over the course of a couple years, and settled on using three AKD TL's set to supercardioid pattern, placed as low as possible to the stage floor"
I recall a nice thread with photos. Does that still exist to show thelonius?

Yes! Was just coming back to post a link to the long-running on-stage taping tread where all that was going on, and it dovetails nicely with this one.  Voltronic, if you are reading, can you add a link to that thread along with your others at the start of this one?  Lots of good stuff in there.

Couple photos from that thread-




^
That second photo also includes another taper's rig on the slightly taller stand (AKG > Naiant little box > M10 and DVD battery visible on-stage), and an additional MG ORTF pair I was running for comparison in the Shure vert bar.  The LCR ADKs beat out the MG ORTF, but both were great.

[Thelonious]

Thank you for linking that stage recording thread. I’m working through it and it is indeed very relevant for acoustic recordings.

[voltronic]

I had recently posted on GS Remote wondering about the recommended Shuffling EQ settings for Alan Blumlein's close AB omnis:
https://gearspace.com/board/all-things-technical/1441717-blumlein-delta-shuffler-settings.html

As you will read, the thread got into a number of things, and today I posted samples of a concert I recorded last week where I used both the Blumlein close AB and the Gerzon/Faulkner 5 cm / 120 deg cardioid array, both which employ shuffling in post. You'll find those samples in this post, but I am also copying it below for convenience.

///

Ladies and Gentlemen, start your shufflers! As promised, here are samples done with Blumlein-style 22 cm AB omnis and Gerzon array cardioids.

This was my school district strings festival where the main purpose is for elementary, middle, and high school students to perform for each other. The younger students get to perform on the big stage, and to see/hear where they are headed in a few years, etc. We had a similar concert a few weeks before for our choirs.

The excerpts I am including are two pieces from a high school ensemble, and one each from two different middle school ensembles.

Mics were as you see in the photo. Preamps for the 4006 pair are Rens Heijnis modified; 4011 pair has stock preamps. Direct into my 788. There are almost a dozen different groups and only one stand location is possible, at the traditional behind the podium spot. I would have chosen different locations and heights for each of these arrays had I the freedom to do so. Mics were about 3 m high, and angled only very slightly down to aim above the heads of the last row of players in the largest group.

There are 3 versions of each excerpt for each array. DRY is self-explanatory, but still has a peak limiter on the master. Shuffle Only adds EQ according to the attached screenshots. MIX adds some reverb and compression but it is preliminary. All versions include RX Spectral Denoise to banish most of the HVAC noise.

I have a definite preference between the two setups, although there are some problems with each that cannot be shuffled away. I'll wait to share my opinions until others have listened.

https://samply.app/p/jcNlUgG3PFm7B8BGnxR6

I've found that Samply sometimes won't play at all in Firefox unless you manually disable Lossless in Audio Options, but it works fine in Chromium browsers. Either way, downloads are enabled for you to tinker with these. If Samply doesn't cooperate, here is a share that will be up for 7 days:
https://send.monks.tools/download/5edb36b17d1ba3bd/#EHZNI_MIKL9neFleIE1IIQ

EDIT: I made new versions of the 22 cm AB tracks, lowering the corner frequency and increasing the boost of the LF side channel shelf. As before, I rendered versions with only shuffling EQ and then "mix" versions with compression and reverb.
I didn't bother to do anything further with the Gerzon tracks, since they sound really awful for some reason I can't explain.
https://send.monks.tools/download/b3aca3bf3e95cbc0/#SVw6Pqvfc2Dnxq2g3vEkxA

[Gutbucket]

Thanks! Will take a listen..

To clarify for everyone, the "Shuffling EQ" Voltronic is talking about is a low frequency shelf boost applied to the stereo difference channel.  It is doing two things- increasing low frequency response and increasing the stereo difference content in the effected range.

The steps to do so are:
1) Convert the L/R stereo to Sum/Difference (Mid/Side)
2) Apply the low frequency EQ boost to the Difference (Side) channel
3) Convert back to L/R

That can all be done in one step with a parametric EQ set or operate in Sum/Difference mode.

If you wish to make a more honest assessment about what this is doing just in spatial terms alone without the low frequency EQ enhancement, you can apply a matching inverse EQ cut to the Sum (Mid) channel at the same time as the boost to the Difference (Side) [Edit- Easiest to just apply that inverse matching correction afterward to the L/R stereo output.  But if applying it to the Sum (Mid) you'll want to apply half as much gain to both curves, which together add up to the amount of gain originally applied to just the Difference channel alone].  In that case the overall stereo frequency response will remain about the same as was recorded with only the sum/difference ratio of the stereo content being effected.

For our purposes, the optimal choice of corner frequency, boost amount and whether to compensate the Sum (Mid) channel or not can be decided upon by ear, along with any additional EQ choices and any other post processing stuff (which might similarly be applied in L/R or M/S).  Whatever sounds best is right.

[Gutbucket]

More on "suffling"-

Alan Blumlein himself was an electrical engineer firmly rooted in mathematics, doing pioneering investigations into two channel stereo recording and playback at EMI back in the 1930s. His goal was a bit different than than ours as he sought to create a recording/playback system that would be as accurate as possible at that time.  He based his determination of specific corner frequency and amount of boost on the spacing he was using between the pair of microphones and the mathematical relationship between that distance and its relationship to acoustic wavelength. 

Most folks here will be familiar with Blumlein's pioneering use of a coincident fig-8 stereo microphone pair, which is the configuration with which his name is associated, but figure-8 mics weren't yet available to him early on, so his earliest experiments used a pair of omnis instead.

In order to produce a "stereo" output a pair of omnidirectional mics require spacing and/or baffling between them in order to produce a pathlength difference between the two. Blumlein separated two omnis by the approximate distance between a listener's ears and used baffle between them in order to derive useful stereo difference information.  The problem is that the amount of spacing required to produce useful stereo difference information varies with frequency. Head-spacing with a baffle produces effective stereo difference information starting at midrange frequencies and higher, where the sonic wavelength is "acoustically long" in comparison to the path length around the baffle from one microphone to the other.  But the wavelength of low frequencies is long in comparison to that short path length. The mic array becomes progressively more insensitive to stereo difference information at lower frequencies.

Blumlien compensated for that by boosting the stereo difference signal at low frequencies, and as a good engineer determined the parameters required to make that compensation based on the spacing/path-length between the two microphones.  I don't know if he states this outright anywhere, but we can infer that his intention was that the corner frequency of the EQ compensation made to the difference channel should be linked to the distance between the two microphones, tying it to the frequency/wavelength relationship as is made clear by the mathematics. He was making the best of a messy situation and simply accepted the complex phase relationships that were happening at higher frequency ranges. I imagine Blumlien was very happy when usable fig-8 mics became available to him and at that point was happy to leave baffled omnis behind.  Having the stereo pair of microphones produce stereo information while occupying a single point in space greatly simplifies the phase relationships and mathematics. 

Even though Blumlein quickly moved beyond using a near-spaced stereo pair of omnis at the time, and even though it took another couple decades for interest in stereo to really catch on, stereo shuffling remained and still remains a thing.  Provision for it was built into early "Stereosonic" stereo mixing consoles built in the UK where its use was somewhat ironically intended to enhance the stereo output of coincident stereo microphone pairs rather than spaced pairs.  The presumed future of stereo recording there at the time was based on addition of a Side channel microphone placed coincidently with the mono main microphone already in use.  There is a great paper on this from around the birth of commercial stereo in 1957 or so that I posted a link to at TS long ago.. I'll look for that to link here.

This is really no different than increasing the stereo width of a recording by altering its Sum/Difference (Mid/Side) ratio, except for being restricted to just the low frequencies.  We've discussed the details in various threads about Mid/Side processing here at TS, in which we've talked about making a low frequency EQ boost to the Side channel of an X/Y or M/S pair in order to make it sound more involving.  That's the application of "shuffling" same as in these examples.  And as used by Voltronic on these examples and as discussed in those threads, it can be applied to near-spaced microphone configurations as well as coincident ones.  The primary difference is that in non-coincident stereo mic'ing configurations it may be more important limit the enhancement to just the low frequencies where it is desired, where the phase difference between channels remains minimal.

Since our goal is more about creating an involving and good sounding recording than about accurate reproduction in its own right, we can play around with it and choose what to do or not by ear.  The low frequency boost this is providing is likely to sound good in its own right even if it isn't "accurate", since as mentioned above, "more accurate" would require a compensating cut to made to Sum (Mid) channel.  For example, the secret sauce in mixing my multichannel OMT recordings down to stereo is often the addition of some Center Side channel (otherwise not required because there are other L/R mic pairs providing stereo difference information) which often works out best with significant EQ applied to it - sort of bow-tie shaped curve - that serves to enhance stereo difference information at low and high frequencies while keeping everything tight and clean in the midrange.  If I want "more accurate" I mute it.  When I feel the recording is best served by a bit of enhancement that's honestly likely more "real-sounding" than actually real, I keep it in.

Have fun EQing your difference channel!

[morst]

For example, the secret sauce in mixing my multichannel OMT recordings down to stereo is often the addition of some Center Side channel (otherwise not required because there are other L/R mic pairs providing stereo difference information) which often works out best with significant EQ applied to it - sort of bow-tie shaped curve - that serves to enhance stereo difference information at low and high frequencies while keeping everything tight and clean in the midrange.  If I want "more accurate" I mute it.  When I feel the recording is best served by a bit of enhancement that's honestly likely more "real-sounding" than actually real, I keep it in.

Is the Bow Tie shape similar to the "Smiley Face" EQ that drunken sound mixers use to beef up excitement in the bass and treble range towards the end of a raging night at the rock club?

Really wanna mess up that center side channel? duplicate it and apply radically different eq to left and right... see image of what I imagine the Bow Tie to resemble?!?!?