Topic: Acoustic Recording Techniques

[Gutbucket]

^ Must be a mistype.  For the two to equate the metric measurement would be in cm not mm.

2.1 / d where d is the capsule spacing in inches
5.4 / d where d is the capsule spacing in mm cm

Now thinking about what that's based upon..

Here are a few data points:
22 cm spacing equates to a frequency of 245Hz using the formula above.
245hz equates to a wavelength of 140cm.
140cm / 22cm = 6.36.. cm

I'm assuming it's based on the phase coherence/correlation associated with that spacing, which for any spaced pair is high at low frequencies and low at high frequencies, connected by a curve that shifts downward in frequency as the spacing is increased.  Below is the coherency curve for a pair of omnis AB spaced 22cm apart as indicated by the Schoeps Image Assistant.  Looks to me that 245Hz is the approximate center point of the curve. 

[Edit to update the screenshot of the coherency curve to include the scale on the right side of the graph, consistent with the screenshots in the following post]

[Gutbucket]

From my perceptual point of view..

In spacing the omni mic pair in my multichannel setups - where the omnis can be spaced relatively widely without incurring a "hole in the middle problem" because there are additional directional microphone channels placed in the centered between the omnis - I find I most prefer the omnis spaced around 2 meters apart, and that's what I usually do.. because that's about the maximum by setup can support from a single stand. More spacing can work nicely but doesn't seem to be necessary and is more difficult to arrange because it requires additional stands or clamp positions along a horizontal railing to support them.

Looking at the coherency curve for a pair of omnis spaced 2m apart in Image Assistant, the approximate center point of the curve lies around 40Hz.  Ok, that makes sense to me perceptually.  With a 2m spacing no shuffling is needed to achieve a nice very low DFC (diffuse field correlation) all the way down to a sufficiently low frequency.

Now, the spacing I generally recommend in my posts here at TS for a pair of omnis used in typical taper situations is about 1m.  The qualities I listen for from a spaced omni pair suffer rapidly as the spacing is made narrower than that, at least without the application of shuffling.  More up to 2m is better but more difficult to setup for most tapers.  So 1m ends up being the practical recommendation.

Looking at the coherency curve for a pair of omnis spaced 1m apart in Image Assistant, the approximate center point of the curve lies around 80Hz.  Which also makes sense to me perceptually.  Low enough to  to achieve a sufficiently low DFC even though in perceptual terms it could be improved on with a bit more spacing.

However, it seems to me that most tapers have a hard time achieving a 1m spacing unless using miniature omnis.  Most are using narrower spacingings, so let's assume half that.  A 50cm omni spacing will place the center of the curve at about 160Hz, so most of the low bass information will have relatively high DFC. 

The tentative conclusion is that shuffling may perceptually improve any recording made with an omni spacing of around 1m or smaller, and the corner frequency of the shuffling filter can be set lower the wider the spacing.  The corner frequency may be determined by using the formula above or might just be set it by ear.

Here are screen shots of the coherency curves for 2m, 1m and 50cm:

[voltronic]

Thanks for catching my typo, and for reminding me about Schoeps IMA which is such a handy tool. Your conclusions about the DFC seem very logical.

[Gutbucket]

Thanks for starting the conversation on shuffling with your examples.  Super interesting stuff.  Hope I haven't gone too deep into this for the others following.

A few of my conclusions-

• I'm now convinced that a not overly wide spacing in combination with shuffling is an optimal arrangement for a stereo pair of omnis when used on their own.. in most cases - there are always exceptions and I think those tend to arise in taper situations more so than typical recording scenarios. The oddity of superwide 20-30 foot omnis splits sometimes working great for PA amplified stuff without suffering a "hole in the middle" is an example of that.
• This is great news for tapers!  Less wide spacings are far, far, far more practical, achievable, and less-imposing.
• Application of shuffling may make for an improvement of any taper recordings made with a coincident or near-spaced pair.  That's most of them.
• Thinking about how it might apply or not to multi-microphone arrays, meaning those which include a microphone, pair, or more mics placed in the center between a wider spaced pair. Forgive one additional indulgence in thought experiment about that before I let this go..  actually, strike that.  Probably best if I take that over to the OMT thread.

[voltronic]

Gut, you should check out this thread on GS. Heva gets amazing results recording pipe organs using just a Sennheiser Amebo headset and iPhone. Some discussion of shuffling / widening begins in post #5.

https://gearspace.com/board/remote-possibilities-in-recording-amp-production/1364259-binaural-pipeorgan.html

[Gutbucket]

Thanks, will do.

[Thelonious]

Hello folks, I hope everyone is doing well! I have the opportunity to record a "big band" next week in a very small club and I was hoping to ask a couple of questions. Please see the pictures below for the layout on stage. Although everything is mic'd (at least to some extent) the volume of direct acoustic sound from the horns is pretty substantial relative to the PA and this dynamic is new to me.

First a bit of context. The band includes a keyboard, guitar, bass, drums and ~8 horns. At least some instruments are fed directly to the board (guitar is going through a helix straight to FOH) so I need to be back far enough to have some PA in the mix but don't want to lose the organic sound coming from the stage. The room is tiny for a band this size (25' across?) but quite deep. Last week I sat second table back from the stage dead centre and the sound was good and very loud. I am thinking no more than 3' back from there as towards the back of the bar there is another room and I don't want any chatting to compete with the music.

I am thinking of using cardioids (184s?) in somewhere between DIN and NOS, depending on the stereo angle I have from the point I want to mount the mics. My plan is to run into a zoom F3. There is a lip that runs along the ceiling (like the frame between 2 rooms in a house) about 10' back from the stage and I believe one option is to clamp from somewhere on that lip and to have the mics hang down. The other option would be to clamp to a table and have the mics raised above the head height of the patrons, who will be seated.

My questions are:
1) If I hang mics from the ceiling, how far do they need to be to not be negatively affected by the reflections?
2) Do cardioids make sense in this case? I prefer the bass response of more open mics, and could use open cardioids instead, but I am a little worried about reflections.
3) Is there anything else I should be thinking about that I may not have considered?

The good news is that the band is loud enough (where I was last week, just forward of where I may mount the mics) that I am going to bring proper hearing protection so I'm not particularly worried about crowd noise if I need to mount to the table. It would not be reasonably possible to talk over the music at that volume.

Thank you in advance for any advice on this. As always it is greatly appreciated.

[rocksuitcase]

1] I would say 2 feet below is fine. I've had to run them closer, but the room makes the call for you usually on this variable.
2] With all those horns and a loud PA, Cards may be a wise choice. Compared with omnis that would tend to reduce the bass or low frequency room reflections.
3] horns are LOUD. Try not to be on axis with the trombone or trumpets. 

[Gutbucket]

The table from which those photos were taken looks ideal to me, assuming there is sufficient PA coverage at that position to get sufficient guitar and keys. I'd use the open cardioids from there.  The slightly more open pattern is likely to work well with a big band, should help the horns sound a bit more rounded out and less "strident", and make for a bit softer more blended stereo image.  Looks close enough to avoid problems of too much room or sidewall reflections. 

If hanging the mics, make sure they remain within the good radiation pattern of the PA speakers.  Keeping them low enough that they are not above the vertical cutoff of the high-frequency horn would likely be my main concern, other than the general challenge of hanging mics and routing cables in support of that.  Clamping to a table will be a lot easier, yet blocks view from behind more.

Try to recall from the previous performance how the trumpet players in particular tend to point their horns.  If they tend to angle them upward toward the ceiling over the audience's heads during the loudest stabs and passages, maybe best not to hang the mics from the ceiling if that will place them directly on-axis for the loudest blares.

Whatever the height, in regard to vertical angle I'd point the pair so as to be in-line with the drums.  I awleays like to get a clear and direct line of sight to the snare if I can.

[Billy Mumphrey]

yep lots of good advice above. fortunately, i believe cards or wide cards would sound good, but my instinct says to go with wide cards if people talking (during the actual music) isn't an issue. the only issue with cards is the extra directionality(?) could result in too much PA or too much onstage horns if you get the angle/mic position slightly off (which I have personally done, multiple times, in similar situations). wide cards would be a little more forgiving imo and (usually) sound great when working with actual onstage sound.

I always love clamping from the ceiling as it's less clutter/interference on the floor. around 2 ft from the ceiling, as advised by rock, is similiar to my own findings. gut is also correct that the PA speakers should determine the vertical positioning. getting them as close to the center of the PA would be ideal IMO.

All of my trumpet/ trombone encounters have generally pointed their horns downward, but I have seen video of some that play upward. I also like to point the mics to drums like gut. but like rock, I have recorded things similar to this and the horns were very loud and kind of dominated the recording. because of this my instinct says to angle mics SLIGHTLY towards PA (instead of stage) but I COULD DEFINITELY BE WRONG and I highly encourage you to use your knowledge of the band and room to make the final call. Better yet, if you're able to be there for soundcheck, you could get a better sense of how to angle the mics. If the soundguy is blasting non-horns through the PA, then a 50/50 blend of onstage and PA is a safe bet.

These kinds of recordings are so fun to me. I think being in the actual room, walking around and gaining a 3D perspective of where everything is helps a bunch.

[Thelonious]

Thank you all very much, this exactly the feedback I needed. The trumpets play facing ever so slightly down towards the mic when soloing (see pic) and the Pa speakers are mounted quite high at more or less at the same height (pic 2). Based on your responses my plan A will be to mount open cards about 2’ below the main ceiling (slightly less below the part than hangs down to which I will be clamped) and ensure that I am below the high frequency section of the PA speakers. The open cards should be more forging of sound arriving off axis (most of the horns in the centre of the stage) and hopefully that off axis will help with the fact that the trumpet is roughly in line with the mics vertically. I can angle them down from there to be aimed (vertically) closer to the drums.

There isn’t much of a sound check as these folks are pros and they roll in within half an hour of start time and there are just a few level checks of individual instruments before the show and then they start. Luckily, I was there last month and was able to scope out the situation. The sheer volume of the horns had me intimidated. I think the key will be getting there very early to mount to the ceiling and route the cables etc as I’m concerned mounting to the table, while much easier, would be too visually obtrusive.

Again, I really appreciate the feedback. The leader of this band has a lot of interesting projects in town and if I produce a good recording this could lead to a lot of opportunities for interesting recordings in the future.

[Thelonious]

Thanks for the advice on this show. It really turned out very well (probably my best recording?) so thanks again. I have permission to share samples so I have put a song up if anyone is interested (no pressure at all). I welcome any feedback.

https://we.tl/t-5UNlC4KiRt

Link is good for 7 days...

While there were mics for all instruments, there was significant direct sound from both the drums and horns and I can, at times, here the imaging of both the actual horn and PA location.

mk22/cmc6 (modified ORTF) ~6.5' high, ~6' back from front of stage, 2' LOC>Zoom F3 (96/24)
SD>Audacity (levels only, no EQ)

[Billy Mumphrey]

Just listened to the sample track, sounds great man. I've seen many many comments here professing love for the mk22 capsule, and this recording just confirms it. Sooo natural and even sounding, but NOT flat at all. It's lively, but not unnaturally hyped. I think I'm a Schoeps guy even though I don't own any (yet).

Anyone else hear that little bit of imaging when the first horn licks start off the song? Very cool. That's what acoustic recording is all about.

Also the small amount of crowd reaction starting around the 2:45 mark, that's what audience recording is all about.

I particularly love the quieter sax solo's (both musically and recording-wise) starting around 4:30. In the louder parts the horns tend to be stronger BUT I don't think that's your fault, it is a Big Band after all and I guarantee you if you asked any of the horn players they'd probably want to be turned up even more

[Thelonious]

Just listened to the sample track, sounds great man. I've seen many many comments here professing love for the mk22 capsule, and this recording just confirms it. Sooo natural and even sounding, but NOT flat at all. It's lively, but not unnaturally hyped. I think I'm a Schoeps guy even though I don't own any (yet).

and...

I particularly love the quieter sax solo's (both musically and recording-wise) starting around 4:30. In the louder parts the horns tend to be stronger BUT I don't think that's your fault, it is a Big Band after all and I guarantee you if you asked any of the horn players they'd probably want to be turned up even more

Thanks for the kind words Bill.

I am extremely happy with the mk22 for all the reasons you mentioned. I recorded 4 shows previously with them and was equally delighted, however, I used a modified NOS for those as the music was all being amplified and the SRA required to capture the PA was very narrow.

I would say that the advice to use wide cardioid for this application was very helpful. When I got into position, I needed a 110' angle to capture the PA sounds, which meant that the trumpets were almost dead in front of the mic or 55' off axis of the capsule. The MK22s did a really good job capturing the acoustic signal that far off axis. I suspect CM4s would have performed well in this instance as well.

I think the increase in loudness between the trumpets and the saxophones was due to the acoustics involved. The bell of the trumpet was pointed almost directly at the mic position and, as a result, was providing a lot of energy even ~12' away. My ears are still ringing.  I assume that is why they are positioned in the back row and the saxophones, which radiate sound from the keys as well as the bell which is facing upward, are up front.

Another approach might have been to move 10' back but that was not possible as there was no fixture from which to mount the mics and would also have resulted in much more noise from the back room relative to the music. I was very happy with the audience to music mix at this distance.

[Gutbucket]

Thanks for the advice on this show. It really turned out very well (probably my best recording?) so thanks again. I have permission to share samples so I have put a song up if anyone is interested (no pressure at all). I welcome any feedback.

https://we.tl/t-5UNlC4KiRt

Link is good for 7 days...

^
Just came back to hear this but missed the x-fer window, may I beg a re-up?