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Author Topic: Stereo Technique with MK41 or other super-cardioid Microphones  (Read 1926 times)

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Offline DSatz

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Re: Stereo Technique with MK41 or other super-cardioid Microphones
« Reply #15 on: June 27, 2018, 02:18:16 PM »
just want to point out that heathen's reply is correct; for Ambisonic decoding to work, the GAIN of each recording channel must be exactly the same. Normally no effort should be made to make the levels equal; it's the gains that count. In any real-world recording the peak levels will almost certainly differ among the four channels, and that is as it should be.
  • Gain is the degree of amplification that occurs between point A and point B in a circuit or system. It can be "unity" a/k/a 0 dB, or it can be some positive number of dB or it can be negative, in which case the minus sign is usually dropped and then the number that remains is the amount of loss.
  • To calibrate the gains of the four channels precisely, if you can record some rehearsal material, make a rough setting so that all four controls are as similar as you can get them "by eye" and the highest individual level obtained via the microphone doesn't quite reach 0 dB. Note which channel had the highest peak levels. Then don't touch that one channel's record level control; we're going to adjust the other three channels to match its gain. Disconnect the microphone, and connect a signal generator to that channel, set the generator to some midrange frequency, and adjust its output level (not the recorder's level) so that the meter on that channel reads exactly 1 dB below full scale (assuming that your meters have a nice, clear marking for that exact level; if not, choose the exact level with the clearest marking available). Then attach the generator to each of the other three channels in turn--or if you can split the signal, do that; either way, don't adjust the generator's level, but instead set the record levels in the other three channels all to exactly the same level as you set the first channel to.
  • If you don't have any rehearsal or "throwaway" material, just set the levels the best you can, but conservatively enough that you definitely won't need to change them during the recording. At the end of the recording, again without touching the recording levels, use a tone generator to record a midrange reference tone on each channel (or on all four at once if you can split it). The level can be anything that's convenient below 0 dB. Then when you go to decode the recording, adjust the decoder's input level controls to make those four recorded reference tones all have equal levels.
--best regards
« Last Edit: September 19, 2018, 03:29:07 PM by DSatz »
music > microphones > a recorder of some sort

Offline relefunt

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Re: Stereo Technique with MK41 or other super-cardioid Microphones
« Reply #16 on: September 18, 2018, 11:36:53 PM »
This is my favorite thread I’ve read on TS so far. It gives me something to think about each time I read it (about half a dozen times so far).

A sincere “thank you” to everyone who has contributed to it!
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Offline wlp

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Re: Stereo Technique with MK41 or other super-cardioid Microphones
« Reply #17 on: September 19, 2018, 07:50:54 PM »
- All that said, there's an interesting variant on omnis that can produce surprisingly good results sometimes, and that is to embed the membranes of each microphone in the surface of a sphere (see attached photo). I wonder whether you've tried this technique with your omnis. (Add-on sphere accessories are available for various microphone diameters.) It's another one of those adaptations or compromises that I spoke of, but this one completely preserves the spaciousness and "envelopment" aspects of spaced-omni recording, while increasing the clarity and directness of the direct sound sources.

Can anyone point me to where these add-on spheres can be found.  I'd like to try these for a pair of Senn 8020 mics.

Offline if_then_else

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Re: Stereo Technique with MK41 or other super-cardioid Microphones
« Reply #18 on: September 19, 2018, 11:38:39 PM »
https://www.shapeways.com/product/VVM7XHA2G/acoustic-sphere-19mm-mic-40mm-diameter?optionId=61442338

Not sure though, if they will fit tightly with the mkh-8020s as their grille is irregular shaped. (I've got some 8020s myself.)

Offline DSatz

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Re: Stereo Technique with MK41 or other super-cardioid Microphones
« Reply #19 on: September 20, 2018, 06:27:16 PM »
... also, they're shown as fitting on Schoeps mikes which are 20 mm diameter, not 19.
music > microphones > a recorder of some sort

Offline wlp

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Re: Stereo Technique with MK41 or other super-cardioid Microphones
« Reply #20 on: September 20, 2018, 08:08:32 PM »
Apparently, they are offered multiple sizes.  I'm going to try a pair and will report back on the results.

Offline aaronji

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Re: Stereo Technique with MK41 or other super-cardioid Microphones
« Reply #21 on: September 21, 2018, 10:03:20 AM »
^ DPA also offers these, the Acoustic Pressure Equalizers, in three diameters.  The DPA mics are 19 mm, so I would imagine these would also fit other 19 mm mics.

I seem to recall Gutbucket also has a home-brewed solution using some type (Nerf?) of hard foam balls...

Offline if_then_else

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Re: Stereo Technique with MK41 or other super-cardioid Microphones
« Reply #22 on: September 21, 2018, 11:03:55 AM »
^ DPA also offers these, the Acoustic Pressure Equalizers, in three diameters.  The DPA mics are 19 mm, so I would imagine these would also fit other 19 mm mics.

I seem to recall Gutbucket also has a home-brewed solution using some type (Nerf?) of hard foam balls...

If it's for both the d:dicate 4003 and d:dicate 4006A, its inner diameter might be only 16mm.

Online Gutbucket

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Re: Stereo Technique with MK41 or other super-cardioid Microphones
« Reply #23 on: September 21, 2018, 11:16:47 AM »
Mine are appropriate for the miniature 4060 (5.4 mm dia) omnis I made and use them for, but I'd suggest either whichever Neumann/Schoeps/DPA spheres fit the Senns, or Shapeways 3D printed spheres made specifically to fit them.  The 3D printed stuff was not an option when I worked up the DIY Nerf hard-foam ball spheres or I would have explored that route. 

With the 3D printed option, I'd keep an eye/ear out for resonance of the plastic and any empty internal space within the sphere.  If that seems suspect, you might want to fill any internal void with something.
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Offline beenjammin

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Re: Stereo Technique with MK41 or other super-cardioid Microphones
« Reply #24 on: September 21, 2018, 08:13:56 PM »
This has been such a good thread, and I hope that it may continue to be of service to those looking for info on stereo configurations with the MK41 and other super/hyper cardioid mikes.

A quick update to my original post: I think I've settled on a Jecklin disk with my MK2s. This gives me the stereo separation I initially sought. As far as reach, I took a cue from photographers with wide angle lens and focus with my feet, placing the mikes closer to the source.

In fact, I've been running the Jecklin disk handheld! While I have to be very careful, I've found that if I'm quiet enough I can get very good results. This has an added benefit. Instead of setting the mikes on a stand and letting them run for hours, I now capture what I want and edit on the go. If some sound interferes with the recording, I end the take and move on. I've never had so much fun recording.

There are two drawbacks. One, the Jecklin disk gets heavy, and after about 12 minutes, my arm needs a break. Hopefully, I'll build up more muscle mass. Two, I look like a madman. People notice me running around and seem to have no clue what the hell I'm doing. I figure it's only a matter of time till someone calls the authorities.

This summer I was up on Mt. Hood in Oregon, trying to capture Bumble Bees and a pair of wildflower hikers thought I was tracking mountain lions!  :guitarist: 

Offline achalsey

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Re: Stereo Technique with MK41 or other super-cardioid Microphones
« Reply #25 on: September 22, 2018, 12:51:38 AM »
^ DIY J-Disk, or purchased?  I'm not sure how you're holding the disk, but a monopod would definitely be your friend.  I don't know anything about them, but I do trust the internet.  Maybe someone else can chime in on that front.

https://www.adorama.com/alc/best-monopods-for-cameras

Offline beenjammin

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Re: Stereo Technique with MK41 or other super-cardioid Microphones
« Reply #26 on: September 22, 2018, 10:31:35 AM »
I picked up the Josephson disk and run it with a hand grip. It was expensive (~300) but much cheaper than a new set of caps. I have a light stand with me at all times, but monopad is a very good idea. One nice thing about running everything handled is the ability to move through thick brush with (relative) ease.

Incidentally, it appears that the Jecklin disk requires a slight hi frequency lift to compensate for the acoustic baffle. I guess one of the MK2 variants -- h, s, x -- would be ideal, but I read a thread on Gearslutz where someone claimed to have it on authority of a Schoeps engineer that the right in-software filtering could render any two variants acoustically identical. I've been playing around with a simple high shelf filter with good results.

In any case, this summer's recording has made me a Jecklin convert. Save the lovely Schoeps KFM omni sphere, I can't think of anything better for my purposes.

Here's a link to an example made by someone in the UK of the KFM sphere:

https://aporee.org/maps/?loc=14813&m=satellite

Offline DSatz

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Re: Stereo Technique with MK41 or other super-cardioid Microphones
« Reply #27 on: Yesterday at 09:33:34 AM »
beenjammin, it's not primarily the Jecklin disk itself that calls for a mild high frequency lift in the microphone's free-field response; it's the miking distance.

Practical, professional-quality omnidirectional microphones aren't omnidirectional at high frequencies because of their physical size. And omnidirectional microphones at normal, audience-type miking distances pick up only a relatively small proportion of direct sound as compared with reflected sound. Before reaching a microphone that's not pretty close to the direct sound sources, reflected sound has almost always undergone absorption that affects the high frequencies more than low or mid frequencies.

Thus if you choose a capsule like the Schoeps MK 2 for recording at a distance in a reverberant space, you will get a dark sound; its super-flat on-axis curve (how flat can a curve be, and still be called a curve?) doesn't apply when the predominant sound energy is coming from off-axis.

I've attached several graphs to this message. One shows the approximate difference between the on-axis response of a small (Schoeps-sized) omni and the general, integrated response of the same capsule to sound arriving from random directions in three-dimensional space (a/k/a the "diffuse-field" response). Omnidirectional microphones have more of this difference than any other type except shotgun microphones. (Conclusion: Shotgun microphones designed for placement fairly close to the direct sound source aren't a good bet for more distant recording in reverberant environments.) (Oh--that's every shotgun microphone ever made by anyone.) (Oops.)

But yeah, in most Jecklin arrangements, the capsules don't face the direct sound sources. So that's a factor, too.

> I guess one of the MK2 variants -- h, s, x -- would be ideal, but I read a thread on Gearslutz where someone claimed to have it on authority of a Schoeps engineer that the right in-software filtering could render any two variants acoustically identical.

The MK 2 S would be my suggestion. And yes, all four of Schoeps' omni capsules have essentially identical polar response (see attached graphs) and all other parameters, except their free-field (anechoic, on-axis) response. Thus if you equalize them appropriately, they become interchangeable with one another both on- and off-axis. That's not "inside information" nor is it a situation unique to Schoeps.

(note that in the attached graphs, the old MK 3 is still called by that name; it was renamed to "MK 2 XS" a few years ago, but it's the same capsule. It has approximately flat response when placed in a diffuse sound field, i.e. where rather little of the incoming sound is direct/on-axis. This makes it a special-purpose item in terms of modern, stereophonic recording, but it still has some applications today.)
« Last Edit: Yesterday at 03:23:29 PM by DSatz »
music > microphones > a recorder of some sort

Online Gutbucket

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Incidentally, it appears that the Jecklin disk requires a slight hi frequency lift to compensate for the acoustic baffle.

beenjammin, it's not primarily the Jecklin disk itself that calls for a mild high frequency lift in the microphone's free-field response; it's the miking distance.

True that miking distance is the primary factor by far, and I certainly do not mean to contradict DSatz, yet from personal experience I've found there is truth to the statement about Jecklin disk recordings benefiting from more high frequency lift than a recording made without the baffle using the same omnis from the same recording location.  I know other tapers have reached the same conclusion.

I'm not certain exactly why that seems to be the case, but I suspect it might have to do with one of two things, perhaps both in combination-
1) Compared to the direct arriving sound, the reverberant pickup using a Jecklin disk is somewhat darker than when not using the disk.  The directionality imparted by the disk off-axis is not constant with frequency.  The baffle is not absorbing/blocking any sound at the lowest frequencies, yet does so increasingly as frequency increases, and because of that, the reverberant pickup becomes darker in comparison to the direct sound.  This makes the overall balance of the recording (both direct and reverberant combined) somewhat darker without any EQ compensation applied.
2) The presence of the baffle reduces phase interaction between the two channels at mid and high frequencies, and perhaps the comb-filtering phasiness without a baffle attenuating it translates as brighter sounding. 

Would very much like to hear your thoughts on this David.  I hear this frequency balance effect clearly, but perhaps I'm attributing it to the wrong things.
« Last Edit: Today at 12:18:08 PM by Gutbucket »
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

 

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