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Author Topic: Cardioids which are most natural sounding off-axis? On-axis sound secondary.  (Read 10715 times)

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Offline Gutbucket

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I'm sure that all sound ridiculously over-complex, but it really works very nicely.  Except for attaching the Gefells to the XLRs, it's pre-rigged and not at all complicated to setup.  I tend to test these more complex variations a few times, and then make a better informed decision on what is and what isn't important and refine things from there.

The omnis in both cases are miniature DPA 4061.  I can easily see an appropriate pair of miniature low-voltage cardioids or subcardioids working perfectly fine as rear facing microphones in both the heavier/high-quality and lighter/more-economical rigs.  So I suppose the next practical question is which miniature low voltage directional microphones sound natural enough well off-axis, recognizing that they are unlikely to be as well behaved as the high quality microphones metioned earlier in the thread are the effective ideal?

If a subcard pair has enough low end response, they could possibly take the place of 4061, reducing the channel count to 5, or keeping it at 6 if the center rear cardioid is retained.
« Last Edit: July 30, 2014, 04:23:30 PM by Gutbucket »
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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Gutbucket

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So here's a few thoughts which were bouncing around in my head when I started the thread, and which I now realize is what I really wanted to discuss most (even though I asked for specific microphone suggestions, and thanks for those)- 

What is the ideal off-axis response in comparison to the on-axis response?  Might it differ by application and perhaps by polar pattern as well?  Is an omni with an off-axis response which is identical to the on-axis response a measurement ideal or an musically appropriate ideal?  Is an off-axis response that is identical to the on-axis response in all aspects except for a difference in signal level that is constant with frequency musically ideal for a directional microphone?  These are clearly quantifiable and challenging engineering ideals, approached by some of the top quality directional microphones mentioned in this thread.  Stereo recording setups are often devised based on simplified modeling of microphones with this type of idealized behavior, as are the visualization programs which are commonly linked to around here. 

I’m intentionally asking these questions rhetorically.  I know (or believe I know) some of the reasoning behind all this, but I’m intentionally questioning both my own experience as well as common practice in trying to better assess what the appropriate ideal response might be for various applications. 

Here’s two specific examples, the first common, the second more of what I’m trying to get at with this-

All but the very smallest omnis with capsule and housing diameters become increasingly directional at high audible-range frequencies can be used to advantage rather than simply being considered an inevitable engineering tradeoff of capsule diameter.  Musical feature or bug?

It strikes me that some 180-degree off axis cardioid responses appear very similar in shape to human perceptual equal loudness curves.  If accurate enough and smooth enough, might that kind of response be advantageous if leveraged in such a way that sounds arriving from off-axis become loudness curve filtered as their level drops compared to the on-axis response?   I'm imagining a 90 degree off-axis cardioid response which emulates the -6dB down human hearing loudness curve from whatever the designer chooses as a nominal on-axis response level, with increased curve filtering for sounds arriving from farther to the rear producing signal levels lower than -6dB and less so for sounds arriving from angles more on-axis with levels higher than -6dB, morphing smoothly to whatever the target on-axis response is: free-field flat, a far-field diffuse curve, or whatever.

Is the answer 'perhaps so for some applications but it's too complicated to engineer that kind of behavior correctly'?
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<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

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Offline Len Moskowitz (Core Sound)

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So I'm wondering if there may be cardioids with excellent off-axis response, which may not be a first choice on-axis wise.  Odd request I realize, partly just thinking about the implications here.

This was mentioned, and I see that you considered it: TetraMic or any other well-calibrated ambisonic microphone can be decoded to give you an excellent solution. What you're calling "off-axis response" can be as good as you want it to be. What makes it probably the world's finest Blumlein can make it one of the finest cardioids with excellent off-axis response.

And for what it's worth, even though their native patterns are never used, the capsules in TetraMic are sub-cardioids.

If you want non-coincident patterns, you can use more than one.

I see that you also want to avoid recording four channels and having to decode. Please keep in touch with us - we're working on some really good stuff.
« Last Edit: August 03, 2014, 04:48:05 PM by Len Moskowitz (Core Sound) »
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Offline Gutbucket

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Len, I have thought a lot about this while playing around with virtual microphone patterns from the Tetramic.  It has the potential to be an excellent tool for exploring these questions given the appropriate decoding tools. This is one area in particular where the virtual pattern synthesis capabilities of an ambisonic microphone system like the Tetramic makes possible things we cannot otherwise achieve or test easily.

Can you point me to any B-format tools which can do the following?

1) Specify a changing polar response which varies between any two first order patterns, smoothly by frequency.
2) Specify a changing frequency response which varies between two user specified curves, an on-axis response and a 180-degree off-axis response, varying smoothly by angle of incidence.

Those tools would be a huge help in answering the questions I’m posing here by providing the ability to hear these things in real-world situations by isolating the differences to only these issues without such a wide range of other complications.  It won't make the Tetramic a practical answer for the particular microphone array application I described earlier, but it would definitely provide a way of getting real-world answers to these conceptual questions and is likely to have other real-world recording applications.

Glad to hear some new things are in the works at Core Sound in regards to the Tetramic. As a longtime Tetramic user, here are two basic issues I urge you to address to make the Tetramic more user friendly:

1) VVMic for TetraMic (and VVTetraVST) needs the ability to do basic A-format channel-matching gain adjustment in the standalone application.  This is a basic, critical A-level function. The user should be able to input test tone files made during a particular session for mic-preamp level calibration, determine the gain offset between each of the 4 files, and adjust for that in the application immediately prior to the A-format conversion.  To do so it would simply require a signal level offset detector and individual A-format channel gain controls.  The user should not be required to first import A-format test tone files to an editor, determine the gain offsets between channels, then import the audio A-format files, apply the calculated gain adjustments to them and export the files with those changes before being able to do an A-format conversion on them. 

2) A small, single-box power supply eliminating the need for the four separate power supply boxes and the mess of cabling.  It should have the option of either battery or P48 powering, with a 6pin mini-xlr input and a single mulit-pin output with various breakout cable options to suit various recorder inputs (XLR, ¼” TRS, unbalanced 1/8” TS plugs, etc).

[edit- Okay, after typing the bit above I just checked the Coresound site and it looks like you are providing some additional powering options with the new PPA3 and PPAc options.  The PPA3 effectively addresses simpler P48 powering.  What is still needed is a simple single-box battery supply, allowing any 4channel recorder to be used regardless of phantom powering.  That would make Tetramic>battery-box>Tascam Dr2d (4ch via two 1/8” inputs) the smallest/simplest ambisonic recording system available.]
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<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Gutbucket

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Neumann M50 for Decca Tree arrays immediately spring to mind.

http://repforums.prosoundweb.com/index.php?topic=36013.0

http://repforums.prosoundweb.com/index.php?topic=2413.0

Fran

Yes. That's a good example of a microphone which has a directional response that is not uniform across its frequency range, yet is highly desirable for some applications partly because of that trait.

To continue the latest ambisonic twist on all this, a simplified/idealized version of that M50 polar response behavoir (pressure omni mounted in a spherical housing) could be relatively easily modeled by ambisonic B-format manipulation techniques.  Len, do you know of any B-format software tools which offer that?  It could be modeled in the B-format tool I asked about above, one which allows the user to "Specify a changing polar response which varies between any two first order patterns, smoothly by frequency".  In this case, omni up to the corner frequency where the size of the spherical plastic housing around the capsule becomes acoustically significant, then smoothly morphing to a more directional pattern on-axis at frequencies above that. 
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<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Gutbucket

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Perhaps.  Are there no balun components in the receiver necessary to convert the CAT5/6 run to mini-plug appropriate?  But yeah, that's a step closer to what I'd like for more minimal setup for powering the TetraMic.   Still requires a seperate external battery though, so perhaps not significantly different enough in size, weight and complexity from 4 x PPA2 boxes gaff-taped together into a block, which is how I currently power it.

What TetraMic needs is a simple battery box with two 6-pin mini XLRs.  One for input from the existing 6-pin mini-XLR terminated mic cable, the other to a 2 x miniplug output breakout (in my case, or whatever output terminations are appropriate)

In Niaint product line terms, it needs a 4channel PIPsqueek.  The 3 position global gain switch and independant channel gain balancing feature would be perfect for running a TetraMic into a DR2d.  The entire ambisonic recording system would fit in one hand.
« Last Edit: August 04, 2014, 06:01:52 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<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Gutbucket

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In a similar vein to my speculation about the possible usefulness of an off-axis response which is 'loudness curve' shaped, here's another observation from looking at the responses of existing microphones.  It may or may not be useful, but what about a flatter 'free-field' on-axis response with an elevated high-frequency 'diffuse-field' off-axis response?  Sort of the opposite of the typical real-world omni high-frequency directional response exaggerated in the M50.  I can't see that being useful for distance mic'ing, but it might be for closer mic'ing of a source where a free-field response is appropriate, while retaining diffuse-field ambient pickup qualities.

Although it's not free-field equalized on-axis, the on-axis/off-axis response difference of my Gefell M94 cardioid capsules looks a bit more like that, with much less low frequency 'loudness curve' and a touch more diffuse-field-EQ-like 9kHz emphasis in the 180-degree off-axis response than their M300.  Granted that in comparison, the on-axis low frequency response of the M94 drops compared to the M300, so its 180-degree off-axis is lower by that same amount, but even so, the difference between the curves is less than the more loudness-like 180degree off-axis curve of the M300 cardioid.

MG M300 cardioid microphone (180 degree off-axis response more loudness-curve like)-


MG M94 cardioid capsule (180 degree off-axis more diffuse-curve like, even if one imagines both these curves modified once the on-axis is normalized to match the M300 curve)-

« Last Edit: August 04, 2014, 06:05:28 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<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Len Moskowitz (Core Sound)

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Can you point me to any B-format tools which can do the following?

1) Specify a changing polar response which varies between any two first order patterns, smoothly by frequency.
2) Specify a changing frequency response which varies between two user specified curves, an on-axis response and a 180-degree off-axis response, varying smoothly by angle of incidence.

I'd suggest asking these questions on the sursound mailing list.

Quote
As a longtime Tetramic user, here are two basic issues I urge you to address to make the Tetramic more user friendly:

1) VVMic for TetraMic (and VVTetraVST) needs the ability to do basic A-format channel-matching gain adjustment in the standalone application.

For this very reason we recommend using a recorder (or mic pre-amps) that have digitally-set gains, so that the four channels are easily matched and don't require an external tone reference nor level matching in post. These include the Tascam DR-680, Sound Devices 788 and others.

But as you point out, this feature would be nice for the lower cost recorders that lack digitally-set gains (like the Zoom H6 and the Tascam DR2D). We'll talk about it within the TetraMic project team.

Quote
2) A small, single-box power supply eliminating the need for the four separate power supply boxes and the mess of cabling.  It should have the option of either battery or P48 powering...

Our recently introduced PPAc system provides this. The PPAc transmitter has a DC input jack so you can power TetraMic with an external battery pack instead of P48.

We've initially offered the PPAc receiver with four XLRs, for balanced output. It's simple enough to add adapters (Hosa offers them) to go from the balanced XLRs to unbalanced 1/8-inc (3.5mm).

If there's enough interest we could offer a PPAc receiver with a pair of 1/8-inch stereo plugs (unbalanced).

« Last Edit: August 06, 2014, 12:46:02 PM by Len Moskowitz (Core Sound) »
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Offline Gutbucket

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Thanks, I'll ask about that on the sursound list.  Haven't payed much attention to the list for the past couple years.  I believe those types of decoders would open up previously un-tapped capabilities and provide advantages for ambisonic systems like TetraMic that are under-explored as far as I know.  I have little doubt that the researchers on that list are are way ahead of me on this conceptually.  An easy to use tool to do it is what we need.

And yes, the huge advantage of digitally set gains and the channel ganging feature which maintains the gain relationship across all 4 channels used by the TetraMic was a big factor in choosing the Tascam DR-680.  I have the raw files stored as A-format along with the calibration tones for all recordings made with the R-44, rather than the converted B-format files, simply because it was too much hassle at the time of archival to check and adjust levels before doing the B-format conversion correctly.  Those will need to be adjusted once they are revisited. 

Just as best practice, I typically store calibation tones with the TetraMic recordings made with the DR-680 files as well.  Have you found the digital gain tracking remains close enough across all channels to make doing that unecessary with the Tascam DR-680?
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<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Len Moskowitz (Core Sound)

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Have you found the digital gain tracking remains close enough across all channels to make doing that unecessary with the Tascam DR-680?

Yes, although there have been very rare exceptions.
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Re: Cardioids which are most natural sounding off-axis? On-axis sound secondary.
« Reply #26 on: September 04, 2014, 11:27:19 AM »
Was reading this months Pro Sound and they had an interesting article in regards to surround - side and rear ambiance added to a recording.

SoundField SPS200 Surround Sound Microphone (  http://www.prosoundnetwork.com/article/studio-review-soundfield-sps200-surround-sound-microphone-by-rob-tavaglione/18223  )

Expensive as expected, but I found interesting the software for this mic to shape the sound post recording as well as the comparing of other mic's.

Not exactly on point with the start of this thread, but interesting in re. to the capture of surround technology.
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Offline Gutbucket

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Re: Cardioids which are most natural sounding off-axis? On-axis sound secondary.
« Reply #27 on: September 04, 2014, 01:13:49 PM »
Single point ambisonic microphones are conveneint and unbelievably flexible, great for 2-channel stereo, but IME are not ideal for optimal multichannel surround sound recording of music when used alone, as they rapidly suffer from lack of sufficient channel seperation as the channel counts increase.  They are sufficient practical solutions for less critical surround recording jobs like TV or film sound ambiances, but not for critical music listening. 


It's limited by the physics and geometry.  It's simply impossible to cram more than a few virtual first-order microphones into the same point without their patterns overlapping too much.  They are great at doing 2-channels, acceptable for 4 channels, not very good at 5 channels (requires delaying the virtual rear channels to provide sufficient diffuse decorellation), and unacceptable for more than 5.  Good live multichannel surround recording pretty much requires spacing between microphones to make up for that first-order directionality problem.  One could of course use more than one ambisonic microphone as Len mentioned previously, or use a combination of an ambisonic microphone with standard single channel microphones.
« Last Edit: September 05, 2014, 12:00:48 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<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

 

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