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Author Topic: the Sennheiser pseudo soundfield  (Read 1115 times)

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Offline Nick's Picks

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the Sennheiser pseudo soundfield
« on: June 24, 2017, 09:19:33 AM »
this has been out for over a year now....anyone have any experience with it?
https://www.sweetwater.com/store/detail/AMBEO

long time Soundfield fan......., same array.   All processing done in post.  would love to try one of these some day.
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Offline rumbleseat

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Re: the Sennheiser pseudo soundfield
« Reply #1 on: June 24, 2017, 10:59:01 PM »
I heard a talk at Moogfest earlier this year about 3D sound by some folks at Virginia Tech.  They've put together an enormous hemisphere of speakers on the VA Tech campus called "the Cube", for 3D audio research and performances.

http://www.icat.vt.edu/content/cube-0

At a demo of a "small" hemispheric system at Moogfest, they had a Core Sound TetraMic sitting on the display table and I asked the engineer, Tanner, whether he liked it or not.  He said that it "wasn't the best for localizing sounds".  I'm not sure what he thought would be better or how good the TetraMic really is, or how it compares to the Sennheiser version.

But I'm guessing that Tanner might have opinions on these questions...

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Offline goodcooker

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Re: the Sennheiser pseudo soundfield
« Reply #2 on: June 25, 2017, 01:15:21 PM »
I have had my eye on this. Never fooled around with a four capsule mic but the recordings I've heard from the Soundfield models usually sound nice.

The necessity for 4 matched preamps with exact equal gain is a bit of a hurdle but I wonder if it could be accomplished with the new SD MixPre6 by setting all four preamps to the same gain in the menu. Would make for a small high quality rig with almost unlimited possibilities for mixing in post.

I started a thread about this mic a while back but it didn't get much interest. John Willet did chime in to say that he was disappointed that Sennheiser chose electret capsules for this mic but that's not a deal breaker for me. There a plenty of great sounding mics out there with pre polarized capsules and if they chose one of their P48 caps the mic would probably cost more than double what it does now.
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Re: the Sennheiser pseudo soundfield
« Reply #3 on: June 25, 2017, 11:41:34 PM »
this has been out for over a year now....anyone have any experience with it?
https://www.sweetwater.com/store/detail/AMBEO

long time Soundfield fan......., same array.   All processing done in post.  would love to try one of these some day.

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Offline Gutbucket

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Re: the Sennheiser pseudo soundfield
« Reply #4 on: June 26, 2017, 09:56:38 AM »
TetraMic owner here.  I dig it.

I heard a talk at Moogfest earlier this year about 3D sound by some folks at Virginia Tech.  They've put together an enormous hemisphere of speakers on the VA Tech campus called "the Cube", for 3D audio research and performances.

At a demo of a "small" hemispheric system at Moogfest, they had a Core Sound TetraMic sitting on the display table and I asked the engineer, Tanner, whether he liked it or not.  He said that it "wasn't the best for localizing sounds".  I'm not sure what he thought would be better or how good the TetraMic really is, or how it compares to the Sennheiser version.

This may be as much a comment on 1st order Ambisonic recording and ambisonic playback (that is to say, all tetrahedral single-point ambisonic microphones as sources for their multi-speaker 3D playback arrays) as much as it is about the TetraMic in in particular, in comparison to other 1st order ambisonic microphones.  No 1st order Ambisonic microphone can provide the sharp localization of higher-order ambisonic playback common with synthesized soundscapes and those built from panned monophonic elements within a in higher-order environment.

But those are issues which won't really apply to taperssection users of these types of microphones, where the target listening format is 2-channel stereo.  In that case, these mics are unmatched due to the unprecedented degree of control they provide the to a recordist afterwards via the ability to point a virtual pair of coincident microphones of any 1st order pattern of their choosing in any direction of their choosing.  Some smaller subset of users will use these for recording for multi-channel surround playback.  In that case, these mics offer unprecedented convenience, compactness and ease of use.  That will in many cases trump ultimate playback quality questions. For ambient quadraphonic location sound recording for film and TV (for use in combination with separately recorded dialog, foley, effects, etc) it can be excellent.  Yet for optimal recording of music for surround playback, there is no substitute for non-coincident microphone arrays which use spacing between various microphone elements.  That's a basic, inherent limitation of 1st order pickup patterns and higher channel counts.  For more than 3 or 4 coincident channels, higher than 1st order polar patterns are required to optimize the pattern overlap.  But I'm not aware of other tapers recording for plain vanilla horizontal 5 channel surround playback, much less exotic cubic or hemispheric 3D playback, so the ultimate suitability of these kinds of microphones for high spatial resolution 3D playback isn't going to be relevant to live music tapers.

If you like coincident stereo mics, these things are the ultimate. They work great on stage or at stagelip.  Stick it in the right spot (there is no work around for that), and adjust everything afterwards by ear.  It doesn't even mater which direction the mic is pointing, as long as it is in the right spot.  But you need to be comfortable with adjusting things on the computer afterwards.  That blessing of adjust-ability may be more of a curse if you are a taper averse to having to do post-processing.

One thing which differentiates the TetraMic from the SPS2000 or this Sennheiser mic is the calibration Core does which is specific to each microphone.  That does a lot to correct for variations between individual capsules, as well as correct the overall response of the microphone.  I think Core provides calibration services for Soundfield SPS2000 mic owners now as well.  There was some discussion of that and how it corrected inherent deficiencies in the original SPS2000 response over at Gearslutz several years ago, but I've not followed that discussion in depth.  Same could be done for the Senn version. 

Love to hear the Moogfest and/or VT playback systems, would like even more to play around with them with my recordings. I've never heard true ambisonic playback, and a doubt that many who use these microphone for music recording have either.  I am working towards setting up an 8 speaker cubic array, attached to the vertices of a 10' square pop up tent canopy though.
« Last Edit: June 26, 2017, 10:18:16 AM by Gutbucket »
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Offline Gutbucket

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Re: the Sennheiser pseudo soundfield
« Reply #5 on: June 26, 2017, 10:12:19 AM »
The key to using any of these "recorded A-format" type ambisonic mics is using a recorder which offers "ganged" or "linked" control over the gain across the 4 recorded channels so that the relative gains always remain identical with a fractional dB at all times.  The gain needs to be very closely matched across all 4 channels for the decode matrixing to work.  In practical terms, that means a recorder where then gains can be adjusted to be exactly the same, then locked so that any further change in gain change always effects all four channels equally.

I use the Tascam DR-680 for this.  The Zoom F8 can now do that (after an early firmware update), although it could not initially.

Without that gain-linking feature, using these mics is still possible but far, far less convenient.  The work around requires recording test tones through each channel at the relative gains used during the recording, then using those test-tone recordings to adjust the level of the files afterwards on the computer, prior to conversion from the recorded native microphone output A-format to standard ambisonic B-format or directly to a 2-channel virtual microphone pair output.  If you have to adjust gain while recording without the gains linked across the 4 recording channels, you'll need to make another set of test tone recordings at the new gain settings, then use that to rematch the gains of the resulting files in the computer afterwards.  That's how I had to work when using an R-44.  Much easier to use a recorder that allows a single adjustment in gain which effects all four channels simultaneously and by the same amount.
« Last Edit: June 26, 2017, 03:41:16 PM by Gutbucket »
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Offline Gutbucket

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Re: the Sennheiser pseudo soundfield
« Reply #6 on: June 27, 2017, 04:50:33 PM »
I can imagine a DIY ambisonic mic using Primo cardioid capsules or the equivalent snapped into a tetrahedral capsule mount fabricated via 3D printing.  Indeed in a few early photos of the Sennheiser it looks like such a 3D printed white plastic mount was used during development.  See the photos from the links below with the capsules snapped into it but without lead wires attached.  There are Ambisonic A to B format conversion plugins and other ambisionic manipulation software available to do the matrixing.  The difficult part for a DIY ambisonic mic would be making the appropriate acoustic measurements for calibration files and getting that part of the equation optimized.

http://speedvr.co.uk/sennheiser-ambeo/


http://www.live-production.tv/news/products/sennheiser-springs-action-gopro-developer-program.html



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Offline JiB97

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Re: the Sennheiser pseudo soundfield
« Reply #7 on: June 28, 2017, 01:40:03 AM »

Love to hear the Moogfest and/or VT playback systems, would like even more to play around with them with my recordings. I've never heard true ambisonic playback, and a doubt that many who use these microphone for music recording have either. I am working towards setting up an 8 speaker cubic array, attached to the vertices of a 10' square pop up tent canopy though.

please document this with photos, sounds very interesting
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Offline Gutbucket

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Re: the Sennheiser pseudo soundfield
« Reply #8 on: June 28, 2017, 09:39:53 AM »
It's a slow moving project, but will do so once it starts to come together.

The primary intent has been a portable 6 or 7 channel surround horizontal surround playback system I've thought about putting together for years.  I picked up a hexagonal easy-up type canopy and 7 small DefTech speakers with the intention of internally wiring the canopy frame so I could simply attach the speakers after setting up the canopy and have them in the perfect geometric arrangement, with the speakers attached around the periphery of the canopy at the vertices where the legs meet the accordion frame around the edge of the top. Also picked up an older home theater 7.1 receiver with both HDMI digital LCPM input analog as well as analog RCA inputs to all 7 internal amps.  Haven't gotten further than that so far. 

I then realized I could buy one more speaker and use a standard square easy-up canopy and attach the speakers at the top and bottom of each leg to form a cubic ambisonic playback array.  I could use the LFE channel of the receiver for the 8th channel along with one channel of outboard amplification.  The LFE channel of the receiver has no internal amp, just passes through from RCA input to RCA output, yet is volume controlled along with the other 7 channels.

I've also thought about hanging the TetraMic from the apex of the canopy so it's in the center of a circle of players under the canopy.  Following that thought further, I would be cool to do some room-ambience generation through the playback array while picking, creating a small reverberant acoustic environment for playing outdoors under the canopy.

But one step at a time..
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Offline Len Moskowitz (Core Sound)

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Re: the Sennheiser pseudo soundfield
« Reply #9 on: June 29, 2017, 09:05:45 AM »
We have a short comparison file for TetraMic and Ambeo that we'd be glad to send on-request.

Please send requests to: info@core-sound.com

Re: Location of sound source direction - TetraMic is used as the primary sensor for Marshall Day Acoustic's IRIS system. IRIS is used to design, test and commission concert halls, including the new Phiharmonic Hall in Paris and numerous other halls around the world. IRIS precisely locates and characterizes echoes and reflections. There's lots of good reasons why IRIS uses TetraMic and not any of the other first-order ambisonic microphones, not the least of which is its precision in sound source location and its ability to maintain its precision over time via calibration/re-calibration.

www.iris.co.nz
« Last Edit: June 29, 2017, 09:23:08 AM by Len Moskowitz (Core Sound) »
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Offline Gutbucket

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Re: the Sennheiser pseudo soundfield
« Reply #10 on: June 29, 2017, 10:34:29 AM »
Hi Len, I'd like to check that out. Sending you an email.

I would like want to emphasize to folks here the importance of the mic-specific calibration files that differentiate the TetraMic from the other mics in this class.  That really is the special sauce in the recipe.  Many folks will note other more familiar aspects such as if the microphone elements are pre-polarized or externally polarized, if the output is balanced or not, etc.  Those aspects carry over from the standard microphones we are all familiar with, and are of course not inconsequential.  They may be of more or less importance depending on the application.  However the power of the corrective calibration file approach is not something which carries over from standard microphone tech, and as such is frequently not recognized as being of such significant importance, specifically in the case of multi-capsule ambisonic microphones such as this which rely heavily on the minimization of error through the A to B format matrixing conversion operation required for producing a well behaved output over a wide bandwith.
volition > vibrations > voltages > numeric values | numeric values > voltages > vibrations > virtual teleportation time-machine experience

 

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