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Author Topic: AUD/SBD Delay  (Read 1091 times)

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Offline Gutbucket

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Re: AUD/SBD Delay
« Reply #15 on: September 15, 2021, 06:13:27 PM »
As I understand it, it's basically a series of rapid delays.  Each identical to the dry SBD signal, but with various levels with an an overall attenuating trend, and with various pannings.

So a delay more than a 'verb thing.. convolution could do it of course, but so could a basic digital stereo multi-tap delay.  The 100% wet thing is just a way of initially lining up the direct-arrival impulse of both AUD and SBD like we typically do, but then only letting the SBD contribution occur during the early reflection time zone without having to do a subsequent time shift.
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Offline opsopcopolis

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Re: AUD/SBD Delay
« Reply #16 on: September 15, 2021, 06:16:36 PM »
Even more esoteric, yet potentially more applicable for tapers using traditional AUD microphone setups as well as OMT microphone arrangements-

There is a technique for mixing orchestral spot microphones with the main microphone channels that I believe might also be applicable to the SBD part of a matrix.  After all, a SBD feed is essentially a collective stem of close spot mics.  This technique treats the AUD as the foundation of the recording - Like a classical main microphone pair, aiming to preserve it's primary role and imaging qualities.  It essentially treats the spot (SBD) signal in such a way as to emulate and reinforce the early-reflections part of the graph I posted above,  letting the main pair provide the initial direct-impulse and reverberation parts.

It time-delays the spot mic (SBD in our case) so that it's initial impulse is aligned with the main (AUD) pair, but routes that through a multi-tap stereo delay/reverb unit set in such a was as to emulate random early reflections.  The unit is is set to 100% wet, eliminating the direct impulse, and set to provide no reverb or tail, leaving both of those parts to the main (AUD) pair alone.  It produces only a series of short dry delays, each randomly panned and with random decreasing levels within the appropriate time range (note the downward trend and range of amplitudes in the early ref. portion of the graph above), mixed in with a level lower than that of the direct signal from the main (AUD) pair but higher than the reverberant tail.

Ironically, this actually delays the SBD to be slightly behind the AUD, but only by a few milliseconds.  This is what preserves the stereo imaging cues provided by the AUD pair.

This technique would apply only to an already great AUD that might be made even better with some clarity sweetening.  It might also work as a way of effectively stereoizing a mono SBD. I have a paper on this somewhere and will search for it.  A brief online search didn't pull it up.


This is genius!
I've always made sure that my SBD feed happens before the audience mics, but the early reflection technique is a way to get around that, and preserve the natural stereo image.
Just to clarify, in this technique, there would not be ANY direct soundboard feed used, only the 100% wet early-reflected convolution of the dry feed?

Not sure about the classical use case, but you can do it both ways. Plenty of verb plugins include "early reflections" and using a 100% wet early reflections verb bus is generally great way to create space on DI'd instruments, so I'd assume it works the same way here.
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Offline Gutbucket

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Re: AUD/SBD Delay
« Reply #17 on: September 15, 2021, 06:33:13 PM »
Found it.  G√ľnther Thiele's Room Related Balancing Technique-

Link to the original 1990 paper (scanned) available at the Hauptmikrofon site:
https://hauptmikrofon.de/theile/1990-10_Room-related-Balancing%20_88.AES-Preprint2886.pdf

I came across it in a later 2001 paper of his on multichannel recording.  This one is well formatted, easier to read and has better illustrations of the idea.  Skip to page 36 for the relevant section:
https://hauptmikrofon.de/theile/2001-2_Multich.-Recording_Nordic-Symp.-2001.pdf
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 Scooter123

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Re: AUD/SBD Delay
« Reply #18 on: September 19, 2021, 10:04:25 PM »
If already time aligned on the same deck, then just find a nice clean high frequency transient (think hi-hat) and align on that.

+1

I trust my eyes to a wave form, more than mathematics, or my ears.  Then again, Mr. Hose is my time alignment guru. 
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Offline Gutbucket

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Re: AUD/SBD Delay
« Reply #19 on: September 20, 2021, 11:00:59 AM »
I reread the papers I posted above, along with a couple others, and my main take away remains: Align by eye, confirm and tweak by ear (bumping it back and forth a bit by a few ms to confirm the sweet spot) as being a good practical approach.

Not sure how applicable the Room Related Balancing thing is for TS tapers.  It's mostly about preserving depth cues present from the main pair (AUD in our case) to present a more convincing illusion of source depth upon playback.  That's not especially important or desirable for most TS tapers recording PA amplified performances where a primary intent of mixing in some SBD is increasing the sense of proximity / decreasing the sense of distance from the source in addition to reinforcing clarity and detail.

Thinking back about listening to my recordings and those of others, I can't recall hearing any real sense of depth within the source at PA amplified concerts.  There is depth in audience and hall sound which can be good, and the overall sense of distance to the source which is generally best minimized as much as possible, but little if any depth of sources withing the band itself.  Of the times I can recall such a perception of depth it was problematic - electric jazz acts in classical halls, not fully PA'd where some performers are clear but others are lost in distant mush, comes to mind.  Were I do hear and value a great sense of depth is with non PA amplified acoustic music, particularly classical music in a good hall.  Getting a clear sense of front/back depth without loosing too much clarity and detail of the more distant sounding stuff in back is one of my favorite things to get right with an orchestra.  Everything on stage sounding equally close and clear just doesn't sound correct or natural for that, it looses a delicious 3-dimensional sense of reality, unlike PA amplified stuff where that is more or less the expected goal of a good AUD/SBD mix and any sense of depth within and between the various sources is derived from effects and reverb.

Regardless, one's listening preference comes first so the align by eye, tweak by ear approach applies either way. 

In that light, I take the Room Related Balancing technique to be most useful as a way of understanding what's going on, more than an approach that applies necessarily to the kind of taping most are doing around here. 

It might apply in circumstances where upon dialing in the best AUD/SBD balance everything sounds appropriately clear yet otherwise too flat and soundboardy, as a way of retaining that SBD clarity yet gaining some depth.  Sort of the opposite of the way in which I generally use SBD as clarity seasoning, yet the way many tapers mix things using more SBD and less AUD.
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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