R/E/P > Bruno Putzeys (Designer) - Dave Hecht (Master Tech)

Baffled omnis processing ala Blumlein 1931

(1/4) > >>

ted nightshade:
Hello there,
I just got the New Stereo Soundbook and was reading Blumlein's (amazing) British Patent Application 394,325 in the appendix-

He has this circuit for processing baffled omnis, that turns low frequency phase differences into amplitude differences. Apparently the high frequencies are left as is.

Sucker that I am, I'm still trying to figure out a really gratifying way of recording stereo with two pressure omnis that's mono-compatible (pressure omnis 'cause I'm mostly recording outside, wind and that, and hey I like my lows)- this looks to be it?

If the world followed up on this one, I didn't hear about it. Anybody know what happened? Is there a reason why nobody (that I know of) does this?

If you have the New Stereo Soundbook on hand, the idea is discussed in paragraphs 29-31 of the patent application. I could probably transcribe some of it here if need be.

Thanks!

John Klett:
The New Stereo Soundbook
by F. Alton Everest, Ron Streicher
McGraw-Hill/TAB Electronics; (February 1992)

that New Stereo Soundbook?

I don't have it...

here's the patent for those who want to read it

http://www.doramusic.com/patents/394325.htm

That's an eyeful -  hmmm... drawings...

well - the network is passive sum and difference...  he got a lot of mileage out of that...  oh - this is the vertical and lateral disc recording patent.  All mono in phase is lateral and all out of phase information is vertical.  The is how to make stereo record.  There's a cutterhead.  Cool.

I'm not sure what to recommend re your recording situation.  You can do spaced omni's open but mono compatibility might be a problem.  Sounds good in stereo though.  Max Wilcox (classical and jazz producer engineer) likes spaced omni's.

If you have a pair of omni's closer together - like about 5 inches apart or so - and place a baffle between them - a foot square hunk of 1/4" luan plywood with some 1/2" open cell foam on both sides is a decent place to start experimenting - you are sort of making a simple form of dummy head.  

The wavelengths at low frequencies are so long they will ignore the baffle and reach both mics.  For all intents that information is in phase.  As wavelength gets shorter the baffle becomes more significant and the mics essentially go cardioid.  Our ears are omni but all that stuff around them (head, pina etc.) make 'em more directional simply by blocking and diffracting (refracting?).

Anyway - I've done that baffle trick and it makes a rude but useable binaural recording.  You will get some bass buildup when you add the two mics so the two networks back to back with attenuators in between - shown in the drawings in the patent - can be used to drop the sum signal relative to the difference - I have not tried that but it makes sense.

Haeco (I think that is how it's spelled and that company is long gone) made a box that did a stereo sum to mono and gave you quite a bit of control over the bass buildup.  I suppose that an elliptical filter out of a cutting console could do something helpful there too.  I have some prints for one or more of those somewhere.

People use these sum and difference networks all the time to manipulate the proportion of mono and stereo - as a width control...  and for doing MS recording etc....  It's not a lost art

maarvold:
At NAB there was a brochure at the Schoeps booth called Newsletter No. 6.  Although it doesn't specifically discuss what you're talking about, they discuss a bunch of mic techniques that might give you insight into what you're looking for and why you're looking for it.  Also a lot of good stuff in John Eargle's "The Microphone Book".  If you email me your address, I'll send you the Schoeps booklet.  

Mike Aarvold

ted nightshade:
john klett wrote on Fri, 23 April 2004 13:55


If you have a pair of omni's closer together - like about 5 inches apart or so - and place a baffle between them - a foot square hunk of 1/4" luan plywood with some 1/2" open cell foam on both sides is a decent place to start experimenting - you are sort of making a simple form of dummy head.  

The wavelengths at low frequencies are so long they will ignore the baffle and reach both mics.  For all intents that information is in phase.  As wavelength gets shorter the baffle becomes more significant and the mics essentially go cardioid.  Our ears are omni but all that stuff around them (head, pina etc.) make 'em more directional simply by blocking and diffracting (refracting?).


So that low frequency stuff is in phase. That's good, that was one of my concerns. But I hadn't considered I might end up with more of it than I bargained for (never had that trouble with cardioids!)

Quote:

Anyway - I've done that baffle trick and it makes a rude but useable binaural recording.  You will get some bass buildup when you add the two mics so the two networks back to back with attenuators in between - shown in the drawings in the patent - can be used to drop the sum signal relative to the difference - I have not tried that but it makes sense.

Haeco (I think that is how it's spelled and that company is long gone) made a box that did a stereo sum to mono and gave you quite a bit of control over the bass buildup.  I suppose that an elliptical filter out of a cutting console could do something helpful there too.  I have some prints for one or more of those somewhere.

People use these sum and difference networks all the time to manipulate the proportion of mono and stereo - as a width control...  and for doing MS recording etc....  It's not a lost art




So that's what's going on. I'm so technically illiterate, I couldn't figure that out... I've also been trying to figure out what kinda network is involved in the MS thing, looking at the diagrams but it don't mean much to me... So I ought to be trying to find a good design for a sum and difference network. Or a really fantastic sounding prefab... where to look I wonder- is there a liability to making a super simple design? Maybe a new topic on that...

Thanks!

ted nightshade:
maarvold wrote on Fri, 23 April 2004 23:08
At NAB there was a brochure at the Schoeps booth called Newsletter No. 6.  Although it doesn't specifically discuss what you're talking about, they discuss a bunch of mic techniques that might give you insight into what you're looking for and why you're looking for it.  Also a lot of good stuff in John Eargle's "The Microphone Book".  If you email me your address, I'll send you the Schoeps booklet.  

Mike Aarvold


Very kind of you! Sent you private message.

Navigation

[0] Message Index

[#] Next page

Go to full version