Well, don't get the idea that I do not like Blumlein. My once(actually twice as it happened) in a lifetime chance to record major orchestras with Kavi Alexander in charge, we did use Blumlein. And ORTF sounds a little colored as to timbre to me (we have some recordings made with identical mike placements but the two methods, though this is hardly a theoretical test since the mikes themselves are of necessity different).
But I have always been told as "conventional wisdom" that ORTF gets the time of arrival right in a way that Blumlein does not. And I always regarded the choice as a tradeoff--absolutely spot on timbre with Blumlein versus correct space with ORTF. But maybe this is wrong! If things work up to 6k, that would surely alter the viewpoint. I await this with interest. I would also be interested to see the calculations that would explain why ORTF comes out a bit colored, at least to my ears. Robert On Mon, 2 Apr 2012, Eric Benjamin wrote:
I can't answer the question precisely without either doing an experiment or by doing many hours of calculations. But one thing to consider is that the Blumlein recording won't fail to produce correct ITDs at frequencies above 700 Hz. At least, not theoretically. I can demonstrate by calculations using a good head model that the ITDs continue to be correct up to some relatively high frequency, say up to 6 kHz. I have the calculations already done to demonstrate that is works for an Ambisonic system. But one of the differences between theory and practice is that the listener won't necessarily be exactly at the sweet spot. That is to say, if the listener shifts 10 cm to the left then he has undone the 'correct' time differentials provided by the ORTF system. Don't take this to mean that I don't like ORTF recordings. I do like them. The best stereo recording that I have ever made was an ORTF recording. But then, I'm not a very good recording engineer. I think that one of the reasons that I like ORTF is that it introduces an artificial spaciousness which may compensate for the spaciousness that is lost in stereo reproduction. I will do some calculations on ORTF stereo so that I can understand it better. ----- Original Message ---- From: Robert Greene <gre...@math.ucla.edu> To: Surround Sound discussion group <sursound@music.vt.edu> Sent: Mon, April 2, 2012 1:44:28 PM Subject: Re: [Sursound] Transient time differences Thanks for the information. But here is my question in more precise form: Suppose you do a recording with ORTF(which of course has its own set of problems). Suppose you record a source that is say 15 degrees left of center. and that the source is a pistol shot(an impulse). Now the impulse will arrive at the left mike before it arrives at the right mike. The time difference is the same more or less as it would be for a dummy head recording since the distance between the mikes is the same (more or less) as the distance between the listeners ears(or the dummy head ears). On playback, the impulse will also arrive at the left ear the same amount of time before the right ear-- as far as the high frequencies are concerned. Namely they are heavily shadowed by the head so that the arrival at the left ear first is blocked from the right ear, and the right ear hears only the right speaker. This is in the highs. Below around 700 Hz, Blumlein would have put the phase shifts right and that part of time would be there. But the head shadowed part , the high frequency part, is right for ORTF but wrong for Blumlein-- the direct arrival of the high frequency part of the impulse as recorded in Blumlein is simultaneous in the two speakers(as is everything) but there is no reconstruction via head effect because the head effect is essentially total shadowing. Of course there is some head shadowing in the real world, too. But 15 degrees off to one side is not enough to block the highs so completely as 45 degrees (or 30 degrees). So there is some range of angles where the timing is off because of the greater shadowing(almost complete) from the wide speaker separation is not representing the real situation. Is this wrong? This is not my private theory. I think Blumlein was aware of this, and I known other people have mentioned it. Maybe is does not really matter, but it seems real enough. (I believe it is known that time delays in the high frequencies play a role in location) Robert _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
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