Hi Aaron, Many thanks for the link to Ron Streicher's article -- I passed the link along to my friend who is a big advocate of the Decca Tree. I've listened to demonstrations of the precedence effect, and they always involved a single sound source (such as a talker) coming from two loudspeakers. The signal to one loudspeaker was delayed, but slightly greater in level. The sound appears to come from the non-delayed speaker despite its lower SPL. I'm writing off the top of my head, but I believe level difference can be 6 dB or greater (up to 11 dB?) and the sound will still appear to come from the non-delayed speaker. What makes the Decca Tree interesting, then, is that when recording is mixed to two channels, there's a phantom (center) image that serves as the non-delayed source. In other words, both speakers (L+R) are same distance from listener, and level is the same, too, to create the central image. But keeping the image stable (as it's touted) is accomplished by virtue of the L+R signal being slightly pushed ahead (time-wise) of the extreme L or R signals. This delay is made possible by a slightly forward mic in the recording setup. Now I'm curious to use two speakers to demonstrate the precedence effect, but using the L + R signal as the delayed signal (or visa versa) and seeing whether the source will continue to have originated from the non-delayed speaker or phantom image. I know time differences are used in panning, but they're generally *weaker* than level differences. In comparison, the precedence effect isn't subtle, but it does wear off after the onset of a sound, and level becomes the dominant localization cue--at least that has been my experience. I haven't heard a single-source demo of the precedence effect that uses a phantom image as the delayed or non-delayed source--the sounds have always come from discrete speakers/locations. Thanks again for help and link. Best, Eric C.
________________________________ From: Aaron Heller <hel...@ai.sri.com> To: Eric Carmichel <e...@elcaudio.com>; Surround Sound discussion group <sursound@music.vt.edu> Sent: Wednesday, June 26, 2013 11:06 AM Subject: Re: [Sursound] Giving Precedence to Ambisonics Ron Streicher has written about using a Soundfield as the middle mic in a Decca tree http://www.wesdooley.com/pdf/Surround_Sound_Decca_Tree-urtext.pdf and Tom Chen has a system he calls B+ Format, which augments first-order B-format from a Soundfield mic with a forward ORTF pair. I've heard it on orchestral recordings at his studio in Stockton and it sharpens up the orchestra image nicely. Aaron Heller (hel...@ai.sri.com) Menlo Park, CA US On Wed, Jun 26, 2013 at 10:02 AM, Eric Carmichel <e...@elcaudio.com> wrote: Greetings All, >I have a friend who's an advocate of the Decca Tree mic arrangement. Many of >his recordings (a lot of choir and guitar) sound quite nice, so I looked into >aspects of the Decca Tree technique. For those who may not be familiar, the >*traditional* Decca Tree arrangement is comprised of three spaced >omnidirectional mics. A center microphone is spaced slightly forward. From >what I've read thus far (Spatial Audio by Francis Rumsey, Focal >Press; and selected articles in the AES Stereophonic Techniques Anthology), >the slightly advanced time-of-arrival for the center mic stabilizes the >central image due the precedence effect. However, the existence of the third >(center) mic can result in exacerbated comb-filtering effects that can arise >with spaced pairs. So, to avoid these filtering effects, bring on a Soundfield >/ Ambisonic mic...?? >As I understand, Ambisonics already takes into consideration known >psychoacoustical principles, and is why shelving is used to *optimize* ILDs >and ITDs above and below 700 Hz, respectively. But as many readers may know, >there are some nearly unpredictable ILD/ITD effects at approx. 1.7 kHz (for >example, see Mills, 1972, Foundations of Modern Auditory Theory). Creating a >virtual Decca Tree seems straightforward. To move the center channel, or a >virtual mic *forward* would require little more than offline processing. I >wonder whether anybody has tried the following: Slightly delay all channels >except the signal (or feeds) that make up the forward-most (central) channel. >Using an Ambisonic mic would eliminate combing effects. I realize a number of >Ambisonic plug-ins have built-in crossed-cardiod, Blumlein, and spaced omni >functions, but not sure I've seen any of them give *precedence* to the >precedence effect or Decca Tree arrangement. >Two-channel playback (both convention and binaural) is here to stay for a >while, so optimizing Ambisonics for stereo is desirable to me. In fact, one of >my favorite recordings from the late 80s was made with the band (The Cowboy >Junkies) circled around a Calrec Soundfield mic. I've never heard whether the >Trinity Session recording was released in a surround format, or if the mic's >hardware decoder converted straight to stereo from the get go. That particular >recording made me aware of the Soundfield mic, though surround sound wasn't an >interest for me at that time. >If anybody I had attempted the Decca Tree using an Ambisonic mic (even with >addition of a separate and forward omni mic), I'd be interested in knowing >what your experiences were. >Many thanks for your time. >Best, >Eric C. (the C continues to remind readers that this post submitted by the >*off-the-cuff* Eric) >-------------- next part -------------- >An HTML attachment was scrubbed... >URL: ><https://mail.music.vt.edu/mailman/private/sursound/attachments/20130626/535efc06/attachment.html> >_______________________________________________ >Sursound mailing list >Sursound@music.vt.edu >https://mail.music.vt.edu/mailman/listinfo/sursound > -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20130626/ef2e8691/attachment.html> _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
