For Sursound subscribers, the ideas of virtual microphones and binaural recordings via Ambisonic recordings is old news. But there are a lot of hearing scientists, sound designers, recording engineers, and surround-sound enthusiasts who are not familiar with Ambisonics and what it offers. One way of using Ambisonics for research requires no loudspeakers at all (which is a plus when dealing with budget and limited space). I just sent the email (below) to colleagues who are not familiar with Ambisonics, VVMic, etc. with the hope that they find the idea purposeful. People on this list may have suggestions as how to improve on my idea. Thoughtful ideas and constructive criticisms always welcome. Best, Eric
Greetings to All, I hope you will take a moment to review this email, as I believe the idea outlined herein has a lot of research potential. I have also provided links to sample recordings that I made yesterday (November 7). Imagine that we had the technology to create a "perfect" acoustical replication of restaurant noise (3-D, of course), and we wish to use this acoustical replica to simulate cochlear implant (CI) or EAS listening in a 3-D listening environment. One thought might be to put a mock processor or HA body on a listener's head, and vary the mic settings (omni, directional, etc.). The mic's output would next be routed through a vocoder or other simulator, and the resulting electric signal would be routed to an insert phone placed in the normal-hearing listener's ear. Now the listener is free to move his/her head in our controlled 3-D listening environment while, at the same time, make adjustments to the mic's pickup pattern (as well as processor settings). Two (of several) obvious flaws with this idea are: 1) We don't have a perfect replica of a 3-D listening environment, and 2) It would be impossible to block out the acoustical stimulus, even with the use of foam plugs and insert phones. We could correct for the second problem by simply recording what comes through the HA mic or mock CI processor's mic, but then we'd have to make separate recordings for every mic pattern as well as head position. We could have used a KEMAR from the very start, but then we couldn't have captured the same live "event" each time we switched to another microphone type or head position. I believe the best solution can be obtained from mathematical extraction from Ambisonics-recorded surround sound wav files. When done correctly, all directional information is contained within an Ambisonics recording. All that is needed, then, is a way to create virtual microphones that can be steered in any direction (in the digital, not acoustical, domain). This is relatively easy to do via VVMic, and first-order pickup mic patterns are also a snap to create. What one has to be careful of is that mic polar responses are 3-D, too (noting that most polar plots are shown in 2-D). With the right software (which I'm working on), we can add head tracking. Head tracking is already popular when used with binaural recordings. But you have to look closely at what's being proposed here: I am creating ELECTRIC (2-D) listening as it might be perceived in a 3-D environment. The L or R channel of a binaural recording will roughly give the equivalent of an omni mic placed at or in the ear canal, but this hardly qualifies as a realistic simulation of CI mic placement or type. What I am proposing will provide a lot more flexibility and CI realism than an omni mic placed at the concha. When more than one mic or mic pattern is used, as would be the case for EAS, we can just as easily create a variety of mics, mic orientations, and mic polar responses from a single master recording. No speakers are needed, so there's no speaker distortion, combing effects, or other anomalies. Here's an example of what can be done: I made a recording in a cafeteria yesterday. The unprocessed recording can be heard by going to www.elcaudio.com/research/unprocessed.wav Using appropriate software (VVMic, Harpex, and other VSTs) to steer a virtual cardiod mic away from me (the talker) yields the wav file below (directional_mic_01.wav). Note that this isn't merely deleting a channel or channels, nor is it panning L or R. I can steer the mic up, down, sideways, front, back, or any direction in 3-D space that I wish. www.elcaudio.com/research/directional_mic_01.wav Steering the virtual (cardiod) mic towards me when using the same master-recording segment (for direct comparison to the above) yields the following wav file: www.elcaudio.com/research/directional_mic_02.wav The next step is adding the mic's response and directional characteristics to an HRIR so as to include head shadow. At present, I can turn the master recording into a binaural recording using over 50 HRIRs (via Harpex), or I can create an unlimited number of microphones and mic directions along with 1st-order pickup patterns (e.g. VVMic), but not both mikes + HRTF (other than omni mics at the concha). I believe this can be worked out mathematically, and the outputs of multiple virtual mikes plus appropriate processing could be used to create the ideal CI or HA simulations using real-world scenarios (obtained from my library of live Ambisonic recordings). Best, Eric -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20121107/4646a4f4/attachment.html> _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
