Greetings to All: Several months ago I had suggested making a recording of an Ambisonics recording using an Ambisonic mic centered in an array of six or eight loudspeakers. I was curious as to whether the second-generation recording would retain the original recording’s (perceived) directional cues. This project, as well as several of my projects-in-work required that my TetraMic be rotated on its center, vertical axis. There are a number of ways to achieve this, to include a U-shaped fixture that could be attached to the Audix shock mount (used to hold the TetraMic), allow room for the mic’s cable, and then be affixed to a turntable.
Just by dumb luck, I found an easy solution to centering the TetraMic in my arsenal of spare parts. In turns out that the Brüel & Kjær clamp used to hold 1/2-inch mics in KEMAR (or similar acoustical test fixtures) fits nicely around the base of a TetraMic’s brass handle. The B&K clamp is easily bolted to a frame that makes centering and leveling the mic over a turntable or tripod ball head simple. The fixture I built also holds the four TetraMic XLR adapter/preamps. You can see photos of my handiwork by going to elcaudio.com/research/page_001.htm Side note: There is no link to the above photos from the homepage: I’m way behind updating both of my sites (= cochlearconcepts and elcaudio). The test room shown in the photos is a semi-anechoic room with treatment on all walls, the floor, and ceiling. My thanks go out to William (Bill) Yost, PhD for allowing me to use the room. Briefly, I wanted video and dry voice recordings of speech stimuli for an upcoming study. I made video recordings (from two angles) of the talkers to complement the speech stimuli. While I had access to the semi-anechoic room, I made a few recordings using my TetraMic so that I could initiate the aforementioned recording-of-a-recording project. Instead of using an array of loudspeakers or a “natural” environment to create the first-generation recording, I used a single loudspeaker in a fixed location and rotated the TetraMic on its vertical axis. The Bilara ball head seen in the photos has tick marks that allow accurate rotation in 15-degree increments. The distance from the loudspeaker to the TetraMic was 2 m. For each angle, the same sequence of tone bursts was presented and recorded. There are a lot of test signals that could have been used, but I chose to use 1/6-octave pure tones ranging from 50 Hz to 15 kHz. Tones were generated using a popular acoustic analysis application (Arta). It was interesting to note that I could hear clicks at the ultrasonic frequencies (which for me is anything above 14 kHz). Time-domain analysis of the Arta-generated tones revealed that the 1/6-octave sine wave bursts don’t have rise or fall-time envelopes, and that the tones can end abruptly anywhere in their cycle. I ended up applying rise and fall times so that I could use the tone bursts in future listening experiments. Localizing a click is a lot different from localizing a pure tone because the pinna transfer function may be more dominant than ILDs or ITDs when localizing complex (e.g. click or transient) sounds. The click is probably masked at audible frequencies, but the subsonic, transient information could still provide a localization clue (could be interesting to find out). Well, I have a lot of recordings, both audio and video, to sort through. I’ll make another post once this is completed. I’ll also make the recordings available at a later date. Best, Eric -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20120813/9fd1d9aa/attachment.html> _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
