Greetings to Everyone, I received some great input and ideas related to my last two post (bi-amping the B-format and subwoofers). Everyone’s input was greatly appreciated. It wasn’t all too long ago that I first learned of Ambisonics, and then this group. At the very start, there was a comment stating that a certain amount of “psychoacoustic trickery” is intrinsic to the Ambisonic decoding. I suppose this is where Ambisonics differs from wavefield synthesis or acoustic holography. Creating a realistic physical space wouldn’t require integration of the duplex theory of hearing in the decoding; it would (somehow) simply re-create the waves as they existed naturally, with or without knowledge of ILDs or ITDs. When we add the 700 Hz ITD-to-ILD switchover as a part of the decoding, we’re assuming the listener will be the “average” human. This is fair enough because Ambisonics and other surround topologies were designed with people in mind. But if we were to design a system to evaluate a “listening machine” (or an animal we know little of), we need something that provides real-world directionality, intensity, and doesn’t care whether humans can or can’t determine the direction of a 40 Hz sound.
But because the transition frequency is 700 Hz for conventional Ambisonic decoders and 400 Hz for domestic decoders (thanks, Martin, for this info), it seems plausible to make this the electronic crossover point as well. The woofers, if properly placed, can handle frequencies that have unambiguous direction as well as the difficult-to-localize low lows. This, then, would be akin to a two- or three-way speaker system, only better: The woofer would receive a signal that is position-specific. So now I’m thinking what Fons and Martin wrote is a plausible solution to my space/channel count/directional lows concerns. Of course, this will require a speaker with a smooth 40 Hz (or lower) to 400 Hz response that can deliver a fair amount of distortion-free energy if the low-frequency sound emanates from an extreme L, R, front, or back direction. Somewhat more clearly: If one speaker has to do the work of six working in concert, it can still manage the signal. I don’t plan on blasting anyone out of the room, but low frequencies originating from well-defined directions do exist in the stimuli. I won’t have to fly the speakers making up the centre (horizontal) array; only the speakers suspended from the ceiling have to chosen based on their weight and size. I’m doing this in a modest-sized room, not an auditorium. Having said all of this, upping my channel count to from 16 to 18 would require a minimal change, and therefore I could provide three horizontal arrays of 6 loudspeakers each. The upper and lower rings/arrays will produce frequencies above 400 Hz only, while the center (horizontal-speaking) array provides the 400 Hz and below energy. (Kind-of like six really stretched out two-way speaker columns, only with Ambisonic decoding for the mids and lows). Other suggestions that I’ll try include adding a Focusrite (or similar) D-A to the system and Reaper software. I’m not sure, though, if Reaper works with MIDI automation, and I use a MIDI-based system of my design to collect data and automate faders. I’ll find out soon enough. There are certainly a lot of ideas to consider. If I didn’t already have a great field recorder, I’d certainly get the MOTU Swiss Army knife... I mean Traveler... in addition to the MOTU 896HD I have now. I already have more than 16 channels worth of analog outs, but not all hardware devices at my immediate disposal share the same software driver. I believe adding a second MOTU and a D-A (Focusrite or Behringer) is a great option. On a wholly different note: Next week I’ll be making an Ambisonic recording in the Superstition Mountain Range, located in Arizona. In the mornings, there’s a low-pitched steam whistle that blows from some type of facility west of the mountain range. There’s quite a delay (at least 5 s) before an echo is heard from one trailhead, but the large cliff face on the mountain and the obstacle-free desert terrain makes for interesting illusion: You’d really believe there’s a second steam whistle up in the mountains. There’s very little “spectral” modification of the whistle's sound as the sound travels across the distance, and both the whistle and resulting echo are loud enough for a good SNR. Curious as to how a recording of this will sound on my home rig. I’ll share the wav files as soon as they’re processed. As always, many thanks to everyone for your time and insights. Best, Eric C. -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20130222/87fb5234/attachment.html> _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
