There's loadsa good stuff being discussed here. If I can comment on just one or two ....
> When listening to this through a speaker rig, we hear this boost and tend to interpret it as meaning the sound is close especially in a dry acoustic with a Greene-Lee head brace etc., etc.,. However, surely (unless I am being more dense than usual tonight) this is a learnt response based on the behaviour we have heard from directional mics? After all, taken individually, at those sort of frequencies our ears are essentially omnidirectional and not subject to bass boost (to anything like the same degree). You can test this. Blindfolded your victim, creep up to him silently & whisper in one ear. He will report significant proximity effect. Eric, Duda & Marten will explain this happens cos our lugholes are spaced and form a crude (?) left/right velocity sensor. ________________________________ Robert, Guru Fons has explained with his usual precision some of the limitations of the soundfield. The important question, however, is, "what effect does all this have on the listener in the middle of a Classic Ambi system?". The answer to both the "whisper in your TetraMic/Soundfield" and motorcycle examples is "closeness is exaggerated." If you've got any Soundfield or TetraMic recordings where you've had to place the mike near or surrounded by the audience, the chap unwrapping sweets, rustling his programme or coughing always sounds as though he is directly next to the mike. ________________________________ Mr. Hunt, I hope Sampo & Fons have been sufficiently enlightening. A Classic Ambi rig or soundfield mike has no concept of a "unit circle". They record & present distance as presented to them. The mike cos Helmholtz etc and the Classic Ambi rig with tricks like NFC. Even simple 1st order Classic Ambi rigs with NFC do a good job at plane wave reconstruction at LF. For a synthetic source to replicate this serendipitious situation, you have to 1) Add proximity for close sources or motorcyles as the Encoding Eqns in Appendix of "Is my Decoder Ambisonic?" This is the most important (only) cue available for close sources in anechoic conditions 2) Add a suitable reverb pattern as MAG's "Distance Panners". You need to do this not cos 1) dun wuk but cos real life distance perception is TERRIBLE under anechoic conditions. Ambisonics is probably the best "I am there" system cos it's isotropic nature reproduces reverb and other diffuse fields 'accurately'. This was one of MAG's obsessions, even with stereo. 3) For very far souces, you might want to add HF absorption etc but this is probably out of the realm of the sources you want to simulate. ________________________________ On heretical NFC HOA, there is a far simpler encoding system which avoids overload at LF and doesn't assume any speaker rig. ie pure encoding. This is to treat encoding as you would if you were designing a HOA mike. For this, you MUST roll-off the LF at higher orders cos S/N. This conveniently avoids the LF overload too. But in any real playback situation, you only need HOA at HF so you don't actually lose much useful info. All you have to do is to ensure the phase response of your LF roll-off is replicated by appropriate all-pass networks in the lower orders. There's no need to even specify the LF roll-offs. Building NFC into encoding (ie NFC HOA) should be a de-pinnaeable offense. Keep encoding & decoding separate & clean please.. _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
