Thank you both for your answers! That helps a lot. So, what i'm understanding is that more speakers will give you less 'holes' in the sound field and more channels will give you a more realistic sound field in a larger room with more people. So 4-channels would suffice for a few people in a mid-field environment, you'd want more for a larger room and more listeners? Or.. where does one apply this channels vs speakers when talking about playback vs recording? Uh...
Bearcat On Thu, Apr 25, 2013 at 4:03 PM, Fons Adriaensen <[email protected]>wrote: > On Thu, Apr 25, 2013 at 02:50:24PM -0600, Bearcat M. Şándor wrote: > > > As i'm still learning about Ambisonics (mostly trying to wrap my fuzzy > head > > around the math), there's something i don't understand. > > > > If the 4 channels of a b-format mic give you all you need for the > > mathematical computations for 3-D space, why do we have Ambisonic mics > with > > more than 4 channels and orders with 8, 16 and more channels? What does > > having a 4 channel (w, x, y and z) mic restrict you? > > There is no simple answer to your question. > > As Sampo as already pointed out, first order AMB signals provide > all the info there is about the sound field in a single point. > The physics and maths being what they are, they also define the > sound field in an area around that point. The size of that area > depends on the frequency. For first order the 'extrapolation' > works well up to a distance of around 1/4 to 1/3 of a wavelength. > So the area it covers will be quite large at low frequencies (LF), > but gets very small for medium (MF) and high (HF) frequencies. > Above a few hundred Hz it is so small that it is impossible even > for a single listener to have both ears inside the area in which > the sound field is accurately reconstructed. > > So for MF and HF Ambisonic decoders use an ad-hoc approximation > which is based on psycho-acoustics and which works well in practice. > That is the reason why you need a frequency-dependent decoder, > either dual-band or using shelf filters. So far for first order. > > Higher order Ambisonics provides two things. First, the area in > which the sound field is reconstructed 'exactly' becomes larger, > more or less proportional to order. But in practice little is gained > from this and we still need the 'approximation' for the mid and high > frequency range. But HOA also allows this approximation to be much > more accurate, to the point that for third order or above, in practice > it can be 'almost perfect'. This allows HOA to work in a much larger > listening area than first order, i.e. to serve a large audience, and > also to be usable in situations were for practical reasons (related > to speaker placement) first order would not work well. > > To really fully understand the why and how you'll need the maths. > What I wrote above is an attempt to explain things in intuitive > terms, which means to simplify things, but hopefully not to the > point where the essence is lost. > > Ciao, > > -- > FA > > A world of exhaustive, reliable metadata would be an utopia. > It's also a pipe-dream, founded on self-delusion, nerd hubris > and hysterically inflated market opportunities. (Cory Doctorow) > > _______________________________________________ > Sursound mailing list > [email protected] > https://mail.music.vt.edu/mailman/listinfo/sursound > -- Bearcat M. Şándor Feline Soul Systems Voice: 872.CAT.SOUL (872.228.7685) Fax: 406.235.7070 Jabber/xmpp/gtalk/email: [email protected] MSN: [email protected] Yahoo: bearcatsandor AIM: bearcatmsandor My public pgp key is included for verification of my identity -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20130425/4a8faaf3/attachment.html> _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound
