Re: Some Ambisonics questions

> > - looks like I could use BFEncode2 to encode the
>  > sources, then BFDecode1 to decode onto the speaker ring.
>
> Not sure about the exact ugens
>
>  Also, Josh Parmenter just recently released a new set of ugens you
>  should check out. (JoshAmbiUgensUB.scx in the sc3-plugins, part of
>  the optional installs???).
>
>
>  > * How do I turn many point sources into one single B-format feed? Do I
>  > encode each one separately and then just add the feeds together? (Or
>  > multiply the feeds together? Or...)
>
> You need one encoder for each point source. I believe you can sum
>  the output for all of the encoders the same way you would mix any
>  multi-channel audio, then feed the mixed/scaled multi-channel
>  signal to one decoder.
>
>
>  > * In terms of the audio outcome, is the only difference between the
>  > different "orders" of Ambisonics the sound quality?
>
> Not so much sound quality as "localization quality." Higher order
>  Ambisonics gives a more accurate image of the location of a sound.
>  It also uses more speakers. If you decode a B-format signal to a
>  smaller set of speakers, then you simply throw out the extra
>  localization information.
>
>
>  > * For projecting the ring down to headphones, what is needed? In the
>  > archive there's discussion of downloading the Kemar HRTFs from MIT -
>  > fine. But is there a specific UGen that would take my 8 channels and
>  > apply the HRTFs? Or otherwise how would it work?
>
> I think for this you want Christopher Frauenberger's ambiem package
>
> http://sonenvir.at/downloads/sc3/ambiem/
>
>
> A couple of additional points, ambisonics typically places sound
>  only on the unit circle, so if you want  to work with positions
>  inside (or outside) the circle, most implementations of ambisonics
>  won't support it. Josh's implementation does.
>
>  Ambisonics utilizes all of the speakers, all of the time, to give a
>  sense of location. Some people feel that this system makes it
>  difficult to get a very narrowly focused sound (if that's what you
>  want). Finally, the math behind it introduces delay in some of the
>  signals (by design), so there's a bit of built in reverb.
>
>  Good luck.
>
> -Brian
>
>
>  > ----- Original Message -----
>  > From: "Dan Stowell" <danstowell@...>
>  > To: "SuperCollider users mailing list" <sc-users@...>
>  > Subject: [sc-users] Some Ambisonics questions
>  > Date: Sat, 8 Mar 2008 10:07:47 +0000
>  >
>  >
>  > Hi -
>  >
>  > I've never used Ambisonics before, but I'm wondering about how
>  > possible it would be to implement the following setup using SC's
>  > Ambisonics stuff:
>  >
>  > I have 20 or 30 point sources, each of which has a location in the x-y
>  > plane (and may move about in this plane). I'd like to encode them into
>  > an Ambisonic representation, then decode this to a ring-of-8-speakers.
>  > Then for convenience I'd also like to be able to project this
>  > ring-of-8 down to stereo headphones using a HRTF.
>  >
>  > Looking back over the mailing list archives it looks like this is
>  > probably possible - looks like I could use BFEncode2 to encode the
>  > sources, then BFDecode1 to decode onto the speaker ring. But I have
>  > some questions:
>  >
>
> > * How do I turn many point sources into one single B-format feed? Do I
>  > encode each one separately and then just add the feeds together? (Or
>  > multiply the feeds together? Or...)
>  >
>
> > * In terms of the audio outcome, is the only difference between the
>  > different "orders" of Ambisonics the sound quality?
>  >
>
> > * For projecting the ring down to headphones, what is needed? In the
>  > archive there's discussion of downloading the Kemar HRTFs from MIT -
>  > fine. But is there a specific UGen that would take my 8 channels and
>  > apply the HRTFs? Or otherwise how would it work?
>  >
>
> > I'd be grateful for any tips
>  > Dan
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