Following this discussion of "stereo ambisonics" and comparison with stereo 
pan, I decided to make a simple side-by-side comparison. My .csd is below.

It consists of a 20" L-R-L-R pan, followed shortly by (as close as possible 
to) the same thing in stereo ambisonics. The latter configuration is the one 
Victor recommended, and is the one I use in several compositions. The panned 
version uses the normal 1/4 stored cosine (8193-point table).

The sonic results are very similar. I do at least imagine that the ambisonic 
example is a bit fuller and more spatial. By contrast, the stereo pan sounds 
flat. What do others think?

I like the bit of added richness and openness of the ambisonic example and 
would like it to be available on the XO (soon to be XOXO?) platform. Has 
anyone an idea of whether anything beyond stereo would be feasible on XO?




-odac0 -m0d  -b128 -B2048




sr      = 44100
ksmps   = 10
nchnls  = 2

 instr 1 ; pan

aout    vco2  4615, 440, 12
kpan    linseg 0, 2, 0, 4, 1, 2, 1, 4, 0, 2, 0, 4, 1, 2, 1
a1,a2,a3,a4 pan aout, kpan, 1, 1, 1
 outs a1, a2

 endin

 instr 2 ; ambisonics (stereo, after Lazzarini)

aout    vco2  1000, 440, 12
kpan    linseg 180, 2, 180, 4, 0, 2, 0, 4, 180, 2, 180, 4, 0, 2, 0
aW,aX,aY,aZ bformenc aout, kpan, 0, 1, 1
a1,a2,a3,a4,a5,a6,a7,a8  bformdec  4, aW, aX, aY, aZ
 outs a3+a4+a5+a6, a2+a1+a8+a7

 endin





f1 0 8193 9 .25 1 0
i1 0 20
i2 22 20

e




Art Hunkins

----- Original Message ----- 
From: "Fons Adriaensen" 
To: 
Sent: Monday, July 21, 2008 11:59 AM
Subject: Re: [Cs-dev] Ambisonics Request


> On Mon, Jul 21, 2008 at 11:39:14AM -0400, Art Hunkins wrote:
>
>> Stereo ambisonic decoding in Csound never worked correctly, though I was
>> quite happy with the results of Victor's "kludge": to add four outputs 
>> each
>> of bformenc into the inputs of a stereo decode.
>
> If your source material is Ambisonic, i.e. the output of
> bformenc or any other software that generates B-format,
> or from an Ambisonic microphone, then the normal way to
> reproduce it in stereo is to send the summed B-format
> signals to a stereo decoder. That's not a 'kludge'.
> It's not normally called a 'decoder' but a virtual
> stereo microphone in that case, and you should have
> the options to set the direction the mics point at,
> their angle, and their polar pattern. There's no
> need to write an opcode for this, it's easy enough
> to code right into an instrument. Both L and R are
> just linear combinations of the B-format signals.
> So it's indeed just the same as panning, and if your
> only intent is to produce a normal stereo signal
> their is no reason to make the detour via Ambisonics.
>
> OTOH, if you only want to reproduce via headphones
> only there is a completely different way to handle
> things, and in that case it makes sense to go via
> Ambisonics. You can render Ambisonics on headphones
> by converting it to binaural, which means by calculating
> the signals that would be generated at the listeners
> ears if he/she were listening to an Ambisonic surround
> system.
>
> This is not so simple, it involves decoding the AMB
> signal and then using the HRIR 'head related impulse
> responses' by convolution.
>
> Apart from that there are techniques to make any
> synthetic sound more 'natural'. They can be used
> in Ambisonics, but are not 'Ambisonic' per se.
>
> Ciao,
>
> -- 
> FA
>
> Laboratorio di Acustica ed Elettroacustica
> Parma, Italia
>
> O tu, che porte, correndo si ?
> E guerra e morte !
>
>
>
>
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