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Signal Modifiers: Panning and Spatialization

vbaplsinit, vbap4, vbap8, vbap16, vbap4move, vbap8move, vbap16move, vbapz, vbapzmove

                                                 vbaplsinit    idim, ilsnum, idir1, idir2,... 

ar1, ar2, ar3, ar4                               vbap4         asig, iazim, ielev, ispread
 
ar1, ar2, ar3, ar4, ar5, ar6, ar7, ar8           vbap8         asig, iazim, ielev, ispread
 
ar1, ar2, ar3, ar4, ar5, ar6, ar7, ar8,          vbap16        asig, iazim, ielev, ispread
ar9, ar10, ar11, ar12, ar13, ar14, ar15, ar16
                   
ar1, ar2, ar3, ar4                               vbap4move     asig, ispread, ifldnum, ifld1, ifld2, ...
 
ar1, ar2, ar3, ar4, ar5, ar6, ar7, ar8           vbap8move     asig, ispread, ifldnum, ifld1, ifld2, ...
 
ar1, ar2, ar3, ar4, ar5, ar6, ar7, ar8,          vbap16move    asig, ispread, ifldnum, ifld1, ifld2, ...
ar9, ar10, ar11, ar12, ar13, ar14, ar15, ar16
 
                                                 vbapz         inumchnls, istartndx, asig, iazim, ielev, ispread
                                                 vbapzmove     inumchnls, istartndx, ispread, ifldnum, ifld1, ifld2,...



Description

Distribute an audio signal among 2 to 16 channels or write it to a ZAK array, all with localization control.

Initialization

idim – dimensionality of loudspeaker array. Either 2 or 3.

ilsnum – number of loudspeakers. In two dimensions, the number can vary from 2 to 16. In three dimensions, the number can vary from 3 and 16.

idir1, idir2, etc. – directions of loudspeakers. Number of directions must be less than or equal to 16. In two-dimensional loudspeaker positioning, idirn is the azimuth angle respective to nth channel. In three-dimensional loudspeaker positioning, fields are the azimuth and elevation angles of each loudspeaker consequently (azi1, ele1, azi2, ele2, etc.).

iazim – azimuth angle of the virtual source

ielev – elevation angle of the virtual source

ispread – spreading of the virtual source (range 0 - 100). If value is zero, conventional amplitude panning is used. When ispread is increased, the number of loudspeakers used in panning increases. If value is 100, the sound is applied to all loudspeakers.

ifldnum – number of fields (absolute value must be 2 or larger). If ifldnum is positive, the virtual source movement is a polyline specified by given directions. Each transition is performed in an equal time interval. If ifldnum is negative, specified angular velocities are applied to the virtual source during specified relative time intervals (see below).

ifld1, ifld2, etc. – azimuth angles or angular velocities, and relative durations of movement phases (see below).

inumchnls – number of channels to write to the ZA array. Must be in the range 2 - 256.

istartndx – first index or position in the ZA array to use

Performance

asig – audio signal to be panned

vbap4, vbap8, and vbap16 take an input signal, asig, and distribute it among 2 to 32 outputs, according to the controls iazim and ielev, and the configured loudspeaker placement. If idim = 2, ielev is set to zero. The distribution is performed using Vector Base Amplitude Panning (VBAP - See reference). VBAP distributes the signal using loudspeaker data configured with vbaplsinit. The signal is applied to, at most, two loudspeakers in 2-D loudspeaker configurations, and three loudspeakers in 3-D loudspeaker configurations. If the virtual source is panned outside the region spanned by loudspeakers, the nearest loudspeakers are used in panning.

vbap4move, vbap8move, and vbap16move allow the use of moving virtual sources. If ifldnum is positive, the fields represent directions of virtual sources and equal times, iazi1, [iele1,] iazi2, [iele2,], etc. The position of the virtual source is interpolated between directions starting from the first direction and ending at the last. Each interval is interpolated in time that is fraction total_time / number_of_intervals of the duration of the sound event.

If ifldnum is negative, the fields represent angular velocities and equal times. The first field is, however, the starting direction, iazi1, [iele1,] iazi_vel1, [iele_vel1,] iazi_vel2, [iele_vel2,] .... Each velocity is applied to the note that is fraction total_time / number_of_velocities of the duration of the sound event. If the elevation of the virtual source becomes greater than 90 degrees or less than 0 degrees, the polarity of angular velocity is changed. Thus the elevational angular velocity produces a virtual source that moves up and down between 0 and 90 degrees.

The opcodes vbapz and vbapzmove are the multiple channel analogs of the above opcodes, working on inumchnls and using a ZAK array for output.

Example

2-D panning example with stationary virtual sources:

  sr      =          4100
  kr      =           441
  ksmps   =           100
  nchnls  =             4
  vbaplsinit         2, 6,  0, 45, 90, 135, 200, 245, 290, 315 

          instr 1	           
  asig    oscil      20000, 440, 1                    
  a1,a2,a3,a4,a5,a6,a7,a8   vbap8  asig, p4, 0, 20 ;p4 = azimuth
	
  ;render twice with alternate outq statements
  ;  to obtain two 4 channel .wav files:

          outq       a1,a2,a3,a4
  ;       outq       a5,a6,a7,a8
          endin

Reference

Ville Pulkki: "Virtual Sound Source Positioning Using Vector Base Amplitude Panning"
Journal of the Audio Engineering Society,
1997 June, Vol. 45/6, p. 456.

Authors

Ville Pulkki
Sibelius Academy Computer Music Studio
Laboratory of Acoustics and Audio Signal Processing
Helsinki University of Technology
Helsinki, Finland
May, 2000 (New in Csound Version 4.16)

John ffitch (vbapz, vbabzmove)
University of Bath/Codemist Ltd.
Bath, UK
May, 2000 (New in Csound Version 4.16)


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Signal Modifiers: Panning and Spatialization