The Alternative Csound Reference Manual
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# spdist

spdist -- Calculates distance values from xy coordinates.

## Description

spdist uses the same xy data as space, also either from a text file using Gen28 or from x and y arguments given to the unit directly. The purpose of this unit is to make available the values for distance that are calculated from the xy coordinates.

In the case of space, the xy values are used to determine a distance which is used to attenuate the signal and prepare it for use in spsend. But it is also useful to have these values for distance available to scale the frequency of the signal before it is sent to the space unit.

## Syntax

k1 spdist ifn, ktime, kx, ky

## Initialization

ifn -- number of the stored function created using Gen28. This function generator reads a text file which contains sets of three values representing the xy coordinates and a time-tag for when the signal should be placed at that location. The file should look like:

0 -1 1
1 1 1
2 4 4
2.1 -4 -4
3 10 -10
5 -40 0

If that file were named "move" then the Gen28 call in the score would like:

f1 0 0 28 "move"

Gen28 takes 0 as the size and automatically allocates memory. It creates values to 10 milliseconds of resolution. So in this case there will be 500 values created by interpolating X1 to X2 to X3 and so on, and Y1 to Y2 to Y3 and so on, over the appropriate number of values that are stored in the function table. In the above example, the sound will begin in the left front, over 1 second it will move to the right front, over another second it move further into the distance but still in the left front, then in just 1/10th of a second it moves to the left rear, a bit distant. Finally over the last .9 seconds the sound will move to the right rear, moderately distant, and it comes to rest between the two left channels (due west!), quite distant. Since the values in the table are accessed through the use of a time-pointer in the space unit, the actual timing can be made to follow the file's timing exactly or it can be made to go faster or slower through the same trajectory. If you have access to the GUI that allows one to draw and edit the files, there is no need to create the text files manually. But as long as the file is ASCII and in the format shown above, it doesn't matter how it is made!

IMPORTANT: If ifn is 0 then space will take its values for the xy coordinates from kx and ky.

## Performance

The configuration of the xy coordinates in space places the signal in the following way:

- a1 is -1, 1

- a2 is 1, 1

- a3 is -1, -1

- a4 is 1, -1

This assumes a loudspeaker set up as a1 is left front, a2 is right front, a3 is left back, a4 is right back. Values greater than 1 will result in sounds being attenuated, as if in the distance. space considers the speakers to be at a distance of 1; smaller values of xy can be used, but space will not amplify the signal in this case. It will, however balance the signal so that it can sound as if it were within the 4 speaker space. x=0, y=1, will place the signal equally balanced between left and right front channels, x=y=0 will place the signal equally in all 4 channels, and so on. Although there must be 4 output signals from space, it can be used in a 2 channel orchestra. If the xy's are kept so that Y>=1, it should work well to do panning and fixed localization in a stereo field.

ktime -- index into the table containing the xy coordinates. If used like:

ktime line 0, 5, 5
a1, a2, a3, a4 space asig, 1, ktime, ...

with the file "move" described above, the speed of the signal's movement will be exactly as described in that file. However:

ktime line 0, 10, 5

the signal will move at half the speed specified. Or in the case of:

ktime line 5, 15, 0

the signal will move in the reverse direction as specified and 3 times slower! Finally:

ktime line 2, 10, 3

will cause the signal to move only from the place specified in line 3 of the text file to the place specified in line 5 of the text file, and it will take 10 seconds to do it.

kx, ky -- when ifn is 0, space and spdist will use these values as the XY coordinates to localize the signal.

## Examples

    instr 1
      asig    ;some audio signal
      ktime              line  0, p3, p10
      a1, a2, a3, a4     space asig,1, ktime, .1
      ar1, ar2, ar3, ar4 spsend

      ga1 = ga1+ar1
      ga2 = ga2+ar2
      ga3 = ga3+ar3
      ga4 = ga4+ar4

                         outq a1, a2, a3, a4
    endin

    instr 99 ; reverb instrument

      a1 reverb2 ga1, 2.5, .5
      a2 reverb2 ga2, 2.5, .5
      a3 reverb2 ga3, 2.5, .5
      a4 reverb2 ga4, 2.5, .5

         outq a1, a2, a3, a4
      ga1=0
      ga2=0
      ga3=0
      ga4=0

In the above example, the signal, asig, is moved according to the data in Function #1 indexed by ktime. space sends the appropriate amount of the signal internally to spsend. The outputs of the spsend are added to global accumulators in a common Csound style and the global signals are used as inputs to the reverb units in a separate instrument.

space can useful for quad and stereo panning as well as fixed placed of sounds anywhere between two loudspeakers. Below is an example of the fixed placement of sounds in a stereo field using xy values from the score instead of a function table.

    instr 1
      ...
      a1, a2, a3, a4     space asig, 0, 0, .1, p4, p5
      ar1, ar2, ar3, ar4 spsend

      ga1=ga1+ar1
      ga2=ga2+ar2
                         outs  a1, a2
    endin

    instr 99 ; reverb....
      ....
    endin

A few notes: p4 and p5 are the X and Y values

      ;place the sound in the left speaker and near
        i1 0 1 -1 1
      ;place the sound in the right speaker and far
        i1 1 1 45 45
      ;place the sound equally between left and right and in the middle ground distance
        i1 2 1 0 12
    e

The next example shows a simple intuitive use of the distance values returned by spdist to simulate Doppler shift.

      ktime              line   0, p3, 10
      kdist              spdist 1, ktime
      kfreq = (ifreq * 340) / (340 + kdist)
      asig               oscili iamp, kfreq, 1

      a1, a2, a3, a4     space  asig, 1, ktime, .1
      ar1, ar2, ar3, ar4 spsend

The same function and time values are used for both spdist and space. This insures that the distance values used internally in the space unit will be the same as those returned by spdist to give the impression of a Doppler shift!

## See Also

space, spsend

## Credits

Author: Richard Karpen
Seattle, WA USA
1998

New in Csound version 3.48

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