MROOM

timeset(timepoint, x-location, y-location)

MOVE does a better job of room-simulation with a moving source, although it is more computationally expensive.

Here's more description from older documentation of the disk-based cmix "sroom" and "mroom" instruments:

These room simulation routines will add reverberation and "roominess" to BSD-type soundfiles (integer or floating point) that are processed through them. delay lines from the source to the listener. SROOM will do essentially the same thing but is a little fancier -- the room model is rectangular, delay paths are based on "ideal" reflections from the walls, the `listener' has an exandable head, and reverberation is added to the delay lines to simulate diffusion from reflections of reflections. MROOM will create the same room model that SROOM will and pass a moving source through it.

SROOM will calculate the delay paths from the walls of a rectangular room to two points representing the corners of an "inner" or listening room. The room is set up on a Cartesian coordinate system (x-y plane) with the center of the inner room's front wall positioned at the origin (0,0).

The arguments 'insk', 'outsk', 'dur' and 'amp' represent the time to skip on the input file before beginning processing, the time to skip on the output file before writing the processed output, the duration of the input file to process, and an amplitude multiplier that will be applied to the input signal.

The variable 'Xroom' is the position along the x-axis where the right-hand wall should appear. SROOM will then create the left-hand wall at -xroom, so this value represents 1/2 the room's width (in feet). 'Yroom' is the position along the y-axis where the front wall will be drawn. The rear wall will be positioned at -yroom. 'Yroom' represents 1/2 the rooms height (also in feet).

The variables 'xsrc' and 'ysrc' are the x and y coordinates of the sound source. 'Rvbtime' is the amount of time (in seconds) it takes for the reverb comb filters to decay to .001 of their original value. Values greater than 1.0 - 1.5 tend to sound "metallic"; the frequency response of the reverb combs becomes clearly audible. '%rflct' is the percentage of sound reflected by the walls. A '%rflct' value of 100 will mean that the walls will not absorb any of the incident sound. The only attenuation in the delay paths will be due to the distance travelled from the source to the listener (-6 db for each doubling of distance). 'Xinner' is the width of the inner (or listening) room. The value represents 1/2 the true width of the inner room (in feet). 'Chan' is an optional argument to specify which channel of the currently opened input file to process through the room. The default is channel 0. Note that only one channel at a time may be processed through these rooms.

MROOM is nearly identical to SROOM. The BIG DIFFERENCE is that MROOM allows a sound to travel through the room along a defined trajectory. The sound source remains at (xsrc,ysrc) in SROOM. Consequently, the xsrc and ysrc arguments are missing from MROOM. The sound source's trajectory is defined by calls to timeset() prior to the call to MROOM. MROOM will calculate the doppler shift for the source as it moves relative to the listening room and the walls -- just like the real world! The amount of frequency shift from the doppler effect for sources moving directly towards or away from a listener (or a wall) can be calculated by:

F(new) = (c/(c + SV)) * F(old)
where c = speed of sound (1086 ft/sec); F(old) is the original source frequency; SV = source velocity (ft/sec); and F(new) is the resultant doppler-shifted frequency.

Very fast source velocities may generate some quantization noise if the position of the sound source is not updated frequently enough. In addition to the optional channel argument , MROOM has another optional argument that specifies the number of times/second to update the source position. The default value is 100. Values greater than this will cause MROOM to execute proportionally slower. Note also that to specify the 'quant', 'chan' must also be explicity written.

timeset is used to define the trajectory that the sound source travelling through MROOM will follow. Calls to timeset should precede the call to MROOM for which the curve is being defined. The arguments are very simple: time is the time (from the beginning of room processing) that the source should be at the coordinate (xval,yval). MROOM will move the source along straight lines connecting the points defined by the timeset calls.

Example of timeset:

          timeset(0, 17, 19)
          timeset(17, -10, 15)
          timeset(29, -11, -7)
          timeset(49, -20, -14)
          timeset(57, -19, -37)
          timeset(77, 14, -5)
          MROOM(14, 0.7, 77, 1, 21, 49, .9, 50, .5)

The calls to timeset before the call to MROOM specify a tra- jectory for the sound source through the room that looks approximately like this (each 'X' represents a timeset call):

                                 |+49
                                 |
                                 |
                                 |
                                 |
                                 |
                                 |
                     _X-----<----|-<------<------<----X  <--Start Here
                    /            |
     ______________|_____________|_____________________________
     -21         __X             |                  X       +21
            ____/                |           ______/
         __/                     |      ____/
        X                        |_____/
        |                  ______/
        |          _______/      |
        |   ______/              |
        |__/                     |
        X                        |
                                 |-49

Both MROOM and SROOM can use setline to draw an amplitude modification curve while mixing. If no call to setline is made there is no modification done. The syntax for the call is identical to that used in MIX.

MROOM is somewhat slow. In MROOM speeds faster than 10-20 ft/sec (depending on the frequency of the source) will prob- ably have to have higher quantization rates in MROOM to avoid distortion. MROOM runs with a default quantization rate of 100, higher rates may slow it down considerably.

/* MROOM - room simulation with moving source

   First call timeset at least twice to set trajectory of moving
   sound source:
      p0     time
      p1     x location
      p2     y location

   Then call MROOM:
      p0     output start time
      p1     input start time
      p2     input duration
      p3     amplitude multiplier
      p4     distance from middle of room to right wall (i.e., 1/2 of width)
      p5     distance from middle of room to front wall (i.e., 1/2 of depth)
      p6     reverb time (in seconds)
      p7     reflectivity (0 - 100; the higher, the more reflective)
      p8     "inner room" width (try 8)
      p9     input channel number   [optional]
      p10    control rate for trajectory   [optional]
*/

rtsetparams(44100, 2)
load("MROOM")

rtinput("/tmp/1stmove.snd")

writeit = 0
if (writeit) {
   set_option("clobber_on", "audio_off")
   rtoutput("MROOM1.snd", "sun", "float")
}

outskip = 0
inskip = 13
dur = 9
amp = 0.35
xdim = 30
ydim = 80
rvbtime = 1.0
reflect = 90.0
innerwidth = 8.0
inchan = 0
quant = 2000

timeset(0,     0-xdim, 0-ydim)
timeset(dur/2, xdim/8, ydim/8)
timeset(dur,   xdim,   ydim)

setline(0,0, dur/8,1, dur-.5,1, dur,0)

MROOM(outskip, inskip, dur, amp,
      xdim, ydim, rvbtime, reflect, innerwidth, inchan, quant)