SURROUND FIELDS

Most surround sound is recorded as a mixdown of individual tracks, panned in a mixer to produce a convincing effect. But these techniques do not record the actual conditions someone would actually hear in the field. The following technique can capture the actual sound in the field, and also reproduces it without the separation-enhancing logic usually needed with matrix surround systems.

DISCOVERY OF THE SURROUND FIELD

The page author set up the three mic design as indicated as an experiment to record a solo vocalist, and try to also capture some of the room reverberation. The soloist was about two feet from the L and R mics.

The soloist practiced the part a few times before the first take. Then we recorded the take.

The author rewound the tape to play it through the stereo monitor speakers, and started the tape playing at the beginning. Then the following conversation took place:

Author: "Would you please stop practicing? I want to hear the tape."

Soloist: "That's not me. It's the tape!"

It sounded so real that the page author didn't realize it was the tape playing. He thought it was the soloist practicing again.

The page author then continued to experiment and perfect the system over several years.

RECORDING THE SURROUND FIELD

surround field vectors The surround field mic cluster can be used either alone or with close miked musicians. Amazingly, they don't interfere with each other.

The following method is used to record a surround field"

  1. The surround field microphone cluster is usually made with three cardioid mics. I call it the "Surrfield" system.
  2. surround field vectors The surround field microphone cluster has four mics when vertical directionality is also needed. I call it the "Spheround" system.
  3. The surround field mic cluster can be used alone, or combined with close mics for soloists or a mix from a band's house mixer.
  4. When the surround field cluster is used with close mics or the mix from a band, place the cluster at least 20 feet away from the front of the band.
  5. If a live audience is to be present, the cluster should be at least 11 feet above the floor, preferably where it won't be disturbed by the audience. This also makes sure the audience does not drown out the desired sound.

The mics should be wired to a mixer as follows:

  1. surround field mic Connect the left mic to a channel strip that is panned left (or slightly in from left.
  2. Connect the right mic to a channel strip that is panned left (or slightly in from left.
  3. If a 3-mic system is used:
    1. Connect the surround mic to the adaptor. *
    2. Connect the adaptor to two channel strips. Pan one strip hard left, the other strip hard right.
  4. If a 4-mic system is used:
    1. Connect the surround zenith mic to a channel strip panned hard right.
    2. Connect the surround nadir mic to a channel strip panned hard left.
    3. Connect the surround zenith channel insert send to the left channel input of an SQ 10-40 decoder. **
    4. Connect the surround zenith channel insert return to the left back output of the SQ decoder.
    5. Connect the surround nadir channel insert send to the right channel input of the SQ decoder.
    6. Connect the surround nadir channel insert return to the right back output of the SQ decoder.

* Use the adaptor in the image above for a balanced-line mic. For the unbalanced mic, connect the mic to one channel strip, and connect its channel strip insert send to the return of another channel strip through this circuit set in the reverse position.

** The use of an SQ decoder as an encoder is covered here.

PLAYING BACK THE SURROUND FIELD

Any of the following can be used to play back the sound field:

octophonic surround Setting up the Octophonic decoder:

  1. Place the speakers as follows:
    LM F RM
    LW head RW
    LP B RP
  2. Play a mono recording.
  3. Turn Width control to maximum (CW), and the Focus and Depth controls to minimum (CCW).
  4. Turn up the W and P levels, and turn all of the others all the way down.
  5. Set the Filter control to OUT.
  6. Set the NULL switch to the NULL position (open).
  7. Adjust the balance control on the stereo for minimum sound from the speakers. Remember the control position.
  8. Set the NULL switch to the normal position (closed).
  9. Adjust the level controls so all speakers except B are at the same level. Remember these control positions.
  10. Set the FOCUS control so the W speakers are slightly quieter than the M speakers.
  11. Set the DEPTH control so the P speakers are about half the loudness of the M speakers.
  12. Turn all the level controls down except M.
  13. Turn the balance control all the way left.
  14. Adjust the WIDTH control so the RM speaker is slightly less than half the level of the LM speaker.
  15. Turn up the B control until the B level is slightly more than half the LM level. Remember this control position.
  16. Set the level controls back to the remembered positions.
  17. Set the balance control on the stereo back to the remembered position. If necessary, use the NULL switch again as in steps 5 -- 7.
  18. If the SQ decoder is used for height in addition to the octophonic decoder, adjust the level so it is audible when a high or low source is played, but not when other sources are played.
  19. The relative levels might need adjustment for different recordings.

WHY THE SURROUND FIELD MIC CLUSTER WORKS

This system is based on the relative levels and times of arrival of the signals from each of the mics. They produce the proper sounds at the ears to recreate the original sounds.

Here is a table of relative levels and delays (in microseconds) recorded on the tracks of the recording for different directions of sound sources:

Angle Volume
L
delay
L
  Volume
R
delay
R
 Volume
S
delay
S
 Direction  1st2nd3rd
0 0.8660  0.8660 0.200 ~885  Straight Ahead L RS 
15 0.793191  0.9240 0.131950    RLs
30 0.707369  0.9660 0.259951    RLS
45 0.609521  0.9910 0.383886    RLS
60 0.500639  1.0000 0.500762  Right Mic RL S 
75 0.383712  0.9910 0.609585    RSL
90 0.259737  0.9660 0.707369  Straight Right RSL
105 0.131712  0.9240 0.793127    RSl
120 0.200 ~762  0.866123 0.8660    R SL 
135 0.131886  0.793365 0.9240    SRl
150 0.259951  0.707582 0.9660    SRL
165 0.383950  0.609759 0.9910    SRL
180 0.500885  0.500885 1.0000  Straight Back Mic SL R 
195 0.609759  0.383950 0.9910    SLR
210 0.707582  0.259951 0.9660    SLR
225 0.793365  0.131886 0.9240    SLr
240 0.866123  0.200 ~762 0.8660    L SR 
255 0.9240  0.131712 0.793127    LSr
270 0.9660  0.259737 0.707369  Straight Left LSR
285 0.9910  0.383712 0.609585    LSR
300 1.0000  0.500639 0.500762  Left Mic LR S 
315 0.9910  0.609521 0.383886    LRS
330 0.9660  0.707369 0.259951    LRS
345 0.9240  0.793191 0.131950    LRs
360 0.8660  0.8660 0.200 ~885  Straight Ahead L RS 

~ Varies with the amount of room spill leaking into the mic pointing directly away from the sound.

The delays and the reduced volumes cause the ears to correctly determine the direction of sound.

In addition, reflections of sounds from room surfaces come from different directions, and activate the mics from the directions they come from. This further reinforces the perceived direction of the sound. The sound recorded sounds quite real.

WHY THE OCTOPHONIC SPEAKER ARRAY WORKS

The Octophonic array works better than the old quadraphonic systems for these reasons:

These diagrams show the relative levels of each of the speakers for 10 sound locations:

LM SOUND   F-LM 22.5° SOUND   F SOUND   F-RM 30° SOUND   RM SOUND
LM
1.0
F
.92
RM
.71
LM
.98
F
.98
RM
.83
LM
.92
F
1.0
RM
.92
LM
.79
F
.97
RM
.99
LM
.71
F
.92
RM
1.0
LW
.92
head RW
.38
LW
.83
head RW
.56
LW
.71
head RW
.71
LW
.50
head RW
.87
LW
.38
head RW
.92
LP
.71
B
.38
RP
.00
LP
.56
B
.20
RP
.20
LP
.38
B
.00
RP
.38
LP
.13
B
.26
RP
.61
LP
.00
B
.38
RP
.71
* * * * * * * * *
LW SOUND   LP SOUND   B SOUND   RP SOUND   RW SOUND
LM
.92
F
.71
RM
.38
LM
.71
F
.38
RM
.00
LM
.38
F
.00
RM
.38
LM
.00
F
.38
RM
.71
LM
.38
F
.71
RM
.92
LW
1.0
head RW
.00
LW
.92
head RW
.38
LW
.71
head RW
.71
LW
.38
head RW
.92
LW
.00
head RW
1.0
LP
.92
B
.71
RP
.38
LP
1.0
B
.92
RP
.71
LP
.92
B
1.0
RP
.92
LP
.71
B
.92
RP
1.0
LP
.38
B
.71
RP
.92

The listener is the head in the center of each diagram.

The sound is intended to come from the direction shown in amber.

The amber and white speakers make the "wall of sound."

The speakers shown in blue violet contribute less to the sound than the others.

LOCATIONS OF THE SOUND IMAGES

A listener centered in the room hears the sounds in their proper locations. These computer simulations show how a listener hears eight image locations when sitting halfway between the room center and one of the speakers.

Note: The same results occur if the listener is off-center in other directions.

Note the following:

  • Fig. 1 shows the 8 encoded locations and all speaker locations (from center).
  • Fig. 2 and Fig. 3 show the angles of the speakers with respect to the listener.
  • Sounds are heard ahead of their encoded positions in a quadraphonic array (Fig. 4).
  • Sounds are heard behind their encoded positions in an octophonic array (Fig. 5).
  • Turning the B speaker down to 70% in the octophonic array (Fig. 6) corrects the octophonic images for listeners behind the center of the room.
  • Fig. 7 shows dodecaphonic speaker angles with respect to the listener. Each speaker in a pair with the same name (with a "d") carries the same signal. Octophonic signals are used.
  • Sounds are heard near their encoded positions in a dodecaphonic array (Fig. 8). The F, W, and B speakers are turned down to 70% of the levels of the M and P speakers.
  • Sounds are heard near their encoded positions with the F, W, and B speakers set at 30% of the M and P levels in the octophonic array (Fig. 9).
REGULAR MATRIX ENCODING
AND SPEAKER ANGLES
  QUADRAPHONIC
LISTENER SPEAKER ANGLES
  OCTOPHONIC
LISTENER SPEAKER ANGLES
LM
-45°
Fd
-27°
F
 0°
Fd
 27°
RM
 45°
LM
-34°
 
 
 
 
 
 
RM
 34°
LM
-34°
 
 
F
 0°
 
 
RM
 34°
LWd
-63°
 
 
Fig
1
 
 
RWd
 63°
 
 
 
 
Fig
2
 
 
 
 
 
 
 
 
Fig
3
 
 
 
 
LW
-90°
 
 
head  
 
RW
 90°
 
 
 
 
 
 
 
 
 
 
LW
-63°
 
 
 
 
 
 
RW
 63°
LWd
-117°
 
 
 
 
 
 
RWd
 117°
 
 
 
 
head  
 
 
 
 
 
 
 
head  
 
 
 
LP
-135°
Bd
-153°
B
 180°
Bd
 153°
RP
 135°
LP
-117°
 
 
 
 
 
 
RP
 117°
LP
-117°
 
 
B
 180°
 
 
RP
 117°
* * * * *
EQUAL AMPLITUDE
QUADRAPHONIC IMAGE ANGLES
  EQUAL AMPLITUDE
OCTOPHONIC IMAGE ANGLES
  B SPEAKER 70% OF OTHERS
OCTOPHONIC IMAGE ANGLES
LM
-52°
 
 
F
 0°
 
 
RM
 52°
LM
-51°
 
 
F
 0°
 
 
RM
 51°
LM
-45°
 
 
F
 0°
 
 
RM
 45°
 
 
 
 
Fig
4
 
 
 
 
 
 
 
 
Fig
5
 
 
 
 
 
 
 
 
Fig
6
 
 
 
 
LW
-82°
 
 
 
 
 
 
RW
 82°
LW
-108°
 
 
 
 
 
 
RW
 108°
LW
-92°
 
 
 
 
 
 
RW
 92°
 
 
 
 
head  
 
 
 
 
 
 
 
head  
 
 
 
 
 
 
 
head  
 
 
 
LP
-128°
 
 
B
 180°
 
 
RP
 128°
LP
-148°
 
 
B
 180°
 
 
RP
 148°
LP
-135°
 
 
B
 180°
 
 
RP
 135°
* * * * *
DODECAPHONIC
LISTENER SPEAKER ANGLES
  F W B SPEAKERS AT 70%
DODECAPHONIC IMAGE ANGLES
  F W B SPEAKERS AT 30%
OCTOPHONIC IMAGE ANGLES
LM
-34°
Fd
-18°
 
 
Fd
 18°
RM
 34°
LM
-46°
 
 
F
 0°
 
 
RM
 46°
LM
-52°
 
 
F
 0°
 
 
RM
 52°
LWd
-45°
 
 
Fig
7
 
 
RWd
 45°
 
 
 
 
Fig
8
 
 
 
 
 
 
 
 
Fig
9
 
 
 
 
 
 
 
 
 
 
 
 
 
 
LW
-89°
 
 
 
 
 
 
RW
 89°
LW
-96°
 
 
 
 
 
 
RW
 96°
LWd
-90°
 
 
head  
 
RWd
 90°
 
 
 
 
head  
 
 
 
 
 
 
 
head  
 
 
 
LP
-117°
Bd
-135°
 
 
Bd
 135°
RP
 117°
LP
-131°
 
 
B
 180°
 
 
RP
 131°
LP
-139°
 
 
B
 180°
 
 
RP
 139°

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