MIXING MATRIX SURROUND SOUND

WITH AN ORDINARY 4-SUBGROUP MIXER


UniQuad HOW THIS WORKS:

This method of mixing matrixed surround sound uses the pan positions and phases used in real surround sound systems. This list and the diagram show how the Regular Matrix (RM) and Dolby Surround (DS) handle the signals:

The Sansui QS, Dynaquad, and Electro Voice systems were the same as Regular Matrix (RM).

Other matrix encoding systems exist, but they are no longer used. They include:

Use Advanced Mixing Matrix Surround Sound to encode these other matrix systems.


WHAT YOU NEED:

  1. One 4 SUBGROUP (or 2+2) or larger audio mixer with the following
  2. Other parts:
  3. Depending on your setup, you might need these:
  4. Soldering ability and knowledge of balanced line connections (or friend so equipped).
  5. An optional acroperiphonic method of placing a sound source overhead (or in the midst of the audience, depending on the speaker height) can be implemented with the following additional equipment:

CHOOSING THE SUBS, SENDS, AND RETURNS

  1. First, determine whether your mixer has balanced or unbalanced SUB subgroup outputs. Choose a stereo pair from your available SUB OUTs. It must not be the subgroup used for the MAIN output. This page will call it your SUB or SUB OUT. Label that pair of groups as ENCODER.
  2. If the subgroup for your final output is not the MAIN group, refer to that subgroup wherever the text below refers to the MAIN group.
  3. Select your (preferably balanced-line) stereo input you plan to use. It may be an AUX RETURN, a stereo channel input, or a pair of panable mono inputs. This page will call it your ENCODER RETURN. Label it ENCODER RETURN.
  4. If you are using SUB INSERTs for the encoder, call the INSERT or SEND and RETURN jacks your ENCODER INSERT jacks.
  5. If you want acroperiphonic sound, select an after-fader AUX SEND (or EFFECTS OUT). This page will call it your AUX SEND. Label it ACRO SEND.
  6. For acroperiphonic capability, select a mono panable input channel or mono-capable AUX RETURN. For the Special Mackies, this input must be SUB assignable. This page will call it your ACRO RETURN. Label it so.
  7. Note: If you chose channel inputs for either of the returns, setting the return level uses the channel fader plus any trim controls available.

CONSTRUCTING THE CABLES

The sample illustrations show 1/4 inch phone plugs. Substitute the type of connector you are really using.

Patch cord A. Choose the selection that best fits your mixer:

  1. Fully balanced SUB OUT and ENCODER RETURN jacks
  2. Impedance balanced SUB OUT, fully balanced ENCODER RETURN
  3. Unbalanced SUB OUT, fully balanced ENCODER RETURN
  4. ENCODER INSERT jacks
  5. Unbalanced ENCODER RETURN
  6. You had hum problems using one of the balanced methods.
  7. You have built a UniQuad Phlazex. Set it for Encode Surround Right-Biased

Patch cord B. If you want the acroperiphonic feature, find your ACRO RETURN type:

  1. Mono
  2. Tip-Ring-Sleeve stereo
  3. Stereo on two jacks

Patch cord C. If you want the acroperiphonic feature, find your AUX SEND type:

  1. Mono
  2. Tip-Ring-Sleeve stereo
  3. Stereo on two jacks

surround sound mixer connections CONNECTING THE CABLES TO THE MIXER


FLIPPING BETWEEN GROUPS

To FLIP the channel assign selection between groups is necessary to select either front or back encoding positions. This procedure assumes that either the MAIN group or the SUB group is already assigned. The FLIP operation consists of deselecting one group, and simultaneously assigning the other. This is easy to do with most mixers:

  1. On mixers with separate MAIN and SUB channel assign buttons, press both buttons at exactly the same time. One will latch as the other unlatches. The Mackie SR 24.4 has this type of group assign.
  2. On mixers with ALT 3-4 GROUP channel assign buttons, pressing the single button automatically disconnects one group as it assigns the other. The Samson PL2404 has this type of assign.
  3. If you accidentally assign both groups at the same time, the sound image will shift to the wrong position.
  4. If you accidentally disconnect both groups at the same time, the source will disappear from the mix.

SETTING UP THE CONTROLS

  1. Assign the ENCODER RETURN and the ACRO RETURN to the MAIN GROUP (Note: On the Special Mackies, the ACRO RETURN must be assigned to the SUB for it to work right).
  2. If a stereo input is used for the ENCODER RETURNs, center the BALANCE control.
  3. If two mono channels are used for the ENCODER RETURNs, set the left one's PAN control all the way left, and the right one's PAN control all the way right.
  4. Center the BALANCE or PAN control of the ACRO RETURN (if used).
  5. If you can, set the SUB OUT to unity gain.
  6. If you can, set the ENCODER RETURN to unity gain (This is also the SUB OUT fader if encoder inserts are used).
  7. Connect a sound source to one of the channel inputs.
  8. Turn your ACRO SEND all the way down.
  9. Mute (or fade down) the ACRO RETURN.
  10. Assign the source's channel input to the MAIN group and adjust the TRIM, channel fader, and MAIN fader for good sound level.
  11. Turn the PAN control of the sound source all the way LEFT.
  12. FLIP (see procedure above) the source's channel from the MAIN group to the encoder's SUB group. The sound level should not change. If it does change, adjust the SUB OUT fader pair and the ENCODER RETURN (preferably one not calibrated for unity gain). Always set both SUB OUT faders to the same setting.
  13. FLIP (see procedure above) back and forth between the MAIN and the SUB. The level should not change as you switch the assignment.
  14. Repeat the above test with the source's PAN control all the way RIGHT.
  15. Mark the settings of the SUB OUT and ENCODER RETURN so you can accurately set them again.

If you are not using the digital delay for acroperiphonic sounds, you are done with the adjustments. Otherwise, continue:

  1. Set the digital delay for a 15 millisecond delay.
  2. Assign the source's channel to the SUB (Note: For acroperiphonics to work right on the Special Mackies, use MAIN instead).
  3. Mute (or fade down) the ACRO RETURN, and notice the sound level.
  4. Set the source's ACRO SEND to unity gain.
  5. Mute (or fade down) the SUB OUT and open the ACRO RETURN. Adjust the controls of the digital delay and the ACRO RETURN for the same level noticed earlier. (On the Special Mackies, this is impossible to do. Instead, try to adjust the ACRO RETURN so it gives the same amount of sound as the MAIN output from the channel.)
  6. Alternately open either the SUB OUT or ACRO RETURN (with the other closed) to get the same sound level from both.
  7. Mark the settings on the digital delay and ACRO RETURN controls so you can accurately set them again.

USING THE ENCODER

Encoding around the periphery of the surround area:

  1. Set SUB OUT and ENCODER RETURN to their marked settings.
  2. If used, set the digital delay and ACRO RETURN to their marked settings.
  3. Each input channel can be positioned independently in the surround image.
  4. To place or pan a channel in the front half of the surround image, turn down the ACRO SEND and select only the MAIN group. Use the PAN control to position the source laterally. (NOTE: at the extreme ends of the PAN control, the source will curve around to the straight left or straight right position.
  5. To place or pan a channel in the rear half of the surround image, turn down the ACRO SEND and select only the encoder's SUB group. Use the PAN control to position the source laterally. Again, the source will curve around at the ends of the PAN control.
  6. To make a source jump from the front to the back half, FLIP (see procedure above) it from the MAIN group to the SUB group.
  7. To make a source jump from the back to the front half, FLIP it from the SUB group to the MAIN group.
  8. To make a source pan from the front to the back half, turn the PAN control all the way left (or right). Then quickly FLIP from the MAIN group to the SUB group. Then pan the source to where it will end up.
  9. To make a source pan from the back to the front half, turn the PAN control all the way left (or right). Then quickly FLIP from the SUB group to the MAIN group. Then pan the source to where it will end up.
  10. The previous two procedures can be combined to make a source circle the audience.
  11. Notice that when you SOLO a channel in AFL, it always appears in the front half in the SOLO output, no matter where it is actually encoded. This is a characteristic of most SOLO systems, not a failure.

Pan diagram To place a source overhead (assuming the surround speakers are higher than ear level):

  1. Select only the SUB group.
  2. Center the PAN control.
  3. Set the source's ACRO SEND to unity gain.
  4. It is necessary to use a lower channel FADER setting to maintain the same overall sound level.

On the Special Mackies, to place a source overhead:

  1. Select the MAIN group.
  2. Center the PAN control.
  3. Set the source's AUX SEND to unity gain.
  4. It is necessary to use a lower channel FADER setting to maintain the same overall sound level.

Off center acroperiphonic sources are hard to locate by ear, but can be created by use of the PAN, FADER, and AUX SEND controls on the channel:

NOTE: On the Special Mackies, interchange the words "back" and "front" in this list:

At all times, the FADER can be used by itself to fade the source down to nothing.


Here is a sample mixer with settings used for various pan positions:

The label on the mixer I designed this diagram from says LEV (level) instead of FADER, possibly because it has rotary faders. I preserved it in the diagram.


Links:

  1. QUADRAPHONIC AND SURROUND INDEX PAGE
  2. Advanced Mixing Matrix Surround Sound
  3. Stereo and surround sound
  4. Albums and soundtracks I recorded
  5. HOME