#Chapter 07: Mix Buses, Sends-on-Faders & Matrices

The Behringer X32 and Midas M32 internal architecture includes 25 time-aligned mix buses: 16 configurable Mix Buses, 6 Matrix Buses, and the Main Left, Right, and Center/Mono buses.

This chapter details mix bus tap configurations, the Sends-on-Faders workflow, stage monitoring (wedges vs. in-ears), audio subgroups versus DCAs, parallel drum processing, and matrix system tuning.

#1. The 16 Mix Buses Architecture

The 16 Mix Buses serve multiple roles across live and studio environments:

• Auxiliary Sends: Stage floor wedges, in-ear monitors (IEMs), headphone mixes.
• Effects Sends: Feeding internal reverb, delay, and modulation processors (typically Buses 13–16).
• Audio Subgroups: Grouping drums, backing vocals, or horns for collective bus processing.

#Mix Bus Processing Capabilities:

Every one of the 16 mix buses features its own complete processing chain:

1. 6-Band Fully Parametric EQ: Bands 1 and 6 can switch between Low/High Cut, Shelving, or Parametric peaking.
2. Dynamics Processor: Complete compressor/limiter with RMS/Peak detection and make-up gain.
3. Insert Slot: Can insert any virtual rack effect or external hardware unit.
4. Bus Delay: Adjustable up to 500 ms for acoustic time-alignment.
5. Stereo Linking: Buses can be linked in adjacent odd/even pairs (1+2, 3+4, 5+6, etc.) for stereo in-ear monitoring.

#2. The Sends-on-Faders (SoF) Workflow

Mixing stage monitors and effects sends using small rotary knobs can be slow and inaccurate. The Sends on Faders mode transforms the motorized faders into physical send controls.

Press SENDS ON FADER (it flashes red), then either:

#To Exit Sends on Faders:

Press the flashing red SENDS ON FADER button again. The console faders instantly return to their normal house mix positions.

#3. Floor Monitors (Wedges) vs. In-Ear Monitors (IEMs)

#A. Floor Monitors (Stage Wedges):

• Mandatory Setting: Configure buses feeding floor wedges to PRE-FADER (or Post-EQ).
• Why Pre-Fader is Mandatory: If a stage wedge is post-fader, every time the FOH engineer pushes or pulls a fader in the house, the volume in the musician's wedge changes. If the FOH engineer pulls down a vocalist during a quiet speech, the singer can no longer hear themselves. If the FOH engineer pushes a guitar solo, the wedge can instantly feed back into the microphones.
• Feedback Ringing: Insert a Dual TruEQ or use the bus's onboard 6-band PEQ with narrow notch filters (Q = 8.0) to cut stage feedback rings identified on the RTA.

#B. In-Ear Monitors (IEMs):

• Stereo Bus Linking: Link adjacent buses (e.g., Bus 1+2 for Lead Singer IEM, Bus 3+4 for Drummer IEM).
• Pan Positioning: Panning individual instruments in the performer's ears creates spatial separation, lowering the required overall volume and reducing ear fatigue.
• Reverb in In-Ears: Musicians love vocal reverb in their ears. Route the stereo returns of FX 1 (Reverb) to the musician's IEM bus using Sends on Faders.
• Hearing Protection Limiting: Always engage the bus dynamics compressor in Limiter mode (Ratio: 100:1, Attack: 0 ms, Fast Release) on every IEM bus. Set the threshold so it never clamps down during normal singing, but will instantly catch dropped microphones, guitar unplug pops, or accidental digital spikes before they damage the musician's hearing!

#4. Audio Subgroups vs. DCAs

Many engineers confuse Subgroups and DCAs. While both allow controlling multiple channels with a single fader, they work entirely differently:

#Setting Up an Audio Subgroup:

1. Select the channels you wish to group (e.g., Channels 1–8: Drums).
2. On Channel → Main, unassign them from STEREO LR. (They will no longer feed the house directly).
3. Route the channels to Bus 1–2 with send level set to 0 dB (Unity) and bus tap set to Subgroup.
4. Link Bus 1 and Bus 2 as a stereo pair.
5. Select Bus 1–2, route it to STEREO LR, and raise its master fader to 0 dB.
6. You now have complete drum bus processing: apply EQ, insert a bus compressor, and control the entire drum kit with Bus Faders 1–2.

#5. Parallel Drum Smash (New York Compression)

Parallel compression blends an uncompressed, dynamic drum kit with an extremely smashed, aggressively compressed duplicate:

Result: The dry drums preserve transient snap and stick attack, while the parallel crushed bus adds massive room tone, body, and sustain without muddying the mix.

#6. The 6 Matrix Mixes: "A Mix of Mixes"

A Matrix mixer does not receive inputs from individual channels. Instead, it takes inputs from Mix Buses 1–16, Main Left/Right, and Mono/Center:

#Why Use Matrices for PA System Distribution?

Feeding your PA amplifiers or active speakers directly from the Main LR fader leaves you vulnerable: if someone bumps the master fader, speaker tuning and delays are disturbed. By feeding PA zones through Matrices, your Main LR fader mixes the show, while Matrices manage speaker processing.

#Matrix Processing Features:

• 6-Band Parametric EQ: Dedicated room tuning per speaker zone.
• Limiter: Protects amplifiers and drivers from over-excursion.
• Output Delay (0 to 500 ms): Critical for distance time-alignment.

#Typical Matrix Distribution Setup:

#Time-Aligning Delay Speakers:

Sound travels through air at approximately 1.13 feet per millisecond (0.343 meters per millisecond) at 20°C (68°F).

• Example: If your Balcony Delay speakers are 50 feet (15.2 meters) from the main stage PA: $$\text{Delay} = \frac{50\text{ feet}}{1.13\text{ ft/ms}} \approx 44.2\text{ ms}$$
• Enter 44.2 ms on Matrix 4's delay line. The sound from the main PA and the delay speakers will arrive at the listener's ears simultaneously, eliminating echo and comb filtering.

#7. Main Stereo Bus & Aux-Fed Subwoofers

#Option A: Standard Stereo Main LR (Subwoofers on Crossover)

Main L/R feeds a system crossover or sub-satellite PA. All console channels feed the subwoofers equally based on their low-end content.

#Option B: Aux-Fed Subwoofers (Subwoofers on Mono/Center Bus)

Feed subwoofers exclusively from the console's Mono / Center bus:

1. Patch the physical subwoofer amplifier output to Out 14 (Source: Mono / Center, Tap: Post-Fader).
2. In the console, assign only instruments with real sub-bass content to the Mono bus:
   • Kick Drum: MONO ON
   • Bass Guitar: MONO ON
   • Synth Bass / Keyboards: MONO ON
   • Floor Tom: MONO ON
   • All Vocals, Acoustic Guitars, Cymbals, and Speech mics: MONO OFF
3. Benefit: Vocal plosives, microphone handling noise, and stage foot-thumps can never trigger the subwoofers, resulting in an exceptionally clean, punchy, and transparent low-end mix!