Advanced Console Routing & Summing Physic
1. The Matrix: The Command Center of Signal Flow A Matrix is a "mixer within a mixer." While an Aux bus sums input channels, a Matrix sums Busses (Groups, Mains, and Auxes). In a professional system, the Matrix is the final point of control for the PA. We use it to create unique feeds for Mains, Subs, Front-Fills, and Delays. This allows for "System EQ" (PA tuning) to be separate from "Mix EQ."
2. Nodal Processing: The Point of Extraction Modern FPGA-based consoles offer Nodal Processing. Historically, an Aux send was a "tap" off a processed channel. Nodal processing allows you to apply unique EQ, dynamics, and delay to a specific "send node" without affecting the main channel.
Example: A vocal channel might be processed with a high-shelf boost for the FOH PA, but that same channel can have a 3kHz notch applied at the node to the monitor aux to prevent feedback in the singer's IEMs.
3. Summing Math and Pan Law When a mono signal is panned center, it is sent to two channels (L and R). If sent at full power to both, the "center" would be 6 dB louder than the sides. Professional consoles use a -3 dB Pan Law (or -4.5/-6 dB) to drop the signal level as it moves center, ensuring a constant perceived volume (loudness) across the stereo field.
4. Digital Headroom in the 40-bit Floating Point Bus A 24-bit fixed-point bus provides 144 dB of dynamic range. However, summing 100 channels can exceed this. Modern engines use 40-bit or 96-bit Floating Point math for the mix bus. This allows for over 700 dB of internal headroom. You could theoretically peak your mix bus at +20 dB internally without clipping, provided you pull the "Master Fader" down before it hits the D/A converter.
II. Practical Lab: The Matrix Drive System
Tool: Console Offline Software.
Tasks: * Build a 6-output Matrix: Main L, Main R, Sub, Outfill L, Outfill R, Frontfill.
Patch the "Main Bus" into all matrix inputs.
Use Nodal EQ to apply a 250Hz cut on the "Drums" group send only to the "Sub" matrix.
III. Daily Assessment (Tuesday)
Q1: Describe a scenario where you would choose a -6 dB Pan Law over a -3 dB Pan Law.
Q2: Why does an FPGA console handle summing math differently than a CPU-based DAW?