DSP Routing Matrix
Canonical Definition
A routing matrix is a set of input-to-output coefficients and states that determines which input signals contribute to each output and by how much, commonly expressed as:
y_j = Σ g_ij x_iFor output j, every input i is multiplied by its coefficient g_ij, then the contributions are summed.
Routing Is Not The Same As Mixing
- Routing: decides which paths are connected.
- Coefficient or gain: decides each connected path's contribution.
- Mixing or summing: is the addition that occurs when more than one contribution feeds an output.
- Post gain: changes the completed output after the matrix.
- Mute: sets a path or output to zero, but its location matters.
Units Must Be Named
| Displayed value | Linear coefficient | Gain |
|---|---|---|
| 100% | 1.000 | 0 dB |
| 70.7% | 0.707 | approximately -3.01 dB |
| 50% | 0.500 | approximately -6.02 dB |
| 0% | 0 | mute / negative infinity dB |
A software field labeled “50” may mean percent, linear gain, dB, an index, or a manufacturer-specific scale. Record the native unit instead of assuming.
Safe 2-In / 4-Out Example
| Output | Input L | Input R | Purpose |
|---|---|---|---|
| 1 | 1.0 | 0 | Left reference path |
| 2 | 0 | 1.0 | Right reference path |
| 3 | 0.5 | 0.5 | Correlation-safe mono starting path |
| 4 | purpose-defined | purpose-defined | Processing or protected comparison path |
The 0.5 + 0.5 mono starting point keeps fully correlated, equal-amplitude content at the same voltage as one input. It is not the only valid choice: the intended source correlation, target level, and available headroom determine the final coefficients.
Common Routing Failures
- full-range audio routed to a tweeter output before protection is active
- left and right swapped at either the matrix or physical connectors
- one input reaching the same output through two parallel paths
- source-selection preset changing routing without changing labels
- post-matrix gain hiding the true coefficient or sum
- instant source switching creating a discontinuity or pop
Verification Sequence
- Mute amplifiers or disconnect sensitive drivers.
- Label physical outputs and DSP output channels.
- Feed one input with a low-level, band-limited signal.
- Unmute one matrix path and one output at a time.
- Verify physical connector, channel identity, level, polarity, and bandwidth.
- Repeat for every input and every preset.
- Enable sums only after individual routes are known.
- Record the matrix in its native units and save a known-good baseline.