Buses and Sends
A mixer is not just strips. It is a routing graph that sums and groups them.
Buses are the shared destinations. Sends are the taps that send signal to them.
Getting these two right is what turns a pile of strips into a controllable mix. This page grounds the routing model in libsonare's Bus and send processors; for the gentler intro see Mixing Basics.
Buses: master, aux, submix
A bus is a destination that sums several signals. libsonare gives a bus a role:
- Master — the final stereo output everything eventually reaches.
- Aux — the return for sends, where a shared effect (one reverb, one delay) lives.
- Submix — a group that collects related tracks (all the drums) so you can process and ride them as one.
A compressor on a drum submix glues the kit together; one fader then controls the whole kit. The master is special only in that it is the last bus in the graph.
Sends: parallel copies
An insert processes a track in series — the whole track passes through it. A send is different: it routes a copy of the track in parallel to a bus. Use sends for effects several tracks share, so a vocal, snare, and guitar can all sit in one reverb space without each carrying its own reverb.
Pre-fader vs post-fader
A send taps either before the fader or after it, and this is the routing decision people most often get wrong:
| Tap | Follows the fader? | Use for |
|---|---|---|
| Pre-fader | No | Headphone/cue mixes, effects that should stay constant while you ride the fader |
| Post-fader | Yes | Reverb/delay that should stay proportional to the balance |
VCA groups vs submixes
A submix re-routes audio: the grouped tracks actually flow through the submix bus. A VCA group does not — VCA (voltage-controlled amplifier) is the console circuit this borrows its name from, and here it means a single fader that trims several tracks' levels at once without changing where their audio goes. Use a VCA when the parts must still reach different buses but you want one hand on their combined level.
How libsonare models routing
Buses are Bus objects carrying a BusRole (Master/Aux/Subgroup) and run a BusProcessor; FxBus hosts shared effects. There is no submix role value: at scene level the role field is a free string in which only master is interpreted specially, so submix, subgroup, group and anything else all compile to the same generic non-master bus (the built-in drum-bus preset writes "subgroup"). A SendProcessor taps a strip at a TapPoint chosen by SendTiming (pre/post-fader) and feeds a destination bus. VcaGroup applies a shared gain offset across member strips without re-routing audio. The whole graph — strips, buses, sends, connections — is described by a serializable scene and runs with plugin delay compensation (PDC) so parallel paths stay time-aligned. See Mixing Scene JSON for the field-level format.
Related: Mixing Basics, Channel Strip, Automation and Metering, Mixing Scene JSON