buses, sidechain and formats

The one property every plugin must have before anything else: it negotiates its layout and accepts a sidechain, in both formats, in a real host. No amount of interface is worth building on top of a plugin that does not.

formats

VST3 and CLAP, on macOS, Windows and Linux.

	order ceiling	ambisonic layout	sidechain
VST3	7th: the format’s layouts stop there	the format’s ambisonic layouts, ACN	an aux input bus
CLAP	none of the format’s own	the ambisonic port extension, ACN and SN3D	an aux input port

CLAP comes through a patched version of clap-juce-extensions that describes ambisonic ports; the patch is bambi’s to maintain and is written to go upstream.

one rule for every plugin

• The main input is fixed. Mono or stereo for the encoder; the field, (N+1)² channels, for an effect.
• The main output is ambisonic, at the highest order that fits the channel count. Channels beyond it are silent.
• The sidechain is a real aux bus. Never a wide main bus read past its first pair: a host that sent a sidechain into channels 3 and 4 of a wide main input would have it land inside the signal.

A new plugin joins by declaring its buses. The checks are the same for all of them.

the conformance suite

tools/conformance.sh loads every installed plugin, in both formats, and asks each the same questions:

1. every layout it claims is accepted, and every layout it does not claim is refused;
2. a wide main input is refused, so a send on channels 3 and 4 can only be the sidechain;
3. the sidechain arrives, sample for sample, at every order;
4. unused output channels are silent;
5. renders are bit-identical at block sizes 1 to 1024;
6. an offline bounce equals realtime in every sample.

in a host

What a host actually does, found by running the plugins in one:

• Hosts often give a track only even channel counts. An order that needs an odd count then runs with a spare, silent channel: 10 channels are 2nd order and one unused.
• A host may size the sidechain bus to the track’s width, and route a send to its first pair. Refusing a wide main input is what makes that pair the sidechain.
• An effect’s sidechain comes after the field: at 3rd order, after the first 16 channels. Route to the channels after the field, and in some hosts map them onto the sidechain pins.
• A host’s own parameter slider may not reach an exact value. Exact entry belongs in the plugin’s own window, which is one reason every value is a box you can drag finely.
• Offline and realtime renders, with automation on every plugin, null to silence. A loop’s jump back is treated as a locate, and a host that splits its block at the loop’s end gives every pass the same start.

The settings page shows what the host negotiated: the sample rate, the channels in, out and on the sidechain, and the transport.