AU EngineCore
Reference Manual

Design Principles

Channel Path

Each channel is independent. Pre-fader inserts process the raw signal before level is applied; post-fader inserts receive the levelled signal. This distinction is significant for dynamics processors: a compressor placed pre-fader tracks the source, not the fader position.

Bus Path

Buses are first-class signal processors. A bus can carry a monitor mix, an effects return, or a submix routed to another bus. Buses operate simultaneously, each capable of hosting a full insert chain.

Hardware Output

The signal leaves the audio chain through hardware output pairs assigned per bus. A single bus can feed one stereo output pair. Multiple buses can share an output pair by accumulation, allowing parallel mix topologies without additional routing hardware.

Output assignment is non-destructive. Changing an output pair takes effect at the next audio buffer boundary with no dropout.

Routing Topology

Controls

Inserts

Inserts are loaded by tapping Add Insert at the bottom of the inserts section. The system AU browser appears; any compatible Audio Unit installed on the device is available.

Loaded inserts can be:

• Bypassed individually — tap the plug-in row to toggle bypass state
• Opened for editing — double-tap to open the plug-in editor
• Moved to pre- or post-fader position — available in the insert options sheet

AU EngineCore processes channels simultaneously, each with an independent insert chain. The audio engine allocates a dedicated processing slot per plug-in instance; no sharing occurs between channels or buses.

Performance Considerations

AU plug-ins vary significantly in DSP cost. The CPU meter in the toolbar reflects real-time render load as a percentage of the available buffer window. At 128-frame buffer depth and 48 kHz sample rate, the render window is approximately 2.7 ms.

Practical guidance for 8-channel live use:

• Gate and EQ processors are typically negligible — one or two per channel adds less than 2% load
• Convolution reverb and high-order dynamic processors are more costly — monitor CPU when loading
• If load exceeds 70%, increase buffer size in Settings before adding additional inserts

Creating and Removing Buses

Tap the + button in the bus section header to add a new bus. A default hardware output pair is automatically assigned if one is available. Buses are appended to the right of the existing bus order.

To remove a bus, open Bus Options by tapping the bus name, then select Remove Bus. Channels that had sends to the removed bus retain their send level settings; the sends become inactive until a replacement bus is created.

Bus Strip Controls

Output Routing

Each bus routes its output to one of:

• A hardware output pair on the connected interface
• Another bus (return send topology)
• No output — the bus processes internally and contributes to its return-send destinations only

Return sends allow effects chains to be centralised. For example, a reverb bus receives sends from multiple channels, processes them through a single reverb instance, and routes the wet signal back into the master bus at the desired level. This reduces plug-in count and DSP load compared to per-channel insert reverb.

Master Bus

One bus is designated as the Master. The Master bus feeds the recording engine directly, independent of hardware output configuration. This allows recording to capture the final mix regardless of which hardware output pair the master is routed to.

The Master bus is identified by the REC button in the mute row. Recording controls — start, stop, format, and segment duration — are all accessible from the Master bus strip.

Loading Plug-ins

Tap Add Insert in any channel or bus strip. The AU browser lists all compatible Audio Units grouped by manufacturer. Select a plug-in to instantiate it; it appears at the bottom of the insert chain and is active immediately.

Plug-ins are loaded per-strip. A compressor loaded into Channel 1 is an independent instance from the same plug-in loaded into Channel 2. Preset state is saved independently per instance.

Editor Access

Double-tap a loaded insert row to open the plug-in editor in a sheet. The editor is the plug-in's native UI — AU EngineCore does not modify or wrap it. Parameter changes made in the editor take effect immediately.

The editor sheet can remain open while the session runs. Adjusting parameters while audio is active is supported; no audio interruption occurs on editor open or close.

Bypass and Pre/Post Position

Each insert has two independent states:

• Bypass — the plug-in is excluded from the signal path; its DSP thread allocation is released
• Pre-fader / Post-fader — determines whether the insert processes before or after the strip fader

Both states are accessible from the insert options sheet, opened by long-pressing the insert row. State changes are parameter-snapshot safe — bypassing a plug-in does not modify its internal preset.

Compatibility

AU EngineCore supports effect-type Audio Units. Instruments and MIDI processors are not applicable in this version. Plug-ins must declare stereo or mono-to-stereo processing capability.

If a previously loaded plug-in is unavailable at session load (uninstalled or licence expired), the insert slot displays a placeholder. The slot remains in the chain at its position; audio passes through unprocessed as if bypassed. Reinstalling the plug-in restores full operation.

Auto-Save

AU EngineCore writes the current state automatically every 3 seconds when any parameter has changed since the last write. Auto-save is non-blocking — it runs without interrupting audio or UI responsiveness.

The auto-save target is the last manually saved scene. If no scene has been saved, the state is written to an internal recovery slot named after the connected hardware. This slot is loaded automatically at the next application launch with the same hardware connected.

Manual Save and Recall

Open the Scene browser from the toolbar. To save the current state, tap Save As and enter a name. Scenes are listed chronologically with the last-modified timestamp. Tap any scene to recall it.

The audio engine continues running during scene load; channels that already exist retain their signal path. New channels and buses are inserted at the next buffer boundary. The transition is inaudible under normal operating conditions.

Scene Contents

Starting a Recording

Tap the REC button on the Master bus strip. Recording begins at the next buffer boundary — there is no pre-roll. The button transitions to a lit state; elapsed time is displayed below it in real time.

To stop, tap REC again. A short fade is applied to the tail of the recording to prevent a hard cut on stop (only in segment recording). The file is written to the application's Documents folder and is accessible via Files.

Format Selection

Recording format is set in Settings. Available formats:

Segmented Recording

Segmented recording splits the output into fixed-duration files automatically. Set a segment duration in Settings (in minutes); when the current segment reaches the set duration, a new file begins seamlessly. The transition between segments is sample-accurate.

Segmented mode is useful for long sets where a single large file presents storage or import risk. Each segment is a complete, independently playable file.

Audio Engine

Recording

Display

Gestures

Toolbar Icons

Status Indicators