Audio Devices

An audio device plays show audio out of WATCHOUT — either to a sound output on the node, or as a stream over IP to any number of listeners on the network. Each audio device uses one of four audio interfaces: WASAPI, WASAPI Exclusive, ASIO, or Dante. Which interfaces are available for a given physical audio device depend on its driver — many professional audio devices expose both WASAPI and ASIO, so the choice comes down to the latency and exclusivity you need rather than the hardware itself. A node can host as many audio devices as its hardware supports.

Per-interface behavior is documented on the dedicated pages: WASAPI, WASAPI Exclusive, ASIO, Dante. This page covers the parts shared by every audio device — buses, channels, format, latency, and routing.

Audio Buses

Audio buses are the middle layer between audio cues and audio devices. A bus is a named, numbered channel that lives at the show level — it has nothing to do with any particular device or node. Cues send audio to a bus; audio devices receive audio from buses and play them out through their physical channels.

This indirection is what lets the same show run on different hardware. A cue that targets the "Voice-Over" bus doesn't need to know whether the playback rig has a stereo USB interface, a 16-channel ASIO card, or a Dante network — it just produces audio for that bus. The audio device's routing matrix decides which physical output channels carry which buses, and you can change that mapping per venue without touching a single cue.

What ships by default. A new show comes with two buses named Left and Right. The default routing matrix on every audio device sends the Left bus to channel 1 and the Right bus to channel 2, so stereo playback works out of the box without any per-device configuration.

Configuring buses. The bus list lives at the show level, not on any device. Open Edit → Preferences (or Show Properties) and find the Audio Bus section:

• Count sets the total number of buses in the show. Increasing it appends new buses at the end of the list, each pre-named with its bus number ("3", "4", and so on). Decreasing it removes buses from the end — but only if those buses are not referenced anywhere. If a bus is still in use by an audio cue, a capture source, or an audio device's routing matrix, the count change is rejected.
• Names — click any bus name in the list to rename it inline. Use names that describe the logical audio path in your show: Voice-Over, Music, SFX, Center, IEM-Stage-Left, Stage Manager Foldback. Any number of devices can subscribe to a bus through their own routing.

How cues address buses. Audio cues, media cues with audio, and capture sources that carry audio all target buses by name and number. See Audio Volume for the cue-side level control and Adding Media Cues for how media cues are placed.

How devices receive buses. Every enabled audio device on every node receives every bus simultaneously. Whether the bus reaches a physical output depends on that device's routing matrix — by default each bus routes 1:1 to the device's channel of the same number scaled by masterVolume, so on a stereo WASAPI device the Left bus comes out of channel 1 and the Right bus out of channel 2. Override the matrix to summing, redirect, or silence specific bus → channel combinations.

Adding an Audio Device

From the Devices window:

1. Click Add → Audio Device.
2. In the General section, set the Name and assign the Node that hosts the sound hardware.
3. In the Audio section, choose the Device Type (driver).
4. Pick the Device (or Adapter for Dante), the Channels, and the Format.
5. Enable the device with the heart icon when configuration is complete. Audio devices start disabled by default.

The Refresh button (the circular arrow next to Device Type) re-queries the node for available devices, adapters, channel counts, and sample formats. Use it when new hardware is connected, when a Dante adapter is added, or when the device list looks stale.

Audio Interfaces

An audio interface here means the software interface WATCHOUT uses to talk to the sound hardware — not the hardware itself. WATCHOUT supports the modern Microsoft audio APIs (WASAPI in shared and exclusive mode), Steinberg's professional ASIO standard, and Audinate's Dante for network audio. It does not use the older WDM-based paths (MME, DirectSound, kernel streaming) that some legacy media-playback applications still expose; those have been superseded on Windows by WASAPI.

Choosing Between WASAPI and WASAPI Exclusive

Both work on the same hardware; pick whichever fits the deployment. WATCHOUT compensates for driver latency through the per-device Latency slider, so absolute latency rarely drives the choice. The practical differences are compatibility and mixer behaviour:

• WASAPI Shared (the UI option labelled just WASAPI) is the more compatible choice. Windows handles sample-rate and bit-depth conversion behind the scenes, so almost any format combination works. Other applications keep access to the device. Good when WATCHOUT needs to coexist with system audio, or when you want the broadest format support without fighting the vendor control panel.
• WASAPI Exclusive runs the device at its native format only, and how many formats are exposed in the dropdown depends entirely on what the driver advertises for exclusive use — usually a smaller list than shared mode accepts. In return, the Windows mixer is bypassed and nothing else can play through the device while WATCHOUT holds it. Good when nothing else on the node should reach the audio output.

If the sample rate or format you expect isn't in the dropdown under WASAPI Exclusive, the driver simply doesn't advertise that combination for exclusive use. Fall back to WASAPI Shared (where Windows can convert), or check the vendor's audio control panel to see what the device supports natively.

ASIO vs. WASAPI on Multi-Channel Cards

Where ASIO and WASAPI differ in a way that affects show setup is how the physical audio device's channels are exposed:

• ASIO typically presents the whole card as one interface. A single WATCHOUT audio device addresses every channel.
• WASAPI / WASAPI Exclusive typically split a multi-channel card into separate stereo pair interfaces. WATCHOUT needs one audio device per stereo pair, and the show's buses route across them.

For a multi-channel destination from a single card, ASIO is the simpler path — one audio device, all channels in one place.

Sync within a device vs. between devices. All channels of a single audio device share one sample clock — the channels within that device are sample-accurate to each other. Sync between separate audio devices on the same node depends on each device's clock; WATCHOUT aligns them to within about a millisecond, which is fine for almost any show, but the exact behaviour is driver-dependent.

This matters for multi-channel hardware. Take an 8-channel physical audio device exposed by its WASAPI driver as four stereo pairs: in WATCHOUT you'd set up 4 audio devices, one per pair, with 8 buses routed across them. The two channels of each pair are perfectly synced because they share a clock; the four devices to each other can drift by sub-millisecond amounts. The same physical device under ASIO typically presents all 8 channels as one device — one clock, sample-accurate across all 8. For multi-channel music, surround mixes with tight phase requirements, or anything where channel groups must phase-lock, ASIO is the safer choice.

Channels and Format

• Channels — the number of output channels the device will publish. The available options depend on the driver and the selected device. Dante adapters offer fixed steps (2, 4, 8, 16, 32, 64); WASAPI / ASIO show whatever the hardware reports.
• Format — sample rate and bit depth shown as a combined choice (for example 48000Hz, 16 bit or 96000Hz, 32 bit). The dropdown lists what the selected device exposes. The fallback list when no device-specific information is available covers 44100 / 48000 / 96000 Hz at 16-bit and 32-bit.

These options follow a cascading validation: choosing a driver narrows the device list; choosing a device narrows the channel options; choosing a channel count narrows the available formats. Changes are rejected if they would leave the device in an invalid state — pick from the top down for predictable results.

Latency

The Latency slider (range -100 ms to +100 ms) offsets the audio output of this audio device relative to the rest of the show. Positive values delay the audio; negative values pull it forward.

The primary use is video sync (lipsync). Display chains — projectors, LED processors, scalers — almost always add a few frames of latency before the picture reaches the screen, while the local sound output is essentially instant. Without compensation the audio arrives noticeably ahead of the picture. Set the per-device Latency to match the display chain's delay so audio and video land together. Each audio device has its own slider, so you can dial in different offsets per output (for example main PA vs. in-ear monitor mixes vs. a Dante feed to a broadcast truck).

Latency can also compensate for buffering further downstream — mixing consoles, DSPs, networked audio receivers — anywhere along the path that adds a known delay.

Driver-intrinsic latency — what the underlying physical audio device adds before the audio reaches its outputs — depends on the interface type and is covered on each interface's page.

Audio Bus Routing

Below the device properties, the Audio Channel Mapping section shows a matrix of the show's audio buses (rows) against the device's output channels (columns). Each cell carries an expression that controls how that bus is mixed onto that channel. The default expression is masterVolume — a built-in variable (range 0–100) that defaults to 50. It scales every bus on the device.

Per-Channel Expressions

Because every cell is an expression, you can do much more than route a bus 1:1 to a channel:

• Static attenuation. Multiply by a scalar to permanently trim a channel. If the center channel in a surround mix is hot, set the cell to masterVolume * 0.6 — that channel runs at 60 % regardless of operator input.
• Variable-driven gain. Reference any show variable in the expression and the value updates live. For example, masterVolume * centerVolume lets a centerVolume variable wired to a MIDI fader, an OSC slider, or an ArtNet channel adjust the center attenuation in real time during the show. Set up the source variable in the Variables window and assign its External Key to the protocol your control surface uses.
• Per-bus / per-channel mixing. Combine buses into a single channel by putting non-zero expressions in multiple cells of the same channel column. Sum them, scale them, or mute one with a * 0 while bringing in another.
• Conditional muting. Multiply by a boolean-valued variable (1 or 0) to gate a channel on/off from a hardware switch or HTTP input.

Expressions follow the same syntax used elsewhere in WATCHOUT (the cue-side Audio Volume effect, tween expressions, and conditional cues). Built-in variables available in this context:

• masterVolume — the device's master gain variable. Defaults to 50 (range 0–100). Affects every channel on the device unless you remove it from a cell's expression.

The expression in each cell is independent — masterVolume in cell A and cell B refers to the same variable, but the cell's overall expression can scale or replace it differently. Set a cell to 0 to silence that bus→channel route entirely.

Practical Notes

• The matrix automatically resizes when you change the channel count or the show's bus count; existing routes are preserved where they still fit.
• The number of buses is set at the show level — see Audio Buses above.
• For cue-side audio level control (per-cue fades, ducking), use the Audio Volume effect instead of editing the matrix. The matrix is for the device-side mixdown.

Related

• WASAPI, WASAPI Exclusive, ASIO, Dante Audio — per-driver pages.
• Audio Volume — per-cue audio level control.
• Show Properties — the show-level audio bus count.