Latency through the WING - Shadow Rack Docs

With a WING, the loop through the desk measures itself, and the mains on the rack stay in time, so the PA stays aligned.

Everything that goes through the rack arrives on the desk a little later than its direct source would. How much later is the sum of the trip over USB, the Mac's buffers and the plugins' own delay. Shadow Rack knows the last two exactly; the trip through the desk it measures - and with the WING Extension it does that by itself.

MAC and LOOP#

The LATENCY tile on the top bar shows two numbers:

MAC - what the Mac adds between USB in and USB out: the input plus output buffer, exact.
LOOP - the whole trip, measured: WING out → Mac → WING in. It includes the desk's USB conversion and the driver, which nothing can calculate. Until it's measured it says not measured.

Plugins add their own delay on top, per channel; each channel shows its total on its page (LATENCY 15.00 ms).

Measured by itself#

With the desk connected, LOOP is measured:

about 4 seconds after Shadow Rack connects to the desk;
whenever the interface, sample rate or buffer changes (once per setting).

For a moment Shadow Rack routes the highest free USB output straight back to the highest free USB input on the desk, plays a short, quiet chirp, listens for it for 0.6 seconds and puts the routing back as it was. The chirp never goes anywhere near the mains - nothing reaches the PA.

Setup > Audio: the WING over USB, LOOP measured (here the desk isn't on the network yet, so the box still shows the manual way)

In Setup > Audio#

The Running now panel shows the same numbers bigger:

LOOP (MEASURED) with Wing out -> Mac -> Wing in under it - or measuring right now... / measured by itself in a moment.
SLOWEST CHANNEL - the channel with the most plugin delay, and what it adds: +15.00 ms = 21.90 ms in all, LOOP included. That's the latest anything on the rack arrives on the desk.

The Measure the loop box says The Wing is connected: LOOP is measured by itself after connecting and whenever the buffer or sample rate changes ... and has one button, MEASURE AGAIN. While it runs: Measuring through the Wing... (a short, quiet chirp on a free USB channel - nothing reaches the PA); then Measured through the Wing: 331 samples (6.90 ms).

Without the network link to the desk (or without the extension) the box shows the manual way instead: route a USB output back to a USB input on the desk yourself, pick them under SEND ON / LISTEN ON and press MEASURE.

When it can't measure#

Message	What to do
No free USB input / output on the Wing for the test loop.	Free one USB channel each way on the desk
The Wing refused the test loop (...)	The desk said no - the message says what
The test sound didn't come back through the Wing.	Check the USB cable; press MEASURE AGAIN
Shadow Rack isn't using the Wing's USB audio (Setup > Audio).	Choose the WING as interface

Keeping the PA aligned#

When the mains feeding the speakers go through the rack, they have to stay in time with each other - a sub that arrives a few milliseconds before the tops is a different PA.

Every main you put on the rack joins the alignment group PA. Shadow Rack delays the faster mains in the group to the slowest one, to the sample. The main's page shows it in yellow, e.g. LATENCY 3.40 ms (plugins 0.00 + 3.40 PA) - its own plugins plus what it waits for the others.
Mains in use that aren't on the rack play early against the ones that are. On the On the rack and MAIN 1–4 routing pages Shadow Rack warns in red - Front goes through Shadow Rack, Sub doesn't: out of time by 3.4 ms. Put the whole PA on the rack and it's kept in time. - and offers PUT THE WHOLE PA ON THE RACK (routing).
DIRECT switches all the mains on the rack together, so they stay in time with each other on direct too.