pipewire 1.4 latency math, finally written down

# round-trip latency on pipewire 1.4.x, RME UCX II, 48kHz

# verified with jack_iodelay against a 1m TRS loopback

# quantum (period) = configurable, suggested 256 or lower for tracking

# min-quantum is a floor; the node graph can’t request lower than this

# max-quantum is rarely the active value unless a node forces it

# configured:

# default.clock.rate = 48000

# default.clock.quantum = 256

# default.clock.min-quantum = 32

# default.clock.max-quantum = 8192

# measured round-trip (jack_iodelay):

# q=256 → 16.8 ms (= 2 * 256/48k + ~6ms ALSA padding)

# q=128 → 9.1 ms

# q=64 → 5.4 ms

# q=32 → 3.6 ms (xruns under chrome+browser load)

# the +6ms is alsa’s period-count safety margin. cutting periods

# from 2 to 1 saves ~5.3ms but pipewire refuses on most usb cards.

# tracking sweet spot: q=128, periods=2.

# mixing: q=1024+ to let plugin pdc compensate without xrun pressure.