Twice the base rate: two units per matra, so a phrase occupies half its original span. The first layakari every student learns, and the workhorse ratio of the repertoire — kaida themes are routinely stated in barabar and developed at double rate.
The standard exercise is seamless alternation: one avartan in barabar, one in dugun, keeping the tala's landmarks fixed. The failure mode is drifting the underlying laya when the density doubles; the lehra or the clap pattern is the check.