  We revisit linear tidal excitation of spiral density waves in the disks of
cataclysmic variables (CVs), focusing on scalings with orbital Mach number in
order to bridge the gap between numerical simulations and real systems. If an
inner Lindblad resonance (ILR) lies within the disk, ingoing waves are robustly
excited, and the angular-momentum flux they carry is independent of Mach
number. But in most CVs, the ILR lies outside the disk. The wave flux and its
scaling with Mach number are then very sensitive to conditions near the disk
edge. If the temperature and sound speed vanish there, excitation tends to be
exponentially suppressed. If the Mach number remains finite in the outer parts
but the radial and vertical density scale lengths become comparable due to
subkeplerian rotation, resonance can occur with acoustic-cutoff and
stratification frequencies. These previously neglected resonances excite waves,
but the Mach-number scaling remains very steep if the radial scale length
decreases gradually. The scaling can be less strong - algebraic rather than
exponential - if there are sharp changes in surface density at finite sound
speed. Shocks excited by streamline-crossing or by the impact of the stream
from the companion are unlikely to be important for the angular-momentum
budget, at least in quiescence. Our results may also apply to circumplanetary
disks, where Mach numbers are likely lower than in CVs.
