Mud pulse telemetry systems and methods that employ some combination of modulated pulse positions, modulated pulse widths, and modulated pulse amplitudes to increase telemetry data rates. In at least some of the employed coding techniques, information is conveyed by the positions of both the upward and downward transitions. In some embodiments, fixed symbol intervals are used to convey combinatorial coded waveforms. In other embodiments, variable length symbol intervals include both a pulse position interval and a pulse width interval. The two intervals can be independently varied to convey telemetry data. Subject to specific system constraints, optimal coding efficiencies may be expected at data rates of between four and seven bits per symbol interval.