The headend has several audio-video playback devices within it. What piece of equipment is required to assign their output signals to specific RF carriers on the CATV system?

A modulator takes the composite or component audio-video output from a source device and encodes it onto a designated RF carrier frequency, making it compatible with the broadband CATV channel plan. Each source device requires its own modulator assigned to a unique frequency so it can coexist with other channels. Without modulators, baseband A/V signals cannot be injected into the RF distribution plant.

A combiner merges already-modulated RF signals from multiple modulators into one output feed; it does not perform the frequency assignment or modulation of baseband A/V content.

A splitter passively divides an existing RF signal into multiple output paths and has no ability to convert baseband video to an RF carrier.

A multiport tap is a passive distribution device installed on the coaxial plant to provide subscriber drop connections, not to process or modulate source signals.