Abstract: A radio frequency (RF) modulation apparatus for modulating input video and audio signals into a television broadcast signal is provided. The apparatus includes a buffer amplifier, a decoder, a switching device, and an RF modulator. The buffer amplifier amplifies and stores the input audio signal as a stored audio signal. The decoder inputs and decodes the stored audio signal to produce a decoded audio signal. The switching device inputs the stored audio signal from the buffer amplifier and the decoded audio signal from the decoder and selectively outputs either the stored audio signal or the decoded audio signal as a selected audio signal. Specifically, the stored audio signal is output as the selected audio signal if the input audio signal corresponds to a stereophonic audio signal or an audio multiplexing signal. On the other hand, the decoded audio signal is output as the selected audio signal if the input audio signal corresponds to a mono audio signal.