Final answer:
A Bandstop Filter is the best device application to reduce ingress noise in a system, as it is designed to block specific frequencies associated with noise while allowing others to pass through.
Step-by-step explanation:
To reduce ingress noise in a system, the most effective device application from the options listed would be a Bandstop Filter. Ingress noise is unwanted radio frequency (RF) signals that enter the cable system through various sources, which can degrade signal quality. A Bandstop Filter, also known as a notch filter, is designed to block or filter out a specific range of frequencies. It allows all other frequencies to pass through but prevents the frequencies associated with ingress noise from entering the system. This makes it an ideal choice for reducing ingress noise.
Other options mentioned like a Signal Amplifier, Transmitter, and Modem do not primarily function to reduce ingress noise. A Signal Amplifier boosts the strength of the signal but can also amplify noise, a Transmitter is used to send signals, not filter them, and a Modem (modulator-demodulator) is used to modulate digital data over communication lines and does not typically deal with RF signal filtering.