Filters — do they pass all frequencies?

Introduction / Context:
Filters are designed to selectively pass certain frequency ranges while attenuating others. This item checks a basic definition that underlies audio, RF, and signal-processing practice.

Given Data / Assumptions:

• Filter categories include low-pass, high-pass, band-pass, and band-stop (notch).
• Real filters have finite roll-off and non-ideal ripple or phase characteristics.

Concept / Approach:
By definition, a filter does not pass all frequencies equally; it shapes the spectrum. The passband is defined where gain is near unity (or specified level), and the stopband where signals are significantly attenuated.

Step-by-Step Solution:

Verification / Alternative check:
Examine a magnitude response plot (|H(jω)| vs. ω). You will see defined pass/stop regions, not a flat “all-pass” transmission unless a specific all-pass filter is intentionally designed (which still alters phase).

Why Other Options Are Wrong:

• “True” would describe an ideal wire or unity buffer, not a filter. Even an all-pass filter modifies phase rather than passing all frequencies unchanged in every respect.

Common Pitfalls:
Equating “filter” with “removes noise” generically; correct design requires selecting the passband/stopband to match the signal and noise spectra.

Final Answer:
False