What happens when audio containing a 25 kHz tone is recorded at a 44.1 kHz sample rate without an anti-aliasing filter?
AThe tone is captured faithfully
BThe tone is silently discarded
CThe tone folds back into the audible spectrum as a false frequency
DThe sample rate automatically increases to accommodate the tone
Aliasing occurs when signal frequency exceeds Nyquist (22.05 kHz at 44.1 kHz). The 25 kHz tone aliases to 44.1 - 25 = 19.1 kHz — an audible artifact not in the original audio.
Question 2 True / False
True or false: The Nyquist frequency equals the sample rate.
TTrue
FFalse
Answer: False
The Nyquist frequency is half the sample rate. At 44.1 kHz, the Nyquist frequency is 22.05 kHz. Frequencies above that cannot be faithfully sampled.
Question 3 Short Answer
What is oversampling, and what problem does it solve?
Think about your answer, then reveal below.
Model answer: Oversampling means digitizing at a multiple of the target rate (e.g., 8x or 16x), then downsampling digitally. It allows gentler digital anti-aliasing filters instead of steep analog filters, reducing phase distortion in the passband.
Steep analog anti-aliasing filters cause phase ringing near the cutoff frequency. Oversampling shifts the anti-aliasing problem into the digital domain where linear-phase filters can be used.
Question 4 Multiple Choice
A sound designer records foley at 96 kHz but delivers at 48 kHz. What must happen during the conversion?
AThe file must be pitch-shifted down by one octave
BContent above 24 kHz must be filtered before halving the sample count
CBit depth must also be halved
DNo conversion is needed — 96 kHz files play fine at 48 kHz
Downsampling from 96 kHz to 48 kHz requires filtering all content above 24 kHz (the new Nyquist) to prevent those frequencies from aliasing into the audible band during the sample-count reduction.