Digital signal and image processing
Guess first
How fast must you sample a 20 kHz sound?
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Lesson notes
Key points
- The Nyquist theorem says you must sample at more than twice the highest frequency, so 20 kHz audio needs over 40 kHz.
- Sample slower and high frequencies fold back as false low tones called aliasing, which is why CDs use 44.1 kHz.
Definitions
- Aliasing
- Distortion where frequencies above fs/2 appear as false lower frequencies after sampling.
Takeaway: Sampling rate must exceed twice the highest signal frequency.
Quick check: Audio contains frequencies up to 20 kHz. What is the minimum sampling rate to avoid aliasing?
- 20 kHz
- Just over 40 kHz
- 10 kHz
Sample above twice the highest frequency, or aliasing appears.
Nyquist rateAliasing
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