Sound Design Sound 5 — Questions and Answers
Question 1: In digital audio, the Nyquist theorem states that to accurately capture a frequency f, the sample rate must be:
- Equal to f
- At least 1.5 times f
- At least 2 times f (Correct answer)
- At least 10 times f
Correct answer: At least 2 times f
The Nyquist theorem requires a sample rate of at least twice the highest frequency to be reproduced in order to avoid aliasing artifacts.
Question 2: Aliasing in digital audio is caused by:
- Using too high a bit depth
- Sampling frequencies above the Nyquist limit, which fold back into the audible range (Correct answer)
- Excessive dithering during quantization
- Phase misalignment between audio channels
Correct answer: Sampling frequencies above the Nyquist limit, which fold back into the audible range
When a signal contains frequencies above half the sample rate (Nyquist frequency), those frequencies fold back and appear as false lower-frequency artifacts called aliases.
Question 3: What is the purpose of dithering in digital audio?
- To increase the sample rate of a recording
- To add low-level noise that randomizes quantization errors and reduces audible distortion (Correct answer)
- To remove noise from a digital recording
- To synchronize audio and video tracks
Correct answer: To add low-level noise that randomizes quantization errors and reduces audible distortion
Dithering adds a small amount of noise to a signal before reducing bit depth, which randomizes quantization errors and prevents them from becoming correlated, audible distortion.
Question 4: In digital audio, bit depth primarily determines:
- The highest frequency that can be recorded
- The dynamic range and resolution of amplitude values (Correct answer)
- The number of audio channels
- The file size per second of audio
Correct answer: The dynamic range and resolution of amplitude values
Each additional bit of bit depth adds approximately 6 dB of dynamic range; 16-bit audio yields ~96 dB and 24-bit yields ~144 dB of theoretical dynamic range.
Question 5: Which file format stores audio data without any compression, preserving the exact original samples?
- MP3
- AAC
- WAV (PCM) (Correct answer)
- OGG Vorbis
Correct answer: WAV (PCM)
WAV files using PCM (Pulse Code Modulation) encoding store raw uncompressed audio samples, making them lossless and bit-for-bit accurate.
Question 6: When a digital audio workstation processes audio at 32-bit floating point internally, the main advantage over 24-bit integer is:
- Lower CPU usage
- Ability to exceed 0 dBFS temporarily without clipping distortion (Correct answer)
- Higher sample rate support
- Better noise floor below −144 dBFS
Correct answer: Ability to exceed 0 dBFS temporarily without clipping distortion
32-bit floating-point representation allows values outside the 0 dBFS ceiling to be stored without clipping, providing headroom for intermediate processing stages.
Question 7: Sample rate conversion (SRC) is needed when:
- Changing the pitch of an audio file
- Transferring audio between systems operating at different sample rates (Correct answer)
- Converting mono audio to stereo
- Adjusting the loudness of a master file
Correct answer: Transferring audio between systems operating at different sample rates
Sample rate conversion re-samples audio data so it plays back correctly when the source and destination systems use different sample rates (e.g., 48 kHz vs. 44.1 kHz).
Sound Design Sound 5
In digital audio, the Nyquist theorem states that to accurately capture a frequency f, the sample rate must be: