1. 4.1 Different Audio Properties
2018/6/22
4.1 Different Audio Properties
Edited by Arthur Fung 4D20

2. Sampling rate (取樣頻率) the number of samples(取樣) per second.
Sample rate, sampling frequency also means sampling rate.
the unit(單位) is Hz.

3. Sampling rate - examples
8kHz – for telephone use 44kHz – for (Video) Compact Disc-audio 48kHz – for Digital Versatile Disc-audio 96kHz – for HD-DVD-audio & BD-ROM-audio

4. Sampling rate
The advantages of high sampling rate: The sound quality is more like the real.
The disadvantages of high sampling rate The audio file may take up(佔用) more disk space.

5. Sampling rate
Remember that: Sampling rate is not same as bit rate(比特率). Bit rate is the number of bits that are processed per unit of time.
Also, 1kHz = 1000Hz ≠ 1024Hz (Extra: 1K(kilobi)=1024, 1k(kilo)=1000)

6. Sampling rate
Extra: As human cannot hear frequencies above about 20kHz, so 44.1kHz is the most common sampling rate because it includes all human frequencies (20Hz-20kHz).

7. Sample size (取樣解像度)
Definition of sample size is that the number of digits(數位) in the digital representation(數位表現) of each sample.
Sample format also means sample size.
And the unit is Bit(b).
The following is the common sample size: 16bits – Audio CD

8. Sample size
The advantages of high sample size: The dynamic range, which means the sound can be louder and can be softer, will increase because of high sample size.

9. Audio Channel (聲道) The definition of audio channel is that the sound
The common numbers of audio channels are: 1 – Mono 2 – Stereo 3(2.1) – Stereo + Subwoofer 6(5.1) – Dolby Digital 8(7.1) – Dolby Digital EX

10. Audio Channel
The advantage of many audio channels: The positions of sounds will be more real.
The disadvantage of many audio channels: It will take up more disk space.

11. How to calculate the size of an audio file?
The formula of calculation the size(have not zipped) is: (Sampling rate × sample size × audio channels × the length of time) ÷ 8 For example: If an audio file, the length of time was 1min, the sampling rate is 48kHz, the sample size is 16bit, and that is a stereo audio. Calculate the size of the audio file.

12. How to calculate the size of an audio file?
The sampling rate = 48kHz, the sample size = 16bit, audio channels = 2 the length of time = 60 seconds Solution: (Sampling rate × sample size × audio channels × the length of time) ÷ 8 =(48 × 1000) × 16 × 2 × 60 ÷ 8 = bytes =11MB

13. Questions (Calculation)
An audio file, the length of time was 20min, the sampling rate is 96kHz, the sample size is 32bit, and that the use of technology is Dolby Digital. Calculate the size of the non-zipped audio file. (please value to 1) A. 3GB B. 8GB C. 15GB D. 21GB

14. Questions (Calculation)
An audio file, the length of time was 20min, the sampling rate is 96kHz, the sample size is 32bit, and that the use of technology is Dolby Digital. Calculate the size of the non-zipped audio file. (please value to 1) A. 3GB B. 8GB C. 15GB D. 21GB

15. Reference http://en.wikipedia.org/wiki/Sampling_rate
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