Fundamentals of Audio Production

1. Fundamentals of Audio Production Chapter Three: Digital Audio Fundamentals of Audio Production. Chapter 3

2. Converting analog to digital • ADC – analog to digital conversion • An analog voltage is converted in binary code • Binary = “two states” • Expressed as “1/0” or “on/off” • Each digit is called a bit • Bits are combined into longer binary numbers or “bit words” Fundamentals of Audio Production. Chapter 3

3. Converting analog to digital • If a single digit were used to express the voltage values – there would be only two values • By creating clusters of binary digits in longer strings, many values may be represented • Two digits could describe four values: 00 – 11 – 10 – 01 Fundamentals of Audio Production. Chapter 3

4. Converting analog to digital • The number of digits in the binary number or “bit word” is called the bit rate • For many years the standard for consumer audio (compact disks) has been 16-bit, or binary numbers with sixteen digits • 16-bit sampling will allow over 65,000 various combinations of digits • 16-bit sampling produces acceptable fidelity for most puposes Fundamentals of Audio Production. Chapter 3

5. Converting analog to digital • Another variable which determines the accuracy of analog to digital conversion is the sampling rate • Sampling rate describes how frequently the analog voltage is measured and converted into digital data Fundamentals of Audio Production. Chapter 3

6. Nyquist Principle • The Nyquist principle states that the highest frequency that can be sample is one half the sampling rate • Thus, a sampling rate of 44,100 samples per second would accurately reproduce frequencies up to 22,050 Hz. • Since most humans hear frequencies no higher than 20,000 Hz, 44.1 is acceptable Fundamentals of Audio Production. Chapter 3

7. Sampling rate Each red point along the timeline represents one sample Fundamentals of Audio Production. Chapter 3

8. Sampling rate A low sampling rate induces sampling error represented here as a misshapen wave form Fundamentals of Audio Production. Chapter 3

9. Sampling rate A higher sampling rate reduces sampling error represented here as a more accurate wave form Fundamentals of Audio Production. Chapter 3

10. Digitization • At best, the digital data set is an approximation of the analog voltage that was sampled • Converting the digital data back into an analog signal will have some inherent error Fundamentals of Audio Production. Chapter 3

11. Digitization Over sampling and higher sampling rates produce more accurate wave forms Fundamentals of Audio Production. Chapter 3

12. Data management • High fidelity audio (wide frequency response and high dynamic range) requires large data sets • To accommodate high fidelity audio, high capacity storage systems are necessary Fundamentals of Audio Production. Chapter 3

13. Data management • Down sampling or down conversion lower the sampling and bit rates to produce smaller files • To help manage data, compression schemes remove redundancies and use “masking” of some content Fundamentals of Audio Production. Chapter 3

14. Data management • 44.1 Khz .WAV file • 22.1 KHz .WAV file • 11.8 KHz .WAV file • 8.8 KHz .WAV file • 16 KHz .AU file • 22.1 KHZ .MP3 file Fundamentals of Audio Production. Chapter 3