4. Encoding and Modulation

Question 1

Modulation Parameters

Answer 1

• frequency
• amplitude
• phase

Question 2

Pulse Modulation Methods (Pulse-Width Modulation PWM)

Answer 2

• pulse width determined by sample amplitude
• larger amplitude = larger pulse width

Question 3

Pulse-Postion Modulation (PPM)

Answer 3

• distance between two pulses reflects amplitude
• larger amplitude = more space between pulses

Question 4

Pulse-Amplitude Modulation (PAM)

Answer 4

• pulse amplitude varies with sample amplitude
• very susceptible to noise
• requires ideal condition

Question 5

Pulse-Code Modulation (PCM)

Answer 5

standard for digital audio
- each sample expressed as n-bit binary number (16, 24, or 32 bits)
- presence of pulse = 1, absence = 0
- only needs 16/24/32 clock cycles between samples
- lossless transmission

Question 6

PCM Bandwidth Calculation

Answer 6

bitrate = sample rate x bit depth x number of channels

examples:
- CD quality stereo: 44,100 x 16 x 2 = 1411.2 Kbps
- High-res mono: 96,000 x 32 x 1= 3072 Kbps