VoIP Codec notes

G.711:

• 最普遍的codec
• 延襲於circuit switch的世界XD
• 又稱PCM(Pulse Code Modulation)
  
• one sample 8 bits, and PCM uses 8kHz sampling rate
  
• →8 bits * 8k Hz = 64 k bit per second (64 bps)

GSM
G.729
ADPCM(Adaptive Differential PCM)
DTMF(Dual-Tone Multifrequency) Digits
Nyquist sampling theorem(p86)