G722 Series Intro

There are three principal codecs, which are unrelated, but all carrying the G.722 label.

1.
G.722 is the original 7 kHz codec, using
ADPCM and operating at 48 – 64 kbit/s. （adaptive difference pulse code modulation自适应差分脉冲编码调制）

2. G.722.1, another 7 kHz codec, operates at half the data rate while delivering comparable or better quality than G.722, but is a transform-based codec.

based on
lapped transform technology, using a
Modulated Lapped Transform (MLT). （调制重叠变换）

G.722.1 Annex C is very similar to G.722.1, but provides twice the audio bandwidth, 14 kHz. (这儿的带宽的含义， 就是指采样率。32khz采样率)

3.
G.722.2, which operates on
wideband speech and delivers very low bitrates, is an
ACELP-based algorithm。（ACELP，是Algebraic Code Excited Linear Prediction的简称， 中文名：代数码本激励线性预测编码。）

G7221_7_24, G7221_7_32, G7221_14_24, G7221_14_32, G7221_14_48 中， 7， 14分别表示16khz, 32khz采样率， 而24, 32, 48分辨表示码率(kpbs)。