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Overview of the most important CODEC specifications:

Codec	Name	Data Rate	Frequency range	Quality
G.711	Pulse Code Modulation (PCM)	56 oder 64 kbit/s	300 bis 3400 Hz	ISDN
G.726	Adaptive Differential Pulse Code Modulation (ADPCM)	16-40 kbit/s	-	-
G.728	Low Delay Code Excited Linear Prediction (LD-CELP)	16 kbit/s	300 bis 3400 Hz	nearly ISDN
G.729/ G.729A	Conjugate Structure Algebraic Code Excited Linear Prediction (CS-ACELP)	8 kbit/s	300 bis 3400 Hz	better than G.723.1
G.723.1	Multiple Maximum Likelihood Quantization (MPMLQ)	6,3 kbit/s	300 bis 3400 Hz	Good
G.723	Algebraic Code Excited Linear Prediction (ACELP)	5,3 kbit/s	-	-
Speex Narrowband	Free patent audio compression (free)	4 - 15 kbit/s	8 kHz	medium GSM
Speex Wideband	Free patent audio compression (free)	10 - 28 kbit/s	16 - 32 kHz	better GSM
DVI4	Adaptive Differential Pulse Code Modulation (ADPCM)	32 kbit/s	8 kHz	-
iLBC	Internet Low Bandwidth Codec (free)	13,3 kbit/s	8 kHz	better G.729
G.722.1	MLT	24 kbit/s	16 kHz	-
l16 PCM	Linear PCM at 16 bits per sample	128 kbit/s	-	-
EVCR	Enhanced Variable Rate Codec	8 kbit/s	-	-
H.263	Videocodec DCT	16-256 kbit/s	-	-
H.261	Videocodec DCT	64-256 kbit/s	-	-

CPU load

All codecs stated above use different encoding algorithms. As a matter of fact, a specific number of CPU operations per second are executed by these algorithms. Here's an example of the number of CPU instructions or four popular codecs (in MIPS = million instructions per second):

Codec	G.711	G.723.1	G.729	G.729A
Bandwidth (kbit/s)	64	6,3	8	8
computing power (MIPS)	<1	16	50	10,5