AN4229 datasheet(8/26 Pages) STMICROELECTRONICS

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Vocoder overview and comparison

AN4229

8/26

DocID024112 Rev 1

1.6

Vocoder performance

Table 3 to Table 6 show measurements for G.711, G.726, IMA-ADPCM and Speex codecs.

Performance data are measured on STM32F4 device at System Clock equal to 168MHz

with 5 wait states and compilation optimization parameter set to high. Speex data

measurements are done on STM32F4DISCOVERY while all the other codecs are tested on

STM3240G-EVAL board.

Benefits

– Designed to deliver

precise

transmission of

speech

– Very low

processing

overheads

– Uses 32 Kbits

which is half the

rate of G.711 codec

and hence

increases the

usable network

capacity by 100%

– Very much used on

international trunks

in the phone

network

– Transmit only the

difference between

the real and the

predicted value

– Predict the current

signal value from

previous value

– Integration of NB

and WB in the

same bitstream

– Wide range of

bitrates

– Dynamic bitrate

switching and

ariable bitrate

(VBR)

– Voice activity

detection (VAD,

integrated with

VBR)

– Variable

complexity

– Intensity stereo

encoding option

Drawbacks

– Poor network

efficiency

– Lacks missing

packet interpolation

– Not well-suited for

sound effects

– Low compression

rate (equal to ¼)

– Quality is

permanently

degraded to

reduce file size

– By only specifying

quality parameter,

there's no guaranty

about the final

average bitrate

Table 2. Codecs comparison (continued)

Codec name

G.711

G.726

IMA-ADPCM

Speex

Table 3. G.711 performance

Parameter

G.711 encoder

G.711 decoder

µ-law

A-law

µ-law

A-law

Flash memory (bytes)

RAM (bytes)

Load (MHz)

0.38

0.3

0.22

0.2

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