RMAUG Professional Development Series2/11/09

Dwight Reifsnyder

2

“If you have an apple and I have an apple and we exchange apples then you and I will still each have one apple. But if you have an idea and I have an idea and we exchange these ideas, then each of us will have two ideas.”

George Bernard Shaw

Codec background and concepts Comparisons and basic features Voice Codec specifics Application in an Avaya environment

Codec is short for Coder/Decoder

Just like a Dick Tracy!

But what are the concepts involved?

Examples of coding include:◦ Pictures◦ Writing◦ Music◦ Language translation◦ Encryption

1876 Alexander Graham Bell ◦ Audio to electricity

1894 Guglielmo Marconi◦ Audio to radio

1916 Theodore Case◦ Audio to optical

An analog or analogue signalis any continuous signal for which the time varying feature (variable) of the signal is a representation of some other time varying quantity, i.e. analogous to another time varying signal. Analog is usually thought of in an electrical context; however, mechanical, pneumatic, hydraulic, and other systems may also convey analog signals

1937 - Alec H. Reeves ◦ Pulse Code Modulation invented (PCM)

1942 - John V. Atanasoff, Clifford Berry◦ First computer

1962 – Bell Labs◦ PCM first used in commercial telephony

A digital system uses discrete (discontinuous) values, usually but not always symbolized numerically (hence called "digital") to represent information. By contrast, non-digital (or analog) systems use a continuous range of values to represent information.

The word digital is most commonly used in computing and electronics, especially where real-world information is converted to binary numeric form as in digital audio and digital photography.

Analog◦ Continuous, modulates in direct relation

to original data

Digital◦ Discrete data (individual values) with no intuitive

or obvious correlation to original data

Encoding is changing form. Data may be encoded, transmitted, stored, and decoded

Analog (encoding or transmission)

Digital (encoding or transmission)

TIF (TIFF) Tagged Image File Format

PNGPortable Network Graphic

GIFGraphics Interchange Format

JPG (JPEG)Joint Photographic Experts Group

TIF (TIFF) 576K

NoCompression(lossless)

PNG232K

NoCompression(lossless)

GIF97K

Compressed(lossy)

JPG (JPEG)105K

Compressed(lossy)

If the pictures all look the same, why do we need different Codecs?

Different types of Codecs are optimized for different types of data

GIF uses Run Length Encoding (RLE)

AAAABBBBBCCCCDDDDDDEEEEEEEE4A4B4C6D8E

Max of 256 colors, fewer colors=smaller file

JPG uses multiple steps

We should create 8x8 DCT matrix using this formula:

DCT = 1/sqr(N),

if i=0 ij DCT = sqr(2/N)*cos[(2j+1)*i*3.14/2N],

if i > 0 ij N = 8, 0 < i < 7 , 0 < j < 7

in result we have:

DCT =

|.353553 .353553 . 353553 .353553 . 353553 .353553 .353553 .353553|

|.490393 .415818 .277992 .097887 -.097106 -.277329 -.415375 -.490246|

|.461978 .191618 -.190882 -.461673 -.462282 -.192353 .190145 .461366|

|.414818 -.097106 -.490246 -.278653 .276667 .490710 .099448 -.414486|

|.353694 -.353131 -.354256 .352567 .354819 -.352001 -.355378 .351435|

|.277992 -.490246 .096324 .416700 -.414486 -.100228 .491013 -.274673|

|.191618 -.462282 .461366 -.189409 -.193822 .463187 -.460440 .187195|

JPG (JPEG)Quality “100” 105k

JPG (JPEG)Quality “30” – 16K

GIF 256 Colors (lossless)97k

GIF 32 Colors (lossy)17K

There are many codec choices – the goal is for it to be transparent to the user

Codecs can contain multiple encoding/compression steps

Codec choice should consider type of audio, available bandwidth, and CPU usage

There a many audio codecs ◦ Quicktime◦ Real Player◦ MP3

Voice Specific Codecs◦ Industry Standard (ITU)◦ Optimized for speech

ITU-T Codec Standard

Coding Scheme Used

Bit Rate Encoding Delay Time

Mean Opinion Score

G.711 PCM 64 kbps <1 msec 4.7

G.722 SB-ADPCM 64 kbps 4 msec 4.5 

G.726 ADPCM 32 kbps 1 msec 4.2

G.728 LC-CELP 16 kbps 2 msec 4.2

G.729 CS-ACELP 8 kbps 15 msec 4.2

G.723.1 MPMLQ 6.3 kbps 37.5 msec 3.98

G.723.1 ACELP 5.3 kbps 37.5 msec 3.5

For most users, the main consideration in choosing a codec is bandwidth

This can be complex when considering calls between multiple regions

http://marketingtools.avaya.com/knowledgebase/ipoffice/general/bandwidth/

ITU-T Codec Standard

Coding Scheme Used

Bit Rate Encoding Delay Time

Mean Opinion Score

G.711 PCM 64 kbps <1 msec 4.7

G.722 SB-ADPCM 64 kbps 4 msec 4.5 

G.726 ADPCM 32 kbps 1 msec 4.2

G.728 LC-CELP 16 kbps 2 msec 4.2

G.729 CS-ACELP 8 kbps 15 msec 4.2

G.723.1 MPMLQ 6.3 kbps 37.5 msec 3.98

G.723.1 ACELP 5.3 kbps 37.5 msec 3.5

Initiator ◦ Encoding (DSP usage)

Transmit◦ Network transmit◦ Jitter Buffer

Receiver◦ Encoding (DSP usage)

ITU-T Codec Standard

Coding Scheme Used

Bit Rate Encoding Delay Time

Mean Opinion Score

G.711 PCM 64 kbps <1 msec 4.7

G.722 SB-ADPCM 64 kbps 4 msec 4.5 

G.726 ADPCM 32 kbps 1 msec 4.2

G.728 LC-CELP 16 kbps 2 msec 4.2

G.729 CS-ACELP 8 kbps 15 msec 4.2

G.723.1 MPMLQ 6.3 kbps 37.5 msec 3.98

G.723.1 ACELP 5.3 kbps 37.5 msec 3.5

VAD◦ Voice Activity Detection◦ “Clipping”

CNG◦ Comfort Noise Generation

PLC◦ Packet Loss Concealment

G.711A (a-law)G.711MU (m-law)G.722-64kG.722.1-24kG.722.1-32kG.723.1-5.3kG.723.1-6.3kG.726A-32kG.729G.729BG.729AB

SIREN14-24kSIREN14-32kSIREN14-48kSIREN14-S48kSIREN14-S56kSIREN14-S64kSIREN14-S96k

Human Hearing ◦ 5hz to 20khz

Narrowband Codecs◦ 200hz to 4khz

Wideband Codecs◦ 50hz to 7khz

G.xxx

e.g. G.722, G.711

Voice Encoding

H.xxx

e.g. H.323, H.264

Call Control

V.xxx

e.g. V.32, V.90

Modem Encoding

T.xxx

e.g. T.30, T.38

Fax Control

VoIP is not a conducive tofax or modem usage

Special settings◦ G.711 only ◦ Turns off VAD, CNG, PLC◦ Relay◦ Redundancy

Two codecs walk into a bar…