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RMAUG Professional Development Series 2/11/09 Dwight Reifsnyder.

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Presentation on theme: "RMAUG Professional Development Series 2/11/09 Dwight Reifsnyder."— Presentation transcript:

1 RMAUG Professional Development Series 2/11/09 Dwight Reifsnyder

2 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

3 Boulder Valley School District

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

5  Codec is short for Coder/Decoder  Just like a Dick Tracy!  But what are the concepts involved?

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

7  1876 Alexander Graham Bell ◦ Audio to electricity  1894 Guglielmo Marconi ◦ Audio to radio  1916 Theodore Case ◦ Audio to optical

8  An analog or analogue signal is 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

9  Alec H. Reeves ◦ Pulse Code Modulation invented (PCM)  John V. Atanasoff, Clifford Berry ◦ First computer  1962 – Bell Labs ◦ PCM first used in commercial telephony

10  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.

11  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.

12  Analog ◦ Continuous, modulates in direct relation to original data  Digital ◦ Discrete data (individual values) with no intuitive or obvious correlation to original data

13  Encoding is changing form. Data may be encoded, transmitted, stored, and decoded  Analog (encoding or transmission)  Digital (encoding or transmission)

14 TIF (TIFF) Tagged Image File Format PNG Portable Network Graphic GIF Graphics Interchange Format JPG (JPEG) Joint Photographic Experts Group

15 TIF (TIFF) 576K No Compression (lossless) PNG 232K No Compression (lossless) GIF 97K Compressed (lossy) JPG (JPEG) 105K Compressed (lossy)

16  If the pictures all look the same, why do we need different Codecs?  Different types of Codecs are optimized for different types of data

17  GIF uses Run Length Encoding (RLE) AAAABBBBBCCCCDDDDDDEEEEEEEE 4A4B4C6D8E  Max of 256 colors, fewer colors=smaller file

18  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 = | | | | | | | | | | | | | |

19 JPG (JPEG) Quality “100” 105k JPG (JPEG) Quality “30” – 16K

20 GIF 256 Colors (lossless) 97k GIF 32 Colors (lossy) 17K

21  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

22  There a many audio codecs ◦ Quicktime ◦ Real Player ◦ MP3  Voice Specific Codecs ◦ Industry Standard (ITU) ◦ Optimized for speech

23 ITU-T Codec Standard Coding Scheme Used Bit RateEncoding Delay Time Mean Opinion Score G.711PCM64 kbps<1 msec4.7 G.722SB-ADPCM64 kbps4 msec4.5 G.726ADPCM32 kbps1 msec4.2 G.728LC-CELP16 kbps2 msec4.2 G.729CS-ACELP8 kbps15 msec4.2 G.723.1MPMLQ6.3 kbps37.5 msec3.98 G.723.1ACELP5.3 kbps37.5 msec3.5

24  For most users, the main consideration in choosing a codec is bandwidth  This can be complex when considering calls between multiple regions

25

26 ITU-T Codec Standard Coding Scheme Used Bit RateEncoding Delay Time Mean Opinion Score G.711PCM64 kbps<1 msec4.7 G.722SB-ADPCM64 kbps4 msec4.5 G.726ADPCM32 kbps1 msec4.2 G.728LC-CELP16 kbps2 msec4.2 G.729CS-ACELP8 kbps15 msec4.2 G.723.1MPMLQ6.3 kbps37.5 msec3.98 G.723.1ACELP5.3 kbps37.5 msec3.5

27  Initiator ◦ Encoding (DSP usage)  Transmit ◦ Network transmit ◦ Jitter Buffer  Receiver ◦ Encoding (DSP usage)

28

29 ITU-T Codec Standard Coding Scheme Used Bit RateEncoding Delay Time Mean Opinion Score G.711PCM64 kbps<1 msec4.7 G.722SB-ADPCM64 kbps4 msec4.5 G.726ADPCM32 kbps1 msec4.2 G.728LC-CELP16 kbps2 msec4.2 G.729CS-ACELP8 kbps15 msec4.2 G.723.1MPMLQ6.3 kbps37.5 msec3.98 G.723.1ACELP5.3 kbps37.5 msec3.5

30  VAD ◦ Voice Activity Detection ◦ “Clipping”  CNG ◦ Comfort Noise Generation  PLC ◦ Packet Loss Concealment

31 G.711A (a-law) G.711MU (m-law) G k G k G k G k G k G.726A-32k G.729 G.729B G.729AB SIREN14-24k SIREN14-32k SIREN14-48k SIREN14-S48k SIREN14-S56k SIREN14-S64k SIREN14-S96k

32  Human Hearing ◦ 5hz to 20khz  Narrowband Codecs ◦ 200hz to 4khz  Wideband Codecs ◦ 50hz to 7khz

33 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

34  VoIP is not a conducive to fax or modem usage  Special settings ◦ G.711 only ◦ Turns off VAD, CNG, PLC ◦ Relay ◦ Redundancy

35  Two codecs walk into a bar…


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