0. Sharif University of Technology
Speech Coding Basics
A Tutorial
Mahdi Amiri
Supervisor
Dr. H. R. Rabiee
April 2009
Sharif University of Technology

1. Speech Coding PCM DPCM ADPCM LPC CELP A road map Page 1 of 30
Speech Coding Basics

2. Pulse-code Modulation (PCM)
Basics
Digital Representation of an Analog Signal
Sampling and Quantization
Parameters:
Sampling Rate (Samples per Second)
Quantization Levels (Bits per Sample)
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Speech Coding Basics

3. Pulse-code Modulation (PCM)
Why Call it PCM?
4-bit PCM
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Speech Coding Basics

4. Pulse-code Modulation (PCM)
Bit per Second (bit/s)
How to choose proper…
Sampling Rate
8 Khz ?
Quantization Level
8 bit/sample ?
Bit per Second for 8000 Hz 8 bit PCM
64 kbit/s
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Speech Coding Basics

5. Pulse-code Modulation (PCM)
Sampling Rate
Human Hearing Frequency Range
20 Hz to 20 kHz
Play with “HearTest” to test your hearing
Most people will find that their hearing is most sensitive around 1-4 kHz and that it is less sensitive at high and low frequencies.
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Speech Coding Basics

6. Pulse-code Modulation (PCM)
Hearing Range
Ferret = Persian: Raasoo
GERBIL = Persian: Moosh Sahraaiee
Hedgehog = Persian: Joojeh Tighi
Possom = Like Opossums : Persian: Saarigh
Seal = Persian: Fok
Porpoise = Persian: Khook Daryaayee (Shabihe dolphin va nahang)
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Speech Coding Basics

7. Pulse-code Modulation (PCM)
Sampling Rate
Human Vocal Range
Normal: 80 Hz to 1100 Hz
Charles Kellogg (14 KHz) (not verified)
Guinness Book of Records
Female: Georgia Brown
(Eight octaves, 25087Hz)
Male: Tim Storms
(Six octaves)
Georgia Brown's High Notes
Georgia Brown incredibly screams the high notes that made her the woman with the largest vocal range on the planet
Tim Storms Sings Eight Hertz
Tim storms demonstrates his low range. He sings so low you can't even hear it.
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Speech Coding Basics

8. Pulse-code Modulation (PCM)
Common Sampling Rates
8,000 Hz: Telephone, adequate for human speech
11,025 Hz
22,050 Hz – radio
32,000 Hz - miniDV digital video camcorder, DAT (LP mode)
44,100 Hz - audio CD, also most commonly used with MPEG-1 audio (VCD, SVCD, MP3)
48,000 Hz - digital sound used for miniDV, digital TV, DVD, DAT, films and professional audio
96,000 or 192,000 Hz - DVD-Audio, some LPCM DVD tracks, BD-ROM (Blu-ray Disc) audio tracks, and HD-DVD (High-Definition DVD) audio tracks
MHz - SACD, 1-bit sigma-delta modulation process known as Direct Stream Digital, co-developed by Sony and Philips”
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Speech Coding Basics

9. Pulse-code Modulation (PCM)
Quantization Levels
Want to prevent human ear fatigue by minimizing quantization noise
Signal-to-Noise Ratio = 6.02B dB
SNR is approximately 6 dB per bit.
16-bit => 96 dB
Above 36 dB is required
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Speech Coding Basics

10. Pulse-code Modulation (PCM)
Good to Know
The average person cannot tell the difference between a bitrate above 192 kbit/s and the original CD/WAV.
Even if your headphones seal really well around your ears, they will probably only give you about 20 to 25 dB insulation from the external sound.
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Speech Coding Basics

11. Pulse-code Modulation (PCM)
Images
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Speech Coding Basics

12. Pulse-code Modulation (PCM)
u-law, a-law
Nonuniform quantizers: Difficult to make, Expensive.
Solution: Companding  Uniform Q.  Expanding
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Speech Coding Basics

13. Pulse-code Modulation (PCM)
U-law, A-law
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Speech Coding Basics

14. Pulse-code Modulation (PCM)
u-law, a-law
North America and Japan
Europe
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Speech Coding Basics

15. Differential PCM (DPCM)
Idea
Unfortunately, this does not work on analog sources since dn != dn^ , and
thus Pn != Pn^. Leads to error accumulation!
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Speech Coding Basics

16. Differential PCM (DPCM)
Basic Scheme
General Predictive Coding
Problem?
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Speech Coding Basics

17. Differential PCM (DPCM)
Better Structure
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Speech Coding Basics

18. Adaptive DPCM (ADPCM) Idea Problem? Page 18 of 30 Speech Coding Basics
Unfortunately, this does not work on analog sources since dn != dn^ , and
thus Pn != Pn^. Leads to error accumulation!
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Speech Coding Basics

19. Adaptive DPCM (ADPCM) Size of Quantization Step Page 19 of 30
Speech Coding Basics

20. Speech Compression Concepts
Spectrogram, STFT
3D surface spectrogram of a part from a music piece.
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Speech Coding Basics

21. Speech Compression Concepts
Spectrogram
Spectrogram of a male voice saying ‘nineteenth century’.
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Speech Coding Basics

22. Speech Compression Concepts
Spectrogram, Demonstration
Bat Echolocation Call
Flute by Jean Pierre Rampal
Face!
Singing Voice
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Speech Coding Basics

23. Speech Compression Concepts
Formant
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Speech Coding Basics

24. Linear Predictive Coding (LPC)
Modeling
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Speech Coding Basics

25. Linear Predictive Coding (LPC)
Modeling (Hiss or Buzz)
Buzzer  Filter
Chuncks: 30 thr. 50 frames/sec.
Speech = Formants + Residue
Predictor for each frame:
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Speech Coding Basics

26. Linear Predictive Coding (LPC)
Modeling (Hiss or Buzz)
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Speech Coding Basics

27. Code Excited Linear Prediction
CELP
Problem of LPC
Where there is both Hiss and Buzz
Solution
Encode residue
Method
Vector Quantization (Codebook)
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Speech Coding Basics

28. Comparison Sample Speech
A lathe is a big tool. Grab every dish of sugar.
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Speech Coding Basics

29. Comparison Demonstration Original ADPCM LPC CELP Page 29 of 30
Speech Coding Basics

30. Thank You Speech Coding Basics A Tutorial
FIND OUT MORE AT... 1. 2.
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Speech Coding Basics

31. Animated Title
Title
Abc
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Speech Coding Basics

32. Definition of Vanishing Percentage (VP)
Title
Title
Abc
Definition of Vanishing Percentage (VP)
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Speech Coding Basics