Digital Signal Processing:An Introduction and Some Examples of its
Everyday Use
Dr D. H. Crawford
EPSON Scotland Design Centre
Slide 2
Contents
• What is DSP?
• What is DSP used for?– Speech & Audio processing– Image & Video processing– Adaptive filtering
• DSP Devices and Architectures
• DSP at EPSON Scotland Design Centre
• Summary & Conclusions
Slide 3
What is DSP?
• Digital Signal Processing – the processing or manipulation of signals using digital techniques
ADC DACDigital Signal
ProcessorAnalogue to Digital Converter
Digital to Analogue Converter
Input Signal
Output Signal
Slide 4
What is DSP Used For?
……And much more!And much more!
Slide 5
Speech Processing
• Speech coding/compression
• Speech synthesis
• Speech recognition
Slide 6
Some Properties of Speech
The blue--- s---p--o---------t i-s--on--the-- k--ey a---g--ai----n------
“oo” in “blue”“o” in “spot”“ee” in “key”“e” in “again”“s” in “spot”“k” in “key”
Slide 7
Some Properties of Speech
“ee” in “key”“o” in “spot”“oo” in “blue” “e” in “again”
Vowels
“s” in “spot” “k” in “key”
Consonants
•Quasi-periodic
•Relatively high signal power
•Non-periodic (random)
•Relatively low signal power
Slide 8
Speech Coding
BTS
BSC
MSC
TRAU
64 kbits/s
13 kbits/s
22.8 kbits/s
Slide 9
Speech Coding – Linear Prediction
A(z)
s(n)+
– d(n)
se(n)… d(n)
A(z)
++
se(n)
sr(n)
• Try to predict the current sample value;
• Transmit the prediction error.
Slide 10
Speech Coding – Vocoder
G
Pulse Train
Random Noise
Vocal TractModel
V/U
Synthesized Speech
Decoder
Original Speech
Analysis:• Voiced/Unvoiced decision• Pitch Period (voiced only)• Signal power (Gain)
Signal PowerPitch
Period
Encoder
LPC-10:
Slide 11
To be ornot to bethat is thequestion
Textnormalization
expandsabbreviationsdates, times,money..etc
Parsing Pronunciation
Prosodyrules
Tu bee awrnawt tu beedhat iz dhekwestchun
semantic &syntactic ‘partsof speech’ analysis of text
phonetic descriptionof each word, dictionarywith letter-to-sound rules as a back up
Waveformgeneration
Synthesized speech
Apply wordstress, durationand pitch
Phonetic-to-acoustictransformation
phonetic formInputtext
Text-to-Speech Synthesis
Text-to-speech synthesis sounds very natural these days.
Slide 12
Speech Synthesis Applications
• Speaking clocks
• Spoken (variable) announcements
• Talking emails + talking heads for mobile
• Synthesis of location-based information (e.g. traffic information)
• Interactive systems (e.g. catalogue ordering, Yellow Pages, ...)
Slide 13
Speech/Speaker Recognition• Speech Recognition – What has been spoken?
– Speaker dependent – Recognition system trained for a particular person’s voice.
– Speaker independent – Recognition system expected to deal with a wide variety of speakers.
• Speaker Recognition – Who has spoken?
• Not easy…Sometimestherearenogapsbetweenwords.Sometim esthereareg aps inthe mid dleofwords.
Accents, dialects and Stress eggsist.
Slide 14
Speech Recognition System
Featureextractionspeech
Phoneme recognition
Phonememodels
Sentencerecognition
Wordrecognition
Word pronunciation
Semantic knowledge
decision
Syntactic knowledge
Dialogue knowledge
Slide 15
Digital Audio
• Standard music CD:– Sampling Rate: 44.1 kHz– 16-bit samples– 2-channel stereo– Data transfer rate = 21644,100 = 1.4 Mbits/s– 1 hour of music = 1.43,600 = 635 MB
Slide 16
Audio Coding (Cont’d)
• Key standards:– MPEG: Layers I, II, and III (MP3); AAC.
• used in DAB, DVD
– Dolby AC3, Dolby Digital, Dolby Surround.
• Typical bit rates for 2-channel stereo:– 64kbits/s to 384 kbits/s.
• Subband- or transform-based, making use of perceptual masking properties.
Slide 17
Audio Coding (Cont’d)
• 5.1 channels (3/2) with LFE channel:– Left, Right, Centre,– Left Surround, Right Surround,– Low Frequency Effects (LFE) (Reduced Bandwidth).
• LFE loudspeaker can, in general, be placed anywhere in the listening room.
• Typical 3/2 multichannel stereo configuration:
RightSurround
Right
Surround Left
Centre
Left
Slide 18
Audio Coding – Masking
• Auditory Masking:– Spectral: Strong frequency components mask weaker
neighbouring frequency components.
– Temporal: Strong temporal events mask recent and future events.
SPL/dB
10ms 160ms
Temporal Masking
timefreq/kHz1
SPL/dB
Spectral Masking
Slide 19
200 300 400 500 600 700 800
10
20
30
40
50
60
Hz
dB
Masking Example
Slide 20
Image/Video
• Still Image Coding:– JPEG (Joint Photographic Experts Group):
• Discrete Cosine Transform (DCT) based
– JPEG2000: Wavelet Transform based
• Video Coding:– MPEG (Moving Pictures Experts Group):
• DCT-based,
• Interframe and intraframe prediction,
• Motion estimation.
– Applications: Digital TV, DVD, etc.
Slide 21
JPEG ExampleOriginal
JPEG (100:1)JPEG (4:1)
Slide 22
Adaptive Filtering
• Self-learning: Filter coefficients adapt in response to training signal.
W(z) +
–x(n)y(n)
e(n)
d(n)
)()(2)()1( nnenn xww
• Filter update: Least Mean Squares (LMS) algorithm
Slide 23
Adaptive Filtering Applications
• Echo cancellation (telephone lines)– Used in modems (making Internet access possible!!)
• Acoustic echo cancellation– Hands-free telephony
• Adaptive equalization• Active noise control• Medical signal processing
– e.g. foetal heart beat monitoring
Slide 24
Some Other Application Areas
• Image analysis, e.g:– Face recognition,– Optical Character Recognition (OCR);
• Restoration of old image, video, and audio signals;• Analysis of RADAR data;• Analysis of SONAR data;• Data transmission (modems, radio, echo
cancellation, channel equalization, etc.);• Storage and archiving;• Control of electric motors.
Slide 25
DSP Devices & Architectures
• Selecting a DSP – several choices:– Fixed-point;
– Floating point;
– Application-specific devices(e.g. FFT processors, speech recognizers,etc.).
• Main DSP Manufacturers:– Texas Instruments (http://www.ti.com)
– Motorola (http://www.motorola.com)
– Analog Devices (http://www.analog.com)
Slide 26
Typical DSP Operations
• Filtering
• Energy of Signal
• Frequency transforms
1
0
)()(L
ii inxany
for (n=0; n<N; n++){ s=0; for (i=0; i<L; i++) { s += a[i] * x[n-i]; } y[n] = s;}
Pseudo C code
Slide 27
Traditional DSP Architecture
X RAM Y RAM
Multiply/Accumulate
Accumulator
x(n-i) ai
y(n)
N.B. Most modern DSPs have more advanced features.
Slide 28
DSP at EPSON
EPSON Scotland Design Centre develops a broad range of technologies to minimize power consumption and maximize cost
effectiveness in mobile DSP applications.
“Energy-saving Firmware”
Slide 29
SDC Core Skills
System Integration
System modelling
DSP
Speech Testing
Speech enhancement
Speech synthesis
Speech Recognition
Speech
PerformanceAssessment
MP3
Audio
Channel coding
Baseband processing
Mobile
Computer &
Networking
CAD Tools
Administration
Services
System on Chip (SoC)
Firmware design
AMR Coding
Speech compression
CPU (Oak, ARM)
H/w & S/w Co-design
Other digital audio
Slide 30
SDC Firmware DevelopmentAlgorithm Definition
Floating-point and
Fixed-pointCo-Simulation
Co-Design
Implementation Co-Verification
COSSAPMatlab ...
Product Development
Behavioural, RTL, Logic ...
With Barcelona and TokyoDesign Centres
MCU, DSP ...
Slide 31
Summary & Conclusions
• DSP used in a wide range of everyday applications• Looked at:
– Speech coding; Speech synthesis & recognition;
– Image/Video;
– Adaptive filtering.
• Other areas include:– Image analysis (e.g. face recognition, OCR, etc.);
– RADAR/SONAR;
– Data transmission and reception;
– And many more…..!!
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