An efficient architecture for speech synthesis using Unit Selection Synthesis'

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An efficient architecture for speech synthesis
using Unit Selection Synthesis.

• CS422 Project Presentation
• Anil Muthineni
• Ashish Kumar Agarwal
• Atul Singh

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Speech Synthesis

• A very important branch of Natural Language
  Processing.
• Reads out things for us. E.g. Microsoft Narrator,
  Plain Talk, TalkIt,
• Essential component of bilingual computers so
  that a person in India can talk to a person with
  US without the help of any third person.
• Widespread usage in Railway announcement system,
  IVRS.
• Makes use of computer equally easy for blind
  people.

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Steps involved in Speech Synthesis
Normalization
Morphimization
Prosodization
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Basic Terminology and Techniques for Speech
Synthesis

• Text is first of all normalized.
• Then converted into phonetic transcriptions.
• Then divided into prosodic units.
• Then this linguistic representation is sent to
  the output unit.
• Then the output unit synthesizes the digital
  sound signals on the basis of this input signal.
• This output signal is fed to the last stage where
  it undergoes IQ and IDCT.

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Challenges

• Normal text is full of heteronyms, numbers and
  abbreviations.
• Entrance ??
• St. John St.
• 1234 1,234 1234
• in

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Major approaches for text to phoneme conversion

• Dictionary based
• Any token is searched in lexicon. If found the
  word is pronounced. Large Database required, very
  fast. Non dictionary words not possible.
• Syllable based
• Token is parsed into syllables using rules for
  pronunciation, each syllable is concatenated and
  converted into phoneme. Small Database required
  but slower. Not all words pronounced correctly.
  Put Cut !!

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Major approaches used for synthesis of sound

• Concatenative Synthesis Based on concatenation
  of segments of recorded speech. Can sometime
  produce audible glitches. Implement soft
  thresholding as a solution of this problem.
• Formant Synthesis Based on the synthesis of
  speech using frequency, amplitude and other
  characteristics of sound waveform.

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Requirement Analysis

• Because of the complexity of the algorithms
  involved, the processing cannot be done in real
  time on concurrent processors.
• A application specific instruction set processor
  provides the desired flexibility and
  enhancebility.
• Scalability with minimal changes is required.
• Naturalness and intelligibility are two essential
  components too.

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Requirement Analysis Contd.

• Need to minimize the glitches.
• For this we need to do things well in advance.
• Advance means advance on a nano-scale.
• For this we need to make the computing fast for
  that data which we get frequently.
• So this gives us the idea that the frequently
  used data needs to be stored in a cache time
  access memory.

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Requirement Analysis Contd.

• Also need to have well balanced pipelines.
• Because the time taken for text to morpheme
  conversion is almost half of the time taken in
  morpheme to sound conversion(Source Various
  Research Papers on Speech Synthesis)
• Basically due to bandwidth considerations.
• Increase the bandwidth or have two pipelines work
  to hide the latency.

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Concatenative Synthesis

• Unit Speech Synthesis Use of large recorded
  speech database created by segmentation of
  recorded utterance into syllables, phones,
  morphemes, words, phrases and sentences.
• Diphone Synthesis Uses minimal speech database
  containing only diphones.

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Implementation

• Unique Approach with novel ideas.
• Frequent things have been designed to be
  processed fast while things that occur rather
  infrequently, like symbols and numbers have been
  left out in the cold.
• Design is simplistic with least possible
  complexity.
• Power factor has been kept in mind with real time
  processing being the primary motive.

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Major features of the proposed architecture

• Two parallel pipelines, each with specialized
  tasks.
• Cache memory doesnt require to have a data cache
  because the data that we are dealing with is
  basically a stream in nature without any
  significant spatial locality.
• Besides the conventional cache, we will need one
  local storage which will have access time equal
  to that of cache that will be split into three
  parts
• First part will store the recently processed
  words in accordance with the principal of
  temporal and spatial locality
• Second part will store the database for all the
  frequently occurring morphemes
• Third will be a lookup table based built up on
  the basis of hashing algorithms which map a
  morpheme to its linguistic transcription. This
  minimizes the hard disk access.

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Pipelines

• One of the pipelines will convert the text into
  phonetic transcriptions.
• This will require lot of partitioning algorithms
  basically depending on loops and this code cannot
  be vectorized and hence this pipeline will have
  integer ALU with scalar registers.
• Meanwhile the other pipeline unit is processing
  the morpheme into linguistic unit.
• This pipeline has an SIMD FPU because of intense
  number crunching requirements.
• Care must be taken that the pipelines are
  interlocked.

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Block diagram of proposed architecture
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Cost and Performance Analysis

• As we have just shown, the processor has a very
  simple design.
• Done to minimize the hardware complexity
• Has two pronged benefits in terms of cost
• Less actual hardware resources
• Less control logic meaning less power
  expenditure.

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Contd

• Performance as such is bound to be good because
  the design is very straightforward.
• No quantitative result thus far because the idea
  is in its stage of infancy and has not been
  marketed so far.
• Yet intuitively, it is possible to conclude that
  the performance is going to be at least at par
  with that of the current commodity processors
  while doing general mathematic and scientific
  computations.

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Instruction Set Architecture

• Instruction set is small yet powerful with a
  variety of instructions.
• There are a couple of special purpose registers
  in addition to general purpose registers
• A status register has been kept to store
  information about pitch, intensity and
  speed/tempo.

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