EE2F1 Speech

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EE2F1Speech Audio TechnologyMartin
RussellElectronic, Electrical Computer
EngineeringSchool of EngineeringThe University
of Birmingham
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Speech Audio Technology

• Lectures Tuesdays, 10am LT1
• Two laboratory sessions
• NG22, Thursday/Friday 2pm-5pm
• Week 6 introduction to SFS
• Week 8 speech synthesis
• Check timetable for groups
• Examination next semester
• Revision lecture next semester
• Follow-on course EE2F2 Music Technology by Dr T
  Collins

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Demonstrations

• Time-domain and Frequency-domain representations
  of sounds
• Time-domain waveform or signal
• Frequency domain spectrum
• Time-frequency representation spectrogram
• Tools
• Sound Forge XP 4.5 (Commercial software)
• SFS (Speech Filing System) 4.28 for windows
• SFS is free! http//www.phon.ac.uk/resource/sfs

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Sine wave 880Hz
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Recorder A (880Hz)
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Piano middle C, 8ve, 2x8ve
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Saxophone
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Voice plus background drone
Kate Rusby, Annan Water from Hourglass Pure
records 1997
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Rock Music
Bruce Springsteen, Born in the USA, Columbia 1984
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Electronic music
Moby, Porcelain, Mute Records 1999
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Analogue-to-Digital Conversion

• A/D conversion
• or Sampling
• or Digitization

PC Sound Card
D/A converter
Amplifier
Disk
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Pulse Code Modulation (PCM)
Quantization error
Sample point
Quantization point

• How many quantization points?
• How many samples per second (sample rate)?

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Nyquists Theorem

• (Ignore quantization error for now)
• Suppose a signal has no frequency components
  above B Hz
• If that signal is sampled 2B times per second,
  then it can be faithfully reconstructed from the
  digital signal
• B is called the Nyquist frequency
• 2B is called the Nyquist rate
• Reconstructing the original signal from the
  digital signal is called Digital-to-Analogue (or
  D/A) conversion

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Aliasing

• Aliasing happens when a signal is sampled at a
  rate less than the Nyquist rate
• Detail is lost in the reconstruction of the
  signal
• Spurious low-frequency components appear in the
  reconstructed signal
• These are aliases of real components of the
  signal
• Example

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Aliasing
Reconstructed alias
Less than Nyquist rate
Nyquist rate
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Analogue-to-Digital Conversion

• For a given sampling rate, an anti-aliasing
  filter removes all frequency values above the
  Nyquist frequency

PC Sound Card
Anti-aliasing filter
D/A converter
Amp
Disk