Basic Spectrogram Lab 8

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Basic SpectrogramLab 8
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Spectrograms

• Spectrograph Produces visible patterns of
  acoustic energy called spectrograms
• Spectrographic Analysis
• Acoustic signal changes rapidly continuously
• Need a dynamic analysis revealing spectral
  features
• Short term running spectrum

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Spectrographic Analysis

• Time, Frequency intensity
• Time (horizontal axis) Phonetic elements will be
  from left to right
• Frequency (Vertical axis) Increasing in upward
  direction
• Intensity represented by a gray scale or as
  variations in darkness

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Dimensions of Spectrograms
A. Burst of noise
B. Vowel with 4 formants
Time
C. Noise with high frequency energy
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Source/Filter

• Resonator Source Energy
• Filter Vocal tract
• Energy passed in a frequency selective manner
• Production of different vowels changes the filter
  shape
• Source Harmonic spectrum of voicing
• Fundamental frequency its harmonics
• Source spectrum is the acoustic energy activating
  the formants
• Source-filter theory of vowel production
• The energy form the source (vibrating vocal
  folds) is modified by the resonance
  characteristics of the filter (vocal tract)

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Formants- Filter

• Are formed through resonation of sound in the
  vocal tract (filter function)
• Can only see through a wide band spectrogram

F2
F2
F1
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Harmonics- Source
Harmonics (Spectrum)
Harmonics(Spectrogram)
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Source-Filter Theory
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Source-Filter
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Wide Band vs. Narrow Band

• Wide Band analyzing filter wide, 300-400 Hz
• Good to show formants because they have a wide
  spread of acoustic energy
• Narrow Band analyzing filter is of higher
  resolution, 100 Hz
• Good to show the harmonics of source spectrum

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Bandwidth
Narrow Bandwidth (Harmonics)
Wide Bandwidth (Formants)
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Continuous Spectrum Bandwidth
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Vowel Wide Band vs. Narrow Band
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Wide Band Spectrogram
Fricative noise Above 3 or 4 kHz
Diphthong Horizontal bands of energy
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Digital Signal Processing

• Basic objective of digital signal processing
• Convert the analog acoustic signal (Panel A) to a
  digital form (series of s)
• How do we get a waveform into a digital computer?
• Analog-Digital conversion (A-D) results in
  samples of time and amplitude
• Correct sampling rate is important to reconstruct
  the wave form
• Sampling rate must be 2x the bandwidth of
  analysis Nyquist Frequency
• Ex. Sample speech with a bandwidth of 5000 Hz,
  than the sampling rate should be 10,000 Hz

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Analog-Digital Conversion
b. Time sampling intervals
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Laboratory

• Part I Recording the sample- Sampling rate
• Set sampling rate for shortest duration possible
• Sustain /a/ open 3 views to print all samples
  on 1 screen
• Sample at 20,000 samples/sec look at 5-6 cycles
• Sample at 5,000 samples/sec look at 5-6 cycles
• Sample at 2,500 samples/sec look at 5-6 cycles
• What happens as sampling rate drops
• Narrow band filter each sample (print each)

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Laboratory

• Part II Filter bandwidth
• Record I am tall
• Wide band and narrow band the statement
• Find the following characteristics on one or both
  of the spectrograms
• Harmonic lines
• Formant bands
• Vertical striations
• Acoustic indication of release of air pressure
  for /t/
• Which has better frequency resolution? Time
  resolution? Which can you determine formant bands?

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Laboratory

• Part II Cont.
• Make wide and narrow band spectrograms of the
  following, stressing the underlined word
• I am tall
• I am tall
• I am tall
• I am tall?
• Which spectrograms show the intonation contour?
  Mark the contour on one of your printouts

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Laboratory

• Part III Changing the Filter
• Say /iui/ without changing intonation
• Prepare 2 spectrograms of this utterance
• 1st- 2xs your fundamental frequency
• 2nd- no more than half your fundamental
• Answer questions
• Label each vowel on each spectrogram
• Harmonics
• Formants