Basic Spectrogram Lab 8. Spectrograms §Spectrograph: Produces visible patterns of acoustic energy...
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Transcript of Basic Spectrogram Lab 8. Spectrograms §Spectrograph: Produces visible patterns of acoustic energy...
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
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
Dimensions of SpectrogramsA. Burst of noise B. Vowel with 4 formants
C. Noise with high frequency energyTime
Source/FilterResonator & 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)
Formants- Filter
Are formed through resonation of sound in the vocal tract (filter function)
Can only see through a wide band spectrogram
F1F2F2
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
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
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)
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?
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