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45 Cards in this Set
- Front
- Back
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"Sound is the sensation you experience when...
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your auditory nerves are stimulated by vibrating air molecules."
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sound waves
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pressure variations over time in the air, transmitted by movements of air molecues
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digitizing
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converting sound from analog (continuous) to digital (discrete) (analog-to-digital = A/D)
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sampling interval
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at what time interval T are points sampled from the signal (e.g. every millisecond)
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Hertz (Hz)
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cycles per second
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f (in Hz) =
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1000 / T (in ms)
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quantization
(resolution) |
"sampling" of amplitude
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quantization rate
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the number of bits for encoding that number of values (8, 12, or 16 bits are common)
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clipping
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when the peak amplitude of the sample is greater than the largest amplitude allowed by quantization
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Nyquist frequency
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twice the desired signal frequency (necessary to sample at this for good quality)
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the critical information in speech is from about...
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100-5000Hz
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CD digital audio has...
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SR: 44,100 Hz
QR: 16 bits |
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WAV files
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SR: any
QR: 16 or 32 bit -uncompressed! |
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MP3
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SR: almost always 44,100Hz
QR: varies a lot -compressed! |
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Are digital signals ever continuous?
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never!
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amplitude
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maximum displacements
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waveforms
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vertical axis is amplitude and horizontal axis is time
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frequency
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cycles per second
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period
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duration of one cycle
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T=
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duration of one cycle
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frequency is heard as
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pitch
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amplitude is heard as
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loudness
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complex waves
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the sum of multiple sine waves
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Fourier theorem
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complex periodic waves are composed of sine waves of varying frequencies and amplitudes
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Fourier synthesis
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add sine waves together to get a complex wave
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Fourier analysis
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decompose a complex wave into sine waves
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fundamental frequency (F0)
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the lowest component frequency of a complex periodic wave
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spectrum
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-a picture (static, of a single moment in time) of the component frequencies, and their relative amplitudes
-horizontal axis is frequency, vertical is amplitude |
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line spectrum
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idealized, each component is a vertical line
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the spectrum of a sine wave shows...
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a single component frequency
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aperiodic sounds
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not cyclic, no repeating patterns, spectrum has many component frequencies; white noise
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transient
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short, sharp pulse; not periodic; (waveform: pulse, spectrum: al frequencies)
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spectrogram
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horizontal axis is time and vertical axis is frequency, amplitude is shown as darkness of the frequencies
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4 sources of acoustic energy in speech
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-voicing
-frication -aspiration -transients |
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voiced speech is a complex periodic signal composed of...
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fundamental frequency (heard as pitch) and higher frequency components
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voice source
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voicing as a source of acoustic energy
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vertical lines in spectrograms show...
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voice source pulses (cycles of vocal old opening and closing)
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2 sources of fricatives
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voice source and frication source
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filter
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pass or blocks different frequencies
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affricate
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transient plus frication
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hearing range
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15-20,000 Hz
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resonance
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kind of sympathetic vibration, gives formants more energy
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formant (formant frequencies)
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resonances of the vocal tract
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F1
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height (inversely)
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F2
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frontness (higher=fronter)
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