Chapter 1 Flashcards
sound waves
pressure variations over time that are transmitted through a medium (usually air)
- We experience sound when air molecules are disturbed in the proximity of our auditory nerves and stimulate those nerves
- sound waves are mechanical waves
- sound waves are analog, or continuous
aperiodic waves
- transients
- noise
- aperiodic waves are those which do not have a repeating pattern (they are non-cyclic)
- spectra of aperiodic waves show many component frequencies
noise
the product of random air pressure variations
- frication is noise
- the waveform and spectrum of white noise appear the same
—spectra display a bunch of frequencies occurring at varying amplitudes
—the power spectrum can also look “flat” where its all the frequencies occurring at relatively the same amplitude
- aperiodic (non-cyclic)
transients
short, sharp pressure variations that are not maintained over time
- aperiodic (non-cyclic)
- waveform appear as a singular event (a singular spike in time)
- spectra appear as all frequencies occurring, but not randomly varying in amplitude (as in noise)
- oral stop releases are transients
fundamental period
the time interval in which each cycle of a sound wave repeats
- the time between vocal fold closure/opening during voicing
fundamental frequency
The fundamental frequency (f0) is the lowest component frequency of a complex periodic wave.
—the frequency of the longest repeating pattern of a complex periodic wave
—also equal to the first harmonic (H1)
How do you calculate frequency from period (and vice-versa)?
period (T) = 1/f
—units for T is seconds
frequency (f) = 1/T Hz
—units for f is Hz
complex periodic waves
sound waves composed of a sum of multiple component sine waves
- complex periodic waveforms do not appear as sine waves (they do not have a singular frequency)
Fourier Theorem
The idea that complex periodic waves are composed of sine waves of varying frequencies and amplitudes. In other words, the idea that sine waves add together to form a complex periodic wave
What are the components of a spectral display of frequency?
A spectrum displays the component frequencies of a sound sample at what (relative) amplitude they occur at
- horizontal axis: frequency
- vertical axis: amplitude
- spectra of sine waves will display a singular component frequency
waveforms vs. spectra vs. spectrograms
-
waveforms: x: time, y: amplitude
—Show the amplitude of a sound sample over time
—frequency is not directly displayed, but can be calculated by identifying the period of the wave -
spectra: x: frequency, y: amplitude
—show the component frequencies of a snapshot sound sample and at what relative amplitude they occur at
—do not display time whatsoever (are a snapshot) -
spectrograms:
—3 dimensions: x: time, y: frequency, darkness: amplitude
How do we perceive different aspects of a sound wave?
- amplitude = loudness
—higher amplitude = higher volume - frequency = pitch
—higher frequency = higher pitch
frequency and amplitude are independent
—fundamental frequency (f0): the pitch of the voice
sine waves vs. complex periodic waves
Sine waves are periodic/cyclic and represent sounds with only one frequency. Samples of the human voice are not sine waves, but complex periodic waves.
Complex periodic waves are also periodic, but they are the sum of multiple sine waves (multiple frequencies).
Fourier synthesis vs. Fourier analysis
Fourier synthesis is the act of adding (synthesizing) individual sine waves together to form a complex periodic wave.
Fourier analysis is the act of decomposing (analysing) a complex periodic wave such that it is broken down into its component sine waves.
4 components of acoustic energy in speech
-
voicing
—complex periodic signal -
frication (noise)
—aperiodic -
aspiration (noise)
—aperiodic -
transients
—aperiodic
What is the fundamental frequency with respect to voicing?
The fundamental frequency (f0) is the frequency of vocal fold vibration, and what we interpret as pitch.
frication
noise generated in the vocal tract due to turbulent airflow
- voiced fricatives will show glottal pulses on the spectrogram, whereas voiceless fricatives will show no vertical lines
aspiration
noise generated in the glottis
- voiceless fricatives may have simultaneous aspiration noise due to airflow through the glottis
rarefaction
with respect to sound waves, the decrease in pressure along a sound wave/between air particles
- pressure = “crowdedness” of particles
- rarefaction is the opposite of compression
compression
with respect to sound waves, the increase in pressure along a sound wave/between air particles
- pressure = “crowdedness” of particles
- compression is the opposite of rarefaction
impulse
a sudden, sharp sound that is not maintained
- naturally occurring, spontaneous transients will show the same sound signal as an impulse
- impulses on a waveform show that there is only one point in time where the sound amplitude increases, and on a power spectrum show a straight line at a fixed amplitude
