Section 3 Flashcards
What are complex waves?
Characterized by a combination of different frequencies, amplitudes, and phase relationships. Can be periodic or aperiodic.
What does periodic mean?
Wave repeats over time and has a musical or tonal quality (musical notes, sustained vowels in speech)
What does aperiodic mean?
Wave does not repeat itself over time and has more of a “noise” type quality (transient sounds in speech and environment)
How do frequencies work in a periodic complex sound?
All frequencies are whole number multiples of the fundamental frequency (harmonic series)
What is the fundamental frequency?
the lowest frequency of vibration in a harmonic series
Explain harmonics
Any whole number multiple of the fundamental frequency
How does the fundamental frequency relate to the first harmonic?
They are the same number, since the fundamental frequency can be multiplied by itself.
How do you find the second harmonic?
The second harmonic is twice the fundamental, the third three times the fundamental, the fourth four times the fundamental, etc.
What is an overtone?
Any component in a complex tone having a frequency higher than the fundamental- the first overtone is equal to the second harmonic, etc.
What is a partial?
Indicates a part of partial of the complex tone or harmonic series- the fundamental frequency is also the first partial
What is an octave?
Any interval of two frequencies having a frequency ration of 2:1 (a doubling of the frequency)
Do harmonics all have equal amplitudes?
No, even though fundamental frequency determines all harmonic frequencies.
What is the result of two waves of different frequency and/or amplitude being generated simultaneously?
A new wave that is the sum of each of the separate waves.
What is a steady state sound?
Frequency, composition, amplitude and phase relationship of the partials of a tone are constant over time- usually periodic.
What is a transient sound?
A change in steady state- usually aperiodic.
What is a Fourier analysis? How is it represented? What is on this representation?
Shows that any complex sound can be broken down to show the individual sinusoidal components of that sound. Represented on a graph called a spectrum that shows the amplitude, frequency, and phase of each individual sine wave in a complex sound.
What is an amplitude spectrum?
The ordinate will indicate the range of amplitudes, the abcissa will indicate the range of frequencies
What is a phase spectrum?
Can also be plotted to show the starting phase of each individual sine wave
What does each line on a spectrum represent?
An individual sine wave that is part of the complex sound (therefore the line will inherently represent the individual sine waves amplitude, frequency, and phase.
What is interference?
The phenomenon that occurs when two waves meet while traveling along the same medium. The interference of waves causes the medium to take on a shape that results form the net effect of the two individual waves.
What is constructive interference?
A type of interference where two interfering waves have a displacement in the same direction. Can occur where the two interfering waves are displaced upwards, or when they are displaced downward.
What occurs when two interfering waves are in phase? (Started at the same phase and were identical in amplitude and frequency)
Would result in summation of the two waves and a doubling. Ex: If a sine wave with a max displacement of -1 interferes with a sine wave with the same frequency with a max displacement of -1 unit, the the resulting wave in the medium is a sine wave with a max displacement of -2 units.
What is destructive interference?
Where two interfering waves have displacement in opposite directions. If a sine wave with a max displacement of +1 meets with a sine wave of -2, then the resulting displacement will be -1. If two interfering waves of the same frequency and amplitude meet but are 180 degrees out of phase, the waves will cancel each other out- resulting in no sound.
Explain what a beat is
When two sound waves of almost identical frequency combine, the alternating constructive and destructive interference causes the sound to be alternatively soft and loud- sounding like it is “beating.”
What is “noise”
Noise is a sound that has little or no periodicity- a sound with instantaneous amplitude that varies over time in a random manner.
What is white noise?
All frequencies in a a specific range are present, regardless of phase, and the average power over a frequency range is constant. Average power is equal to the product of the frequency range and intensity.
What is pink noise?
Amplitude decreases by one half with each doubling of frequency
What is a low pass filter?
Attenuates high frequencies and passes low frequencies
What is a high pass filter?
Attenuates low frequencies and passes high frequencies
What is a combination filter?
A combination of a low and a high pass filter to pass a specific range of frequencies (narrow band or speech noise)
What is a transient sound?
Speech, that is not steady, is a series of transient sounds. Transient sounds are aperiodic and change frequently.
How did white noise get it’s name?
White noise gets it’s name from white light. All frequencies within a specific range are present regardless of the phase and all the intensities are the same. There will be single line at each frequency when looking at the spectrum.
What is an ordinate on a spectrum?
Refers to an element plotted on the vertical axis and tells us the amplitude/intensity of sound
What is an abcissa on a spectrum?
The horizontal axis of a spectrum, tells us the time.
How common are pure tones? What are most sounds?
Not common in nature at all, usually complex sounds
