Sound & Music Theory
Introduction to timbre, pitch, sine waves, etc.
61 flashcards · Physics · by lakesare
What is AM vs FM?
Amplitude modulation: The amplitude of the carrier wave varies proportionally according to the input signal, so when the input signal has a low amplitude, the amplitude of the carrier wave is decreased and vice-versa. Frequency modulation: instantaneous frequency of the carrier wave is altered according to the amplitude of the input signal.
What are standing waves?
A vibration of a system in which some particular points remain fixed while others between them vibrate with the maximum amplitude.
Name 2 reasons standing waves may occur.
Medium is moving in the opposite direction to the wave, Stationary medium as a result of interference between two waves traveling in opposite directions.
What makes a violin sound different from the piano?
Timbre. ˈtambər For example, if you hear your mother talking in another room you’re able to tell that it’s her because of her voice’s timbre. Even if your mom and sister both say the same words at the same pitch and volume, you should be able to tell who is who.
What does timbre consist of?
Timbre has been called "...waste-basket category for everything that cannot be labeled pitch or loudness." Range between tonal and noiselike character Spectral envelope Time envelope in terms of rise, duration, and decay (ADSR, which stands for "attack, decay, sustain, release") Changes both of spectral envelope (formant-glide) and fundamental frequency (micro-intonation) Prefix, or onset of a sound, quite dissimilar to the ensuing lasting vibration
Waveform is a graph of a signal with amplitude (y-axis) and time (x-axis). Name 2 common shapes of a waveform!
sine sawtooth square triangle
Dependent vs Independent variable in the experiment?
Independent variable: is the one the experimenter controls. Dependent variable: is the variable that changes in response to the independent variable. The independent and dependent variables may be viewed in terms of cause and effect. If the independent variable is changed, then an effect is seen in the dependent variable.
Give an example of a dependent and independent variables in the experiment.
For example, a scientist wants to see if the brightness of light has any effect on a moth being attracted to the light. The brightness of the light is controlled by the scientist is independent variable. How the moth reacts to the different light levels is dependent variable.
What axes should dependent and independent variables be drawn on?
Independent variable: x-axis Dependent variable: y-axis
What is a fundamental frequency of a wave form?
Fundamental frequency if the lowest frequency of a periodic waveform. All of the other waveforms correspond to the harmonics or overtones of the sound. Fundamental frequency is always the loudest (see the image).As you can see by the image below, the waveform in yellow is known as the fundamental frequency while the waveforms in white are the harmonics/overtones.
What's considered to be a pitch of the note?
This note's fundamental frequency! Since the fundamental is the lowest frequency and is also perceived as the loudest, the ear identifies it as the specific pitch of the musical tone. The individual partials are not heard separately but are blended together by the ear into a single tone.
How many harmonics (apart from the fundamental frequency) does a sound have to possess in order for it to be identifiable?
7 additional harmonics! Otherwise it may be hard to identify for a human where a sound comes from. It's estimated that a sound must contain the fundamental plus as many as 7 additional harmonics in order for it to be identifiable and possess dense timbre.Therefore, if a sound possesses less than 7 harmonics, it may be harder for the human ear to identify what the sound source actually is.
Why does the same musical note played on different instruments sound different?
Because of the additional harmonics! Presence of higher harmonics in addition to the fundamental causes variation in the timbre, which is the reason why the same musical note (the same frequency) played on different instruments sounds different.
Partials VS overtones VS harmonics???
Fundamental frequency + All other frequencies = partials. All other frequencies = overtones. Fundamental frequency + All other frequencies that are perfect integer multiples of the fundamental = harmonics. All of the frequency components that make up the total waveform, including the fundamental and the overtones, are called partials. Together they form the harmonic series. Overtones which are perfect integer multiples of the fundamental are called harmonics. The fundamental frequency is consid…
What are overtones?
All frequencies higher than the fundamental frequency of a sound.
What is modulation? (in context of data transmission)
Modulation is the process of mounting original signal to the carrier wave. Unlike a radio signal (which usually has a very low frequency), a carrier signal has a constant amplitude and frequency, i.e. a constant waveform, which helps to carry the radio signal over long distances. The process of ‘mounting’ the original signal to a carrier wave is called modulation.
Sound is a longitudinal wave - an alternating pressure in the air. How is sound converted into the sine wave on a graph?
It's a graph of time VS pressure. (a) Plot of sine-wave pressure changes for a pure tone.(b) Pressure changes are indicated by darkening (pressure increased relative to atmospheric pressure) and lightening (pressure decreased relative to atmospheric pressure).
Can these travel through vacuum: sound light
sound - no light - yes
When you hear a police siren, in which direction do the air molecules between you and the siren move?
Vibrate towards you and away from you.
Sound is just an alternate compression of air pressure. Name approximate atmospheric pressure VS pressure difference that is just audible?
atmospheric pressure: 105Pa audible pressure difference: 2*10-5Pa Pa = N/m2 Atmospheric pressure (caused by the weight of the atmosphere on the ground) is approximately 100kPa (105Pa), while the amplitude of pressure differences corresponding to a wave that is just audible is about 20µPa (2×10−5Pa).
In air, pressure waves propagate at about 340ms−1 , independent of their amplitude (the maximum displacement from the rest position), wavelength (distance between successive compression maxima) or frequency (time between repeats).
However, the speed of sound waves through other media is different: in water, for example, the propagation speed is about 1500ms−1 .
What does SPL stand for?
Sound Pressure Level Sound pressure level (SPL) or acoustic pressure level is a logarithmic measure of the effective pressure of a sound relative to a reference value.
Here is a formula for SPL. What is usually taken as Pref?
Pref is the pressure of the smallest sound we can hear, 2.0×10-5 Pa. The commonly used reference sound pressure in air iswhich is often considered as the threshold of human hearing (roughly the sound of a mosquito flying 3 m away).
What is [3] and [4] on this picture?
silence audible sound atmospheric pressure sound pressure
How many decibels is 20 micropascal?
Adding the notation SPL, for sound pressure level, indicates that we have used the standard pressure of 20 micropascals as po in our calculation. In referring to the decibels or sound pressure of a sound stimulus, the term level or sound level is usually used.
Waveforms VS frequency spectra?
The position of each line on the horizontal axis indicates the harmonic’s frequency, and the height of the line indicates the harmonic’s amplitude. Frequency spectra provide a way of indicating a complex tone’s fundamental frequency and harmonics without drawing the tone’s waveform.
What makes the same letters (C, C) on the piano sound the same (when do the notes have the same tone chroma)? As we move from the low to the high end of the piano keyboard, something else happens: the letters of the notes A, B, C, D, E, F, and G repeat, and we notice that notes with the same letter sound similar. Because of this similarity, we say that notes with the same letter have the same tone chroma.
Notes with the same chroma have fundamental frequencies that are multiples of one another. Thus, fundamental frequency of: A1 - 27.5 Hz, A2 - 55 Hz A3 - 110 Hz. Somehow this doubling of frequency for each octave results in similar perceptual experiences. Thus, a male with a low-pitched voice and a female with a high-pitched voice can be regarded as singing “in unison,” even when their voices are separated by an octave or more.
What happens if we remove the fundamental frequency (200Hz)?
Tone's pitch remains the same (even though the timbre changes!). The pitch, therefore, is determined not by the presence of the fundamental frequency, but by information, such as the spacing of the harmonics and the repetition rate of the waveform. Tremendous demos: http://auditoryneuroscience.com/pitch/missing-fundamentals
Male voice is 100Hz (85 to 180 Hz). Telephone can only reproduce frequencies above 300Hz (300 to 3400Hz). How do we hear male voice as low?
When enough harmonic series are present, there will appear the phantom fundamental tone. The phenomenon of periodicity pitch has a number of practical consequences. Consider, for example, what happens when you listen to someone talking to you on the telephone. Even though the telephone does not reproduce frequencies below about 300 Hz, we hear the low pitch of a male voice, which contains frequencies below 300 Hz, because of periodicity pitch created by higher harmonics.
What 2 things do we need to know to determine loudness of the sound?
SPL (amplitude) Frequency Another way to understand the relationship between loudness and frequency is by looking at the equal loudness curves in Figure 11.9. These curves indicate the number of decibels that create the same perception of loudness at different frequencies.
What's place theory of hearing?
According to place theory, low frequencies cause maximum activity in the hair cells and auditory nerve fibers at the apex end of the basilar membrane high frequencies cause maximum activity in hair cells and auditory nerve fibers at the base of the basilar membrane. Békésy proposed the place theory of hearing, which states that the frequency of a sound is indicated by the place along the cochlea at which nerve firing is highest. There are hair cells associated with each place along the basilar…
What does this motion of the basilar membrane indicate? Basilar membrane
This is a travelling wave for some particular frequency. Each wave frequency has a different envelope, which peaks at point P. Vibration of the basilar membrane, showing the position of the membrane at three instants in time, indicated by the blue, green, and red lines, and the envelope of the vibration, indicated by the black dashed line. P indicates the peak of the basilar membrane vibration. The position of this peak on the basilar membrane is a function of the frequency of the sound. Low fr…
What's tone masking?
Auditory masking occurs in everyday experience any time your ability to hear a sound is decreased by the presence of other sounds. For example, if you are standing on the street having a conversation with a friend and the sound of a passing bus makes it difficult to hear what your friend is saying, the sound of the bus has masked the sound of your friend’s voice.
Why does the tone masking interfere more with the higher frequency than with the lower frequency?
We can see how a 400-Hz masking tone would affect the 200- and 800-Hz tones by noting how their vibration patterns overlap. Notice that the pattern for the 400-Hz tone, which is shaded, almost totally overlaps the pattern for the higher-frequency 800-Hz tone, but does not overlap the peak vibration of the lower-frequency 200-Hz tone. We would therefore expect the masking tone to interfere more with the 800-Hz tone than with the 200-Hz tone, and this greater interference is what causes the great…
In the organ of Corti - what inner hair cells VS outer hair cells are responsible for?
inner hair cells - [afferent nerve fibers], give rise to the perception of sound outer hair cells - [efferent nerve fibers], help sharpen the frequency resolving power of the cochlea
What's conductive hearing loss VS sensorineural hearing loss?
Conductive hearing loss - [outer ear] caused by physical damage to the ear (such as to the eardrums or ossicles) that reduces the ability of the ear to transfer vibrations from the outer ear to the inner ear. Sensorineural hearing loss - [inner ear] caused by damage to the cilia or to the auditory nerve, is less common overall but frequently occurs with age. While conductive hearing loss can often be improved through hearing aids that amplify the sound, they are of little help to sensorineural…
Name 2 theories of hearing. Although loudness is directly determined by the number of hair cells that are vibrating, two different mechanisms are used to detect pitch.
Place coding - we determine the frequency by the envelope of the basilar membrane. Temporal coding - we determine the frequency by neurons firing at a rate that mimics the frequency of the sound. For example, a tone measuring 600 hertz will be transduced into 600 nerve impulses a second.
At what frequencies do temporal coding VS place coding work?
Temporal coding: [20 Hz - 5,000 Hz] Place coding: [1,000 Hz - 20,000 Hz] Today, it is widely believed that hearing follows the rules of the frequency theory, including volley theory, at frequencies below 1000 Hz and place theory at frequencies above 5000 Hz. For sounds with frequencies between 1000 and 5000 Hz, both theories come into play so the brain can utilize the basilar membrane location and the rate of the impulse.
How is the frequency theory possible, if: humans can hear frequencies up to 20,000 Hz neurons fire at maximum of 500 Hz Frequency theory: 600 Hz tone will be transduced into 600 nerve impulses a second.
This is solved by the volley principle: If you have a group of neurons, each of which fire at the particular amplitude, - it's possible to measure the frequency. Volley theory suggests that groups of auditory neurons use phase-locking to represent subharmonic frequencies of one harmonic sound.
What's an octave?
Interval between one musical pitch and another with double its frequency. For example, if one note has a frequency of 440 Hz, the note one octave above is at 880 Hz, and the note one octave below is at 220 Hz. Два звука, отстоящие на октаву, воспринимаются очень похожими друг на друга, хотя явно различаются по высоте.
Harmonic VS octave?
Harmonics - f, f + f, f + f + f, ... arithmetic sequenceWhen you go up an octave - f, 2f, 4f, 8f, 16f, ... geometric sequence
If a fundamental frequency is 20Hz, what would be the 5th octave?
20Hz * 2 * 2 * 2 * 2 * 2 = 20Hz * 25 = 640Hz
What is chroma?
There are twelve chroma values represented by the set {C, C♯, D, D♯, E , F, F♯, G, G♯, A, A♯, B} Enumerating the chroma values, one can identify the set of chroma values with the set of integers {1,2,...,12}, where 1 refers to chroma C, 2 to C♯, and so on. (a) Musical score of a C-major scale. (b) Chromagram obtained from the score. (c) Audio recording of the C-major scale played on a piano. (d) Chromagram obtained from the audio recording. Chromagram looks like chords!
What's chromagram?
A graph that maps time to one if the 12 chroma values (regardless of octave). (a) Musical score of a C-major scale. (b) Chromagram obtained from the score. (c) Audio recording of the C-major scale played on a piano. (d) Chromagram obtained from the audio recording. Project all the energy of the spectrum onto 12 bins that correspond to the 12 pitch classes of the equal-tempered scale, regardless of octave. Given a music representation (e.g. a musical score or an audio recording), the main idea o…
Name 2 uses of chromagrams.
Content-based audio retrieval such as cover song identification, audio matching or audio hashing . Music alignment Identifying pitches that differ by an octave, chroma features show a high degree of robustness to variations in timbre and closely correlate to the musical aspect of harmony. This is the reason why chroma features are a well-established tool for processing and analyzing music data.
What's rhythm?
One example might be that rhythm is a complex perceptual phenomenon involving the perceptual grouping of sequences of stronger and weaker pulses. Even when the stimulus is a series of equally-spaced pulses (an isochronous pulse train, with interval less than about 1s), listeners will spontaneously group them, with groups of two, three or four pulses being overwhelmingly more common than any other grouping. Varying the pulses’ pitches, lengths, spacing or amplitudes can encourage one or other gr…
What are blue areas?
Measures.
Describe the difference in sound of left & right waveform.
i. lower pitch ii. louder iii. same
Each row below shows Fast Fourier Transforms for two examples sounds. Describe the difference between the left and the right sounds.
H is louder than G J is one octave lower than I For K and L, the timbre will be different.
A saxophonist plays a note whose pitch is perceived to be the same as a 160Hz sine wave. List 3 frequencies that are likely to be present in the saxophone sound.
Frequencies that are integer multiples of 160 Hz would be present: 160Hz * 2 160Hz * 3 160Hz * 4 Because the air column vibrates with these harmonically related frequencies.
What determines sounds of various musical instruments?
The relative amplitudes of the various harmonics primarily determine the timbre of different instruments and sounds, though onset transients, formants, noises, and inharmonicities also play a role. For example, the clarinet and saxophone have similar mouthpieces and reeds, and both produce sound through resonance of air inside a chamber whose mouthpiece end is considered closed. Because the clarinet's resonator is cylindrical, the even-numbered harmonics are less present. The saxophone's resona…
Put the bars according to the time signature
Each bar needs to be exactly 3 beats long.
What does time signature show?
How do these produce sound: saxophone violin?
saxophone - air enclosed in a tube vibrates, - persons covers the hole, and it changes the length of the pipe. violin - strings produce standing waves, - each note uses a string of a particular length. Vibrating air columns also have resonances at harmonics, like strings. #todo, important question, learn it better with physics when you get the time The natural vibrations of the air in the saxophone, the ones that cause it to play notes, are due to standing waves. Frequencies that are integer mu…
What's consonance VS dissonance?
Half objective/half subjective unpleasantness of the sound. Consonant sound: Dissonant sound: Within the Western tradition, consonance is associated with sweetness, pleasantness, and acceptability;dissonance is associated with harshness, unpleasantness, or unacceptability. Western musical styles use a large variety of chords and vertical sonorities. Based on objective acoustical properties, chords can be situated on a dissonant-consonant continuum. While this might to some extent converge with…
Name 2 causes of dissonance.
beating - the wah-wah-wah sound produced by two notes played simultaneously but with slightly different frequencies no simple ratio between two notes In most Western music dissonances are held to resolve onto following consonances, and the principle of resolution is tacitly considered integral to consonance and dissonance".
What's beating (a type of a sound)?
Wah-wah-wah sound produced by two notes played simultaneously but with slightly different frequencies. Beating is one of the causes of dissonance. Tuning two tones to a unison will present a peculiar effect: when the two tones are close in pitch but not identical, the difference in frequency generates the beating. Examples: https://en.wikipedia.org/wiki/Beat_(acoustics)#Sample.
This is the 1st, 2nd, and 3rd harmonic of some rope. What is meant by this physically?
Someone holds one end of the rope, and someone just shakes it. At some points there is little to none movement, - but at harmonics, nodes appear. https://www.youtube.com/watch?v=f4M-6tWtkoA
What harmonic is this rope in?
3rd harmonic, - because it has 2 nodes.
What does the resonance frequency in strings depend on?
T - tension L - length of the string m - mass of the string
How do you tune VS play the violin?
Violin has 4 strings, - they all 4 have a different mass tension, but about the same length. You tune the violin by changing the tension. You play violin by changing the length (you move your finger).