Week 1: Nature of Sound Flashcards
What is propagation of sound?
Sounds moving through a medium.
T/F
Sound moves through different mediums at different speeds?
True
How do we determine if a sound is coming from one side or the other? Why does this matter for sound production?
If the sound is coming from the right it hits your right ear first and your brain can determine the direction from the delay.
Manipulation of this slight delay, manipulation of propagation gives the effect of this direction.
What properties of air can change the rate of sound?
- Temperature
- Humidity
- Elevation
What is the approximate speed of sound?
340 m/s
1 ft/ms
1km/3s
1mi/5s
What types of sound effects are related to propagation?
Delay, reverb, phasers, flangers.
What determines our sense of space and depth for sound?
Propagation and reflection.
Sound reflecting off objects and the different amount of time it takes to get to your ears from different surfaces.
What is Amplitude?
Amplitude is the extent of the wave - how wide it is moving, how much the air compresses and rarefies as the wave form moves or propagates.
What is the difference between a wave on a pond and in the air?
A wave on a pond is a flat surface with vibrations of top of it - the vibration is perpendicular, at a right angle to the direction of propagation.
Sound waves in air are parallel - in the same direction of propagation.
(Spring demonstration of waving side to side - transverse wave, vs the push/compression longitudinal wave)
The amount of compression in a sound wave is the …
amplitude.
The amplitude in a transverse wave in a spring is…
the amount it is waved back and forth (looks like width in the video).
Sound is what type of wave?
Longitudinal
What is compression?
The air getting more dense by the way it moves.
What is rarefaction?
The air getting less dense by the way it moves.
How do we perceive compression and rarefaction?
Loudness.
The higher the amplitude (more compression) the louder.
Amplitude is measure in what units?
Decibels
What is dBSPL?
Decibels of Sound Pressure Level - a measure of amplitude in the air.
Decibels are a relative or absolute measure?
Relative
There is no definite set point where zero is.
dBSPL is related to…
the threshold of hearing - the quietest thing we can possibly hear in the air.
In the digital domain amplitude is measured with ____ and related to ____.
DBFS (Decibels of Full Scale) aka Full Scale
related to the loudest thing that could be represented by numbers within the computer.
How do the numbers work with digital amplitude measurement?
Zero is the loudest thing that can be represented by the computer and it goes negative from there.
How do the amplitude numbers related in digital vs air measurements?
You’ll see negative DB in the computer and positive DB in the air.
What is the difference between amplitude and loudness?
Amplitude is something measurable (e.g. by the computer) and loudness is our perception of that. Our perception of amplitude is complex and includes many other factors including duration and frequency.
What is panning?
Controlling the level between two speakers.
What is the dynamic range of a microphone?
The decibels in which it will reproduce the sound properly.
When you are talking about the dynamic range of a piece of gear it ranges between…
noise floor and distortion
- the noise floor or the quietest sound that can be produced clearly above the the hiss that the device is putting out
- distortion when the sound is so loud it can’t reproduce it and gives an ugly crackling or upper harmonics to the signal.
What is dynamic range of a piece of music?
The range from its quietest to loudest section.
Video Quiz T/F
The threshold of hearing is 0 dBSPL.
True
This is the quietest thing that can be heard.
Video Quiz T/F
The maximum amplitude inside the computer is 0 dBSPL.
False.
The maximum amplitude inside the computer is not 0 dBSPL. It is 0dBFS or 0 decibels Full Scale.
“When producing music, ____ becomes a primary concern. Our functions of mixing is largely based on controlling the ____ of our many tracks and making them relative to each other in a pleasing way…”
amplitude
4 examples of dynamic plugins are…
expanders, gates, compressors, and limiters
What are
Equal-loudness contours
This term refers to a contour that represents a constant loudness for all audible frequencies. A contour having a sound pressure level (SPL) of 40dB at 1kHz is arbitrarily defined as a 40-phon contour.
-Sweetwater
What are
Fletcher–Munson curves
Fletcher and Munson were researchers in the ’30s who first accurately measured and published a set of curves showing the human ear’s sensitivity to loudness verses frequency. They conclusively demonstrated that human hearing is extremely dependent upon loudness. The curves show the ear to be most sensitive to sounds in the 3kHz to 4kHz area. This means sounds above and below 3–4kHz must be louder in order to be heard just as loud. For this reason, the Fletcher-Munson curves are referred to as “equal loudness contours.” They represent a family of curves from “just heard,” (0dB SPL) all the way to “harmfully loud” (130dB SPL), usually plotted in 10dB loudness increments. Though the Fletcher-Munson Curves are by far the most widely known contours, there have been others defined in recent years that some engineers think are more accurate
- Sweetwater
What is a
phon
A subjective unit of apparent loudness. A phon is defined as the sound pressure level of a pure sine wave tone that sounds equal in loudness to some other sound(s) in question. Because of the ear’s complicated response versus frequency characteristics (see Fletcher Munson Curves) you can’t accurately relate the perceived loudness of sounds directly to their sound pressure level as read on a sound level meter. The phon allows us to relate this perceived loudness of sound to objective measurements of that loudness.
-Sweetwater
How do we perceive frequency?
We perceive frequency as high and low pitch and we tend to use “frequency” and “pitch” interchangeably.
Frequency is related to how fast sound is vibrating. A low frequency wave has slow pulses and a high frequency wave has fast pulses.
What is the dependence between frequency and amplitude?
They are independent. You can have a high frequency, low amplitude wave/sound or a low frequency, high amplitude wave/sound.
This is important because audio effects can be utilized that impact only certain parts of the sound.
What is timbre?
Timbre is the collection of sound in multiple frequencies.
This might also be referred to as the spectrum.
What kind of wave is the simplest sound?
A single frequency sine wave.
But that rarely happens. Every instrument has energy at multiple frequencies.
What is sound at multiple frequencies from an instrument called?
Harmonics, also called overtones or partials.
What does it mean to boost the bottom end on a equalizer in terms of sound properties?
Raise the amplitude of the bottom frequency.
What is the relationship between an equalizer and filters?
An equalizer is a collection of filters (e.g. a filter that changes the amplitude of different frequencies.).
What is the approximate lowest and highest frequency in human hearing?
Lowest - 20 Hz
Highest - 20,000Hz=20kilohertz (young children can hear this but your high end dissipates naturally as you get older)
Adults hear about 18,000Hz (18 kilohertz) at the upper end. with females hearing slightly higher.
What is 1 Hertz?
1 vibration per second.
How does hearing change across the frequencies?
As we get to the higher or lower ends it gradually diminishes and there are variations in the middle.
It’s as if our ears act like an EQ and equipment has this kind of frequency response curve as well.
Frequency Response
Frequency Response is the Frequency Range versus Amplitude. In other words, at 20 Hz, a certain input signal level may produce 100 dB of output. At 1 kHz, that same input level may produce 102 dB of output. At 10 kHz, 95 dB, and so on. A graph of all the frequencies plotted versus level is the Frequency Response Curve (FRC) of the monitor.
When you see a Frequency Response specification for a monitor, the manufacturer is telling you that for a given input signal, the listed range of frequencies will produce output within a certain range of levels. For example: 20 Hz to 20 kHz +/- 3 dB. For these frequencies, the monitor will output signals that are within a 6 dB (+/- 3 dB) range. This does not mean that the speaker won’t reproduce frequencies outside this range, it will! But frequencies outside the range will be more than 3 dB off from the reference level.
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Psycho acoustics
The way we perceive sound.
A field of science that studies how we perceive sound and extract useful information from acoustical signals. It concerns itself primarily with low-level functions of the auditory system and thus doesn’t much overlap with the study of music or aesthetics. Basic psychoacoustical research is mainly directed toward such topics as directional hearing, pitch, timbre and loudness perception, auditory scene analysis (the separation of sound sources and acoustical influences from sound signals) and related lower functions, such as the workings of our ears, neural coding of auditory signals, the mechanisms of interaction between multiple simultaneously heard sound sources, neural pathways from ears to the auditory cortex, their development and the role of evolution in the development of hearing. Psychoacoustical research has resulted in an enormous amount of data which can readily be applied to sound compression, representation, production and processing, musicology, speech recognition and composition, to give just a few examples.
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Masking
When any sounds that contain similar frequencies are played simultaneously, the weaker sound tends to have those overlapping frequencies covered – ‘masked’ – by the frequencies from the stronger sound (especially in a dense mix). The frequencies of the weaker sound are still there; they are just not discernable over the more dominant sound with the same frequencies. Masking is a fact of life in audio, and not entirely a bad thing, either. Often when sounds are masked you tend to not miss them. An example of practical applications where masking plays a big part are audio CODECs, which often identify and eliminate masked sounds from an audio file in order to make the overall file size smaller.
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Fundamental
In audio the fundamental is the frequency of the root, or core pitch making up a pitched sound. Except for a few special cases the fundamental is always the lowest frequency making up any pitched sound and is generally the strongest pitch we hear (in a strict Physics sense the fundamental is, by definition, the lowest pitch of a sound). Most sounds are comprised of a combination of a fundamental pitch and various multiples of it known as overtones. When overtones are added to the fundamental, which occurs in almost all naturally occurring sounds, the character of the sound is changed. The relationship between the fundamental and the overtones are what gives each sound its basic timbre.
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Timbre
Pronounced “tamber,” it is the subjective quality or tone color of a sound; the essential quality of a sound that makes it what it is. An oboe has a different timbre than a tuba, for example. Two oboes may have a slightly different timbre from one another. They sound different. Timbre is made up of all of the qualities of a sound: transient attack, harmonic content, envelope, overtone structure, and more.
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Envelope
The envelope of a sound can be explained as a variation that occurs to it over time. How a sound starts, continues, and disappears in terms of pitch, harmonic content, and loudness is a function of its envelope. An envelope generator is a circuit or algorithm found in most synthesizers that provide a means to apply these kinds of changes to a sound over time.
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Phantom fundamental
A harmonic sound is said to have a missing fundamental, suppressed fundamental, or phantom fundamental when its overtones suggest a fundamental frequency but the sound lacks a component at the fundamental frequency itself. The brain perceives the pitch of a tone not only by its fundamental frequency, but also by the periodicity implied by the relationship between the higher harmonics; we may perceive the same pitch (perhaps with a different timbre) even if the fundamental frequency is missing from a tone.
For example, when a note (that is not a pure tone) has a pitch of 100 Hz, it will consist of frequency components that are integer multiples of that value (e.g. 100, 200, 300, 400, 500…. Hz). However, smaller loudspeakers may not produce low frequencies, and so in our example, the 100 Hz component may be missing. Nevertheless, a pitch corresponding to the fundamental may still be heard.
-wikipedia
Video Quiz T/F
True or False: The more pulses in a sound wave, the higher the frequency and the lower the pitch.
False.
The more pulses in a sound wave, the higher the frequency and the higher the pitch.
If propagation and frequency were related such that high frequency sounds had faster propagation what would happen to chords?
We’d hear chords one note at a time with the higher pitches arriving first.
(So it’s good that amplitude/propagation and frequency are independent).
What is a compressor?
A compressor is a device that reduces the dynamic range of an audio signal.
There are a variety of uses and applications for compressors, the most obvious one being to control the dynamic range of a live performance so that it will fit into the fairly narrow dynamic range of recorders, etc. Other applications include making a signal’s average level higher, increasing the apparent sustain on a guitar, evening out a vocal or bass guitar performance, fattening up sounds, and on and on. The list of possibilities is extensive!
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What is a gate?
A dynamics device whose function is to remove unwanted audio material below a certain threshold. Some type of “gain cell” is employed (usually a VCA) that can raise or lower the volume of the audio going through the unit. When the signal falls below a certain threshold that is set the gain cell will quickly drop the audio level down to a predetermined level. This level is usually very low, or even off, but in some applications it may only be a reduction of a few dB. The reason they are called gates is because when they “close” it sounds as if the audio has suddenly stopped, or has been “gated.” Now, it is possible to set many gates for slower response time so the effect is not as sudden, but often a sudden change is what is desired. Gates are often used on drum tracks to prevent bleed from other nearby drum mics, and they are sometimes used on noisy sources so when the desired audio signal stops the noise is automatically muted. The gated reverb sounds made popular by Phil Collins and Peter Gabriel in the 1980’s were the result of running a reverb’s decay through a gate. When the reverb level fell below a certain threshold the sound would abruptly cut off.
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What is an expander?
The opposite of a compressor. Where a compressor takes a given dynamic change and reduces it, an expander increases it, making changes larger. Expanders are used to “un-do” compression in some circuits (companding). More commonly, expanders are used for noise reduction. In this application (downward expansion), a threshold is set at a level below desired audio signals, but above the noise floor. When signal drops below the threshold, expansion is applied, pushing signal even further down, reducing the level of noise. For example, an expander might be set up with a 1:6 ratio. This means that for every 1 dB of input level change the expander sees, it will output a 6 dB change. When a signal drops below the threshold by 2 dB, the output of the expander will drop by 12 dB, similarly dropping the level of any background noise floor.
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What is a limiter?
A limiter is a dynamics processor very similar to a compressor (see inSync WFTD 10/13). In fact, many compressors are capable of acting as limiters when set up properly. The primary difference is the ratio used in reducing gain. In a limiter, this ratio is set up to be as close to infinity:1 as possible (no matter how much the input signal changes, the output level should remain pretty much constant). The idea is that a limiter establishes a maximum gain setting, and prevents signals from getting any louder than that setting.
Like compressors, limiters are used for a variety of applications. A few: Maximizing signal levels while preventing distortion when using digital recorders, preventing overload in a signal chain, setting a maximum volume level to protect users of in-ear monitors, protecting speakers and amplifiers from clipping, and so on. Any time you want to establish a maximum gain setting and prevent signals from passing it, a limiter is your tool of choice!
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What is the first thing a compressor does?
First a threshold is established. When the audio signal is louder than this threshold, its gain is reduced. The amount of gain reduction applied depends on the compression ratio setting. For example, with a 2:1 ratio, for every 2 decibels the input signal increases, the output is allowed to increase only 1 decibel. A variety of other parameters in the compressor will also affect its performance processing specific signals; attack time, release time and others are very important.
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What is threshold?
A parameter found on compressors, limiters and noise gates (and a variety of other dynamics-based processors), the threshold setting determines at what level the processor will begin working. For example, on a compressor, when signal level exceeds the threshold setting, it will be compressed; below the threshold signal will be passed unprocessed. On a gate, threshold determines the minimum input level required to cause the gate to open up and pass signal; when input level drops below the threshold, the gate will be closed preventing signal from passing. Carefully setting the threshold allows you to very specifically control when processing is being applied to a signal.
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What is Ratio?
In a compressor, limiter, or expander, ratio is the amount of output level change that results from a given input level change. For example, in a compressor with a 4:1 ratio, an input level increase of 4 dB will result in an output increase of only 1 dB. An expander might have a ratio of 1:4; for a 1 dB input change, a 4 dB output change will result. Limiters typically have extremely high ratios, some claiming infinity:1, which essentially means that for virtually any input level increase, there will be only a very minor output level increase.
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Video Quiz:
Which of the following are part of the timbre for any given instrument? Multiple may apply.
Frequencies
Partials
Sine Waves
All three.
Timbre is comprised of a multitude of frequencies.
Partials are part of the timbre for a given instrument.
Sine waves represent a single frequency. Since timbre is comprised of a multitude of frequencies, this means that timbre is also comprised of a multitude of sine waves.
Video Quiz:
If you were asked to soften the top end you would…
Decrease the amplitude of the high frequencies.
Why is sound hard to visualize?
Because it’s a longitudinal (not transverse) wave.
What three different display types give us a good visual of sound?
- Oscilloscope display
- Spectrum analyzer
- Spectrogram analyzer
What three different display types give us a good visual of sound?
- Oscilloscope display
- Spectrum analyzer
- Spectrogram/Sonogram analyzer
What is the spectrum analyzer display and its drawback?
On the spectrum analyzer display the horizontal shows the frequency and the vertical shows the amplitude. So we can see that this sound has a lot of energy at 2k or 1k or 500Hz and associating those numbers to the sound we hear.
The problem is it is momentary and doesn’t show us how things change over time.
What is the spectrogram analyzer?
The spectrogram analyzer is like the spectrum analyzer but repeated over time. So we get a sense of how the timbre, frequency and amplitude all change over time and most closely represents the way we hear.
Video Quiz?
Which display shows time on the horizontal (X) and amplitude on the vertical (Y)?
Oscilloscope view
Video quiz:
Which display is like a typical waveform shown in a DAW track?
Oscilloscope
What does an Oscilloscope display show in terms of the physics?
Exactly how the pressure is varying in the air or the voltage is varying in a wire.
If you change the amplitude of a sound in the Oscilloscope display, what happens?
The height of the waveform increases.
If you play a higher note in the Oscilloscope display, what happens?
The number of repetitions (per second, assuming the zoom doesn’t change) increases.
For example going from one C to the next octave C doubles the frequency (repetitions over time).
What has changed if you go from a sine wave to a sawtooth wave?
Timbre
A peak on a spectrum analyzer represents___
and ___ is on the vertical scale.
the frequency of the pitch
amplitude
What does a sawtooth wave look like on the spectrum analyzer? What is this called?
A series of peaks, the largest at the fundamental and the others at multiples of the fundamental.
The is called the harmonic series (which is a major function of timbre).
You will often see spectrum analyzers in (x) because the function of (x) is to manipulate the (y).
x= EQs
y=timbre
The sonogram analysis is like the spectrum analysis ___.
flipped on its side - instead of having frequency left to right frequency is up and down and time is going by slowly horizontally.
In the demonstration, what changes in the Sonogram display as the amplitude changes?
It changed color (from blue to green).
Video Quiz
Which of the three displays shows X-Time Y-Frequency Z-Amplitude?
The Spectrogram/Sonogram shows X-Time Y-Frequency Z-Amplitude.
In the demonstration of singing vowels on a single pitch, what changed in the Spectrogram and how does that relate to the “instrument” of the voice?
The harmonics changed depending on which vowel he was singing (for instance there was a gap around 1 khz when he was signing A and E but it was filled in for I and the pitch/harmonics changed while singing U because it has multiple sounds.
The mouth is emphasizing and removing certain parts of the frequency range that is created by the vocal folds.
The vocal folds would be like an oscillator/sound generator and the mouth is like a filter/EQ.
Video Quiz
True or False: Vowel sounds are primarily variations of amplitude.
False
Vowel sounds are primarily variations of SPECTRUM, not amplitude.
