| Acoustical Properties of Sound |
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| The physical characteristics of what we hear (frequency, amplitude, envelope, harmonic spectrum) |
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| Perceptual Properties of Sound |
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Describing how we hear and perceive (louder, softer, duller etc). (Pitch, Loudness, Articulation, Timber)
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| Created patterns pulled and pushed apart creating an increase and decrease in energy where each vibration creates a similar cycle (periodic waveform) |
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| The measure of oscillation (the number of cycles over a period of time). When the frequency of oscillation gets higher the pitch increases and vice versa. |
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| Magnitude of the oscillation or the increase and decrease of pressure produced by a vibration. (Measured in various ways including decibels |
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| Pattern of amplitude change over time where each instrument will have a distinctive envelope (4 Parts: attack, decay, sustain, release) |
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| amplitude of each of the frequencies that make up the sound (another part of the timber plus envelope) |
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all periodic vibrations contain frequencies or overtones above the fundamental (first harmonic) using standard set of ratios.
First overtone – second harmonic
Second overtone – third harmonic
etc.
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| Sampling Rates and quantizing |
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the quality of the digitized sound depends on the accuracy of the original analog data and the quality in which the computer samples the file.
Sampling rate- the speed at which the computer converts from analog to digital.
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| Digital Sampling and Human Hearing |
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| Upper level of human hearing is 20 kHz, so we should use sampling rate of the frequency limit 44kHz which is 1/2 the sampling rate,or 22kHz |
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| 2 rules of digital sampling |
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1. The sampling rate must be 2X the upper limit of the range of human ear (2 X 20kHz =40kHz) which will give us a sampling quality equal to or better than the input
2. The usable dynamic range is a ftn of the sampling width S/N which shows that the greater the numeric the better the measurement. (So the larger S/N is the less likely errors will be detectable)
the dynamic range of a sampled sound or its signal-to-noise ratio is the sampling width (W) * 6dB
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| Sounds in output that are unwanted/add distortion. |
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The rate we use for sampling audio must be twice as high as the usable frequency we need.
- NT: The usable frequency range of sounds is 0 to one-half of the sampling rate (S/2)
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Two filters help prevent aliasing.
1. Low pass filter – before the analog-to-digital conversion
2. High pass/brickwall filter – before the digital-to-analog converter, blocks most sounds above 22kHz to pass through (they hit a “brick wall”)
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| a filter that increases the sample rate by adding more samples between the ones coming in from analog sample. (this removes the distortion out of the human range of hearing) |
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| any periodic vibration can be expressed as a series of sine waves. |
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| Lossless Vs. Lossy Compression |
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Lossless: The computer eliminates information, but when reconstructed restores the data back to its original form
Lossy: some amount of the original material is lost during compression
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combines oscillators to build up complex sounds. (By adding waves; at varying amplitudes you can create different harmonic spectrum)
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| takes a complex sound like a saw tooth wave and filters out certain harmonics to alter the series (harmonic spectrum) |
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| a physical property of sound to distort it (frequency modulation synthesis accomplished with and oscillator/modulator) |
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| simulates the acoustical properties of musical instruments using mathematical formulas |
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| slicing and dicing of sound into “small grains” and doing things with them to create various effects |
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- Normailization (the wave form is adjusted to be no louder than the highest peaks of sound that will not be distorted).
- Compressor (boost the lows and compress the highs for better balance).
- Panning (moving the signal around the channels to give the illusion of sound in space)
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| Time – Dry sound and wet sound |
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Dry sound – original audio
Wet sound – same audio fed back into signal at different time/intensity.
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| Echo effect, Chorusing, Flange, Reverb |
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- echo – create an echo effect with a certain delay time
- chorusing – offset the signal to create a fuller slightly out of tune signal sound
- flange – chorus with shorter delay. Creates a sweeping swooshing sound
- reverb – creates acoustical properties of a closed space
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- Removing noise/Adding Silence/Adding Noise
- Balance the frequencies of the audio spectrum by filtering out certain ranges of the spectrum
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| Balanced and unbalenced connectors |
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- Unbalanced – wire carries only for a signal and the other for ground. TS
- Balanced – two discrete wires provided for the singal and a third wire for ground. TSR and XLR
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resistance to the electrical current (measured in Ohms).
The lower the impedance the better. Wood quality wire is at 75 Ohms or lower
XLR connectors for pro mics, with phantom power for low impedance
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