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The shaping and manipulating of
representations of sound by an electronic
music system. |
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An instrument that produces an analog or
digital representations of sound, which the
user may design. |
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| An instrument represents sound as voltages |
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An instrument represents sound as a series of
discrete numbers |
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| Electro-acoustic Transducer |
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An electroacoustic transducer converts
electrical energy to acoustic energy
There are always relatives between the two
types of energy.
Fluctuations in voltage are analogous to
fluctuations in air pressure.
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An electrical signal that represents sound by
containing voltages that fluctuate analogously
to the fluctuations contained in the air
pressure. |
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Fluctuations in voltage are
converted to imprints on
magnetic tape, then back
into an analog signal by tape
player. |
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| Analog to Digital Converter |
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a device which changes an analog signal to a
digital representation of sound. This digital
representation is a series of numbers that
represents the fluctuating voltage of the
analog signal
Once in digital form the signal may then be
shaped and modified using digital tools. It may
also be sent to tape or disk where it is
encoded and stored as a digital recording.
This type of recording is called a digital
recording because the sound is stored as a
series of discrete numbers. |
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| Digital to Analog Converter |
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a device which takes the series of stored
numbers, the digital representation of sound,
and changes it back to an analog signal. |
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| A graphic depiction of sound
Shows fluctuation Air pressure, voltages or digital
values over time. |
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The process of converting and analog signal
to a digital representation of sound by taking
measurements of instantaneous amplitudes
at equally spaced time intervals. |
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Time-domain
representation |
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Waveform shows Amplitude changes through
time proceed.
Focused on depiction of Amplitude. |
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Frequency-Domain
Representation |
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A graph of all frequency components of
sound. |
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refers loosely to the
strength of the waveform
in terms of the amount of
fluctuation between the
peak positive value or the
peak negative value and
the zero axis |
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the rate at which one cycle of
a waveform is completed. Measured by the
number of cycles per second (Hz)
X-Axis |
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| Frequency vs. Pitch (Directly correlated) |
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| Frequency is the physical property of sound
Pitch is the listener’s interpretation of frequency |
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The term phase is used to specify a
specific point in time on a waveform
Phase can also be used to compare the
relative position in time of two waveforms |
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The rate at which measurements of
amplitude are taken
– expressed in samples per second
– like frequency, measured in Hz
The sampling rate directly affects the quality
of the conversion
– higher rates mean a better representation of the
original sound
– higher sampling rate = bigger files and more
processing power needed |
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False or alias frequencies that arise from
a sampling rate that is too slow in the
analog to digital conversion process. Also
called “ Fold over ”
Samples must be very close together in
order to create a convincing illusion of
continuous sound
Unwanted frequencies produced when a
sound is sampled at a rate less than
twice the highest frequency component in
the sound. |
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False or alias frequencies that arise from
a sampling rate that is too slow in the
analog to digital conversion process. Also
called “ Fold over ”
Samples must be very close together in
order to create a convincing illusion of
continuous sound
Unwanted frequencies produced when a
sound is sampled at a rate less than
twice the highest frequency component in
the sound. |
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A sampling rate two times the highest
frequency contained in a waveform.
• To Avoid aliasing: sample at a rate of at least
twice the highest frequency in a sound.
• At least two data points per cycle guarantees
frequency. |
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The number of discrete
amplitudes a digital system can
represent.
• Expressed in terms of the number of bits
used to store each amplitude-level
• Also called Quantization
• Detail and dynamic range |
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Fourier Analysis: named after the nineteenth
century French mathematician Jean Baptiste
Fourier, enables one to break down complex
periodic waveforms into their basic components,
which happen to be sine waves of various
frequencies, amplitudes, and phases.
Fourier Synthesis: The opposite method,
combining sine waves of various frequencies,
amplitude, and phase to create complex periodic
waveforms, is Fourier Synthesis.
Additive synthesis is a synthesis
technique that is based on the
combining of simple waveforms
(usually sine waves) at a various
frequencies, amplitude and phases to
create a more complex waveform. |
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Frequency is uniform
• Smooth, “pure” sound
• Generally regarded as the most basic
waveform, thanks to Fourier |
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the frequency component that has
the same period as the waveform |
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any frequency in a waveform higher than
the fundamental |
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a frequency that is a whole-number
multiple of the fundamental
the fundamental is the first harmonic of the
harmonic series |
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any harmonic other than the
fundamental
the first overtone is the second harmonic |
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Contains all harmonics
• amplitudes in a ratio of 1/harmonic #
• even harmonics 180 degrees out of phase
• has a buzzing sound to it |
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Contains only odd harmonics
• amplitudes in a ratio of 1/harmonic # squared
• every other harmonic is 180 degrees out of phase
• smooth sounding, like a clarinet |
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like the triangle wave, contains only odd harmonics
• like the sawtooth wave, amplitudes in a ratio of 1/
harmonic #
• all harmonics in phase |
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subtractive synthesis
a synthesis technique that is based
on the removal or attenuation of
specified frequencies by a filter |
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allows only certain frequencies to pass
• basic part of almost all synthesis systems
• Cutoff Frequency: the specific frequency
above which, or below which, (depending
on the filter type) frequencies are removed
or attenuated. |
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Attenuates frequencies above the CUTOFF
FREQUENCY while allowing frequencies
below the cutoff to pass unaltered
– The difference between the input and the
output is called the FREQUENCY
RESPONSE |
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| Attenuates frequencies below the cutoff |
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allows a specific band of frequencies to
pass while attenuating others |
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opposite of band-pass; attenuates a
specific band of frequencies while letting
others pass |
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when regeneration is increased, the
frequencies around the cutoff increase are
given more prominence |
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a graphic depiction of how a filter, synthesis
module, or other electronic device responds to
a signal. |
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The difference between the input and the
output is called the FREQUENCY
RESPONSE |
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