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In physics and engineering, the envelope of an oscillating signal is a smooth curve outlining its extremes. [1] The envelope thus generalizes the concept of a constant amplitude into an instantaneous amplitude. The figure illustrates a modulated sine wave varying between an upper envelope and a lower envelope. The envelope function may be a ...
In sound and music, an envelope describes how a sound changes over time. For example, a piano key, when struck and held, creates a near-immediate initial sound which gradually decreases in volume to zero. An envelope may relate to elements such as amplitude (volume), frequency (with the use of filters) or pitch.
Diagram of beat frequency. In acoustics, a beat is an interference pattern between two sounds of slightly different frequencies, perceived as a periodic variation in volume whose rate is the difference of the two frequencies. With tuning instruments that can produce sustained tones, beats can be readily recognized.
For each centre frequency, the signal can be considered as a slowly-varying envelope (E BM) imposed on a more rapid temporal fine structure (TFS BM). The envelope for each band signal is shown by the thick line. Notions of temporal envelope and temporal fine structure may have different meanings in many studies.
Formant frequencies, in their acoustic definition, can be estimated from the frequency spectrum of the sound, using a spectrogram (in the figure) or a spectrum analyzer. However, to estimate the acoustic resonances of the vocal tract (i.e. the speech definition of formants) from a speech recording, one can use linear predictive coding.
Sometimes the phrase "complex envelope" is given the simpler meaning of the complex amplitude of a (constant-frequency) phasor; [a] [b] other times the complex envelope () as defined above is interpreted as a time-dependent generalization of the complex amplitude.
Undertone series on C. [1] In music, the undertone series or subharmonic series is a sequence of notes that results from inverting the intervals of the overtone series.While overtones naturally occur with the physical production of music on instruments, undertones must be produced in unusual ways.
[3] [4] The inverse of the wavelength is called the spatial frequency. Wavelength is commonly designated by the Greek letter lambda (λ). For a modulated wave, wavelength may refer to the carrier wavelength of the signal. The term wavelength may also apply to the repeating envelope of modulated waves or waves formed by interference of several ...