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Entries found for search: phase

antiphase : See out-of-phase, phase reversal.

bi-phase : An electronic reference signal used by mag recorders, editing stations, and film projectors. See bi-phase modulation, pilot tone, neo-pilot, and control track.

bi-phase modulation : In SMPTE timecode generation, the electronic process that produces the signal containing the SMPTE data itself. A 1.2k Hz square wave is momentarily modulated to 2.4kHz with each new bit of location information coming from the master clock.

bi-phase/tach : An electronic pulse used by some film equipment and other motor-driven devices. Similar to a bi-phase signal, but different in the way directional information is provided. See also tach pulse.

phase distortion : An effect caused when phase-shift in an audio device is not a linear function of frequency. In other words, different frequencies experience different time delays. This changes the waveform of the signal and is especially injurious to transients. Most transducers produce significant phase distortion. As low frequencies travel slightly faster than high frequencies and as air absorbs high frequencies more readily than low ones, the more delay there is between low frequencies and the higher harmonics of a sound, the sound becomes progressively more smeared and is perceived as more distant.

phase sync : In SMPTE timecode synchronization, an option by which the slave machine is speed-controlled in such a way that the phase of its bi-modulated sync tonecode wave is held in phase with the sync tonecode wave on the master machine. This provides much closer alignment of the two than just frame lock. However, because the synchronizer must make continuous adjustments to the slaveís speed, phase sync can introduce noticeable flutter when the audio machine is slaved to video. In some synchronizers, only sub-frame information is used to achieve interlock, yielding a 1/100 frame accuracy between machines.

phase-shifter/phaser : (1) Phasing is an effect on higher frequencies which make a whispering or ocean-like sound, produced by a device called a phaser, also called a phase-shifter. See flanging. (2) Originally one of the defined MIDI Controller Change messages. It was assigned to the parameter in a synthesizer which alters the depth of the effect described as phasing. More recently, this message has been reassigned as one of five generalized Effects Depth messages. See effects control.

phase reversal switch : A switch, usually found in a balanced line, that allows the user to interchange the two conductors, causing a 180 degree shift in phase of the signal. This is often a feature of recording consoles to allow the engineer to optimize the phase relationships of multiple microphones placed in close proximity to each other, i.e., mics likely to pick up substantially identical signals, such as on a drum kit. See phase cancellation.

phase-shift : An alteration of the phase in the partials of a tone. Virtually all signal processing devices will cause a certain amount of phase-shift, also called phase modulation, as none of them are completely phase linear. Phase-shift is a characteristic of a device and is the change in phase impressed on a signal that passes through the device. An electronic device will always add a time delay to an applied signal. If the time delay is constant on all frequencies, the phase-shift between the input and output of the device will be a linear function of frequency, and the device is called phase linear. Deviations from phase linearity are called phase-shift. Equalizers, in particular, exhibit large amounts of phase-shift. In a complex waveform, phase-shift will cause a distortion of the waveform, even though the frequency response curve may be perfectly flat. There is considerable controversy over whether the ear can detect this type of phase distortion. See also PIM.

phase reversal : (1) The condition where the connection in one channel of a stereo signal are reversed. This is most likely to happen at the loudspeaker, and results in phase cancellation, particularly apparent in the bass. (2) In electronic signals, changing the polarity of the signal from positive to negative or vice versa, thereby causing a reversal in polarity of the signal. When viewed on an oscilloscope, the waveform flips with respect to the time axis. Also called polarity reversal or phase inversion. See common mode, out-of-phase. The pair of loudspeakers on the left are in phase--the speaker cones cause compression and rarefaction the surrounding air in unison. Those on the right are out-of-phase, causing the air compression generated by one speaker to be cancelled by the rarefaction generated by the other.

phase reinforcement : The opposite of phase cancellation. An reinforcement of signal components resulting from combining phase coherent waveforms. When two waveforms are mixed, their harmonics are added. If these signals are not perfectly in- phase with each other, the amplitudes of the harmonic components differ at various times, (as determined by the phase relationship.) If the added harmonics have the same polarity, the signal is reinforced at those frequencies.

phase modulation : Also known as phase-shift. An alteration of the phase of partials of a signal. Virtually all signal processing devices will cause a certain amount of phase modulation, none of them being completely phase linear. See also PIM.

phase manipulation : A technique used by aural enhancers which realigns the relative phase of existing harmonics.

phase meter : An electronic circuit and display that compares two incoming signals and shows the phase difference between them.

phase- lock : See sync-lock.

phase-locked loop (PLL) : A closed-loop electronic circuit that automatically adjusts and locks the frequency of an oscillator to the correct frequency for receiving a signal. The PLL is the preferred FM detector circuit in commercial systems today as it requires no tuned circuits, hence does not require alignment. It normally has high amplification which produces a strong output audio signal. Since it does not respond to amplitude variations, it also provides limiting action.

phase inversion : See phase reversal.

phase invert : See phi."

phase linear : The ability of an audio device to pass a signal without causing phase-shift.

phase coherent : A condition encountered in the summation of two or more in-phase signals, in which the signals combine constructively, with little or no phase cancellation.

phase compensation : In some tape recorders, there is a special equalizer whose purpose is to minimize phase distortion.

phase distortion synthesis : A form of modulation synthesis in which the spectrum of a DCOís output signal is altered by modulating the DCOís clock frequency within each cycle, while the over-all frequency is kept constant. The oscillatorís clock frequency speeds up and slows down, producing rapid phase changes as the waveshape is alternately compressed and expanded (distorted) to fit within the regulated period. Popularized by the Casio CZ-series synthesizers.

Phase-Alternating Line : See PAL.

phase cancellation : An attenuation of signal components resulting from combining out-of-phase waveforms. When two waveforms are mixed, their harmonics are added. If these signals are out-of-phaseout of phase with each other, the amplitudes of the harmonic components differ at various times, (as determined by the phase relationship.) If the added harmonics have the same polarity, the signal is reinforced at those frequencies, and vice-versa. See phase distortion.

phase : Phase is defined as the time relationship between two corresponding points on a continuous wave, or the angular, or time, displacement between the voltage and current in an AC circuit. A sine wave signal is the simplest possible waveform and goes through 360˚ in one cycle, whereby it returns to its starting point. Another way of saying the same thing is that the signal has gone through 360˚ of phase angle, or phase change. The phase is actually a measure of time, 360˚ equaling one period of the signal. The time represented by a phase change of a certain number of degrees is thus dependent on frequency.

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