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Entries found for search: transform

isolating transformer : A transformer, typically with equal primary and secondary coils used to provide power to a piece of electrical or electronic equipment. The lack of a direct connection between the primary power source and the secondary load improves the safety factor for the user of the equipment.

line-matching transformer : An electronic component that matches the output impedance of one device with the input impedance of the next device in a signal path.

matching transformer : Short for an impedance-matching transformer. Used to interconnect devices or cables of different impedances. Necessary, for example, when using a low-impedance microphone with a guitar amplifier, which has high-impedance inputs. The transformer increases the energy transfer between the microphone and the input, preserving the high-frequency response in the signal.

transform coding : Used in Dolby AC-2 and MPEG codecs, whereby an input signal is analyzed within the frequency domain as a series of narrow bands,; e.g., an AC-2 encoder/decoder uses 256 narrow bands. Frequency-masked bands whose information is inaudible because of sustained tones or transients will be ignored by such systems, thereby enabling the compression algorithm to concentrate its bit allocation on those bands which contain subjectively relevant information. In addition, transform-based systems use a system of predefined waveform patterns from an established "wavelook-up" tablelibrary of sound models and send only the identity code to the decoder to "resynthesize" the closest-fit library model. As opposed to, for example, ADPCM.

transformer : A device consisting of two or more coils of wire wound on a common core of soft iron or other magnetically permeable material. The number of turns in one coil divided by the number of turns in the other one is called the turns ratio. An alternating voltage across one coil will appear across the other coil multiplied by the turns ratio.

transformerless input : On an audio device, an input which does not use a transformer for impedance-matching. Such inputs will make use of semiconductors such as transistors, and may be described as active inputs. Their main advantage is a saving in size, although some argue that they give better performance than transformers, the truth of the assertion probably depending most on the quality of the device, rather than its type.

Perceptual sub band/transform : Codecs designed to reduce the data rate and/or size of a digital audio file. The encoder applies a psychoacoustic model to estimate whether, in any particular band of frequencies, the signal strength in that band I above or below the perceptual threshold relative to adjacent frequency bands. If the signal is above that masking threshold, than a spectral coefficient or value is generated to represent the signal in that band and the coefficient becomes the stand-in, or representation of, the actual audio in that band, if the signal is not above the predicted masking threshold, then that band of frequencies is tossed out to reduce the final size of the essence.

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