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Entries found for search: modulation

Amplitude Modulation (AM) : The instantaneous amplitude modulation of one signal by another. This results in the formation of sidebands which contain the same information as the original signals, but translated upwards and downwards in frequency. In AM radio transmission, the audio signal is combined with a very high-frequency sine wave, called a carrier, in such a way that the amplitude of the carrier is varied in exact response to the amplitude and frequency of the signal. This is called the amplitude modulation of the carrier. The modulated carrier is transmitted at high power where it is received by radio sets that are tuned to the carrier frequency. The modulated carrier is then demodulated by a process called detection, recovering the original signal. In radio, a circuit that does amplitude modulation is also called a heterodyne.

Bass Intermodulation (BIM) : Bass intermodulation is a type of distortion caused by the modulation of audible frequencies by subsonic noise.

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.

modulation routing : The routing of a control voltage, either via hardware or software, from one module source to another.

frequency modulation (FM) : (1) A change in the frequency (pitch) of a signal. At low modulation rates, FM is perceived as vibrato or some type of trill. When the modulation wave is in the audio range, FM is perceived as a change in timbre. FM synthesizers, commonly found on soundcards, create sounds using audio-range frequency modulation. See FM synthesis. (2) Frequency modulation is the instantaneous changing of the frequency of a carrier in response to a modulation signal, usually an audio waveform. As the signal voltage varies up and down as it follows the waveform, the frequency of the carrier varies up and down from its nominal unmodulated value. The FM receiver is tuned to the carrier frequency, and the received signal, after suitable conditioning, is applied to a special circuit called an FM detector, also called a demodulator or discriminator, which recovers the audio signal. See amplitude modulation.

frequency modulation distortio : Examples of frequency modulation distortion are flutter and wow, and Doppler distortion caused by the motion of rotary (Leslie) loudspeaker cones.

intermodulation distortion : While harmonic distortion adds frequencies that are harmonically related, intermodulation distortion adds nonharmonic partials to the original signal. IM is a measure of how two frequencies that are present at the same time affect each other. Amplitude intermodulation distortion is caused when combinations of two or more frequencies generate new frequencies which are sums and differences of the original signal, i.e., the amplitude modulation of one signal by another. If an amplifier is used to amplify each tone equally, but if the gain of the amplifier varies with signal level (i.e., it is nonlinear), high-frequency sounds will be amplified by different amounts depending on whether a nearby low-frequency sound is near zero or near its peak. Therefore, the high-frequency signal will undergo changes in amplitude at the rate of the low-frequency signal, modulating the high-frequency sound which will be heard to flutter in the presence of the low-frequency sound. PIM is another component of intermodulation distortion, but to a lesser degree.

matrix modulation : A method of connecting modulation sources to destinations in such a way that any source can be sent to any combination of destinations.

modulation : (1) The process of sending a control signal to a sound source so as to change the character of the sound while the sound is playing. The modulation signal tells the receiving module to do something to the sound by changing one of its parameters in a predictable way. The place where a modulation signal originates is referred to as a modulation source. The place where the receiving module accepts the control signal is called a modulation input. For example, in a synthesizer, MIDI Velocity messages can be used to modulate the rolloff frequency of a filter. An envelope generator modulating an amplifierís amplitude setting causes the signalís level to change over time. (2) Changing a carrier signal in such a way as to carry information, e.g., amplitude or frequency modulation. (3) In music, a change of key. (4) The variation in the normally geometric groove on a record, which encodes the audio signal. (5) Electrically, another term for signal level, a usage typically encountered in England andin Europe. See overmodulation, undermodulation.

modulation module : See control module.

modulation noise : Noise which is present only in conjunction with a signal is called modulation noise. In analog tape recorders, the recording process has a certain granularity due to the fact that the magnetic characteristics of the tape are not completely uniform as the magnetic domains are of finite size. A recorded signal has an irregularity which sounds like the addition of noise. In digital audio systems, there is also an uncertainty in the level of the signal because of quantization error in the A/D converter. This uncertainty also sounds like added noise and is not present if the signal is not present. Compare with distortion. See Barkhausen effect, granularity.

modulation synthesis . See phase distortion synthesis.

modulation wheel : One of the defined MIDI Controller Change messages. Physically, the mod wheel most often appears as a wheel at the left side of a keyboard. When operated, it induces some effect such as vibrato, although its precise function varies from device to device and can often be programmed by the user. See real-time controller.

spectral gain intermodulation : The misuse of a (manual) compressor, set to high ratios and fast attack and release constants, producing loss of transients, loss of high-end, and other undesirable effects such as a kick drum ducking the vocals. The remedy for spectral gain intermodulation is to set a low threshold to bring low signals up, but also to be less extreme in the ratio, attack, and release settings. See also breathing.

pulse-width modulation : See PWM.

pulse-code modulation : See PCM.

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.

overmodulation : A situation which occurs when the amplitude of a signal exceeds the limits of the recording or broadcasting system. This causes distortion and can, in exceptional circumstances, damage equipment through which the signal passes. The opposite of undermodulation.

noise modulation See dither.

timbre modulation : A technique whereby a sample loop point length or position is changed via modulation, such as sweeping through a wavetable to produce an extreme stuttering effect.

undermodulation : A situation which occurs when the amplitude of a signal falls well below the optimum level in a recording or broadcasting system, causing it to be masked by noise. In digital systems, undermodulation can lead to distortion. See overmodulation.

waveform modulation : A voltage-controlled change in the timbre of a note or entire samplepatch, independent of the he pitch or frequency normally ybeing designated by the keystrokes. See sound synthesis, Appendix C.

delta modulation : In the UK, often, and more properly called delta-sigma modulation. A type of PCM which differs from most other digital encoding schemes in that the signal, after being sampled at a fast rate, is encoded as the difference between successive levels, rather than as the absolute level of each sample. Delta modulation requires a very high sampling rate, usually around 700kHz, but the digital words need for each step contain one bit, whereas conventional PCM samples at only about 45kHz but requires 14-16 bit words. The "delta" phase of delta modulation involves taking the difference of the reconstructed signal and the incoming signal to adjust the output to minimize the quantization error; the "sigma" part involves the summation of the differences to reconstruct the original signal, although there are a number of variant algorithms based on this basic theme. The reason for the popularity of delta modulation-type converters is the inherent linearity of the process. See also ADPCM.

delta-sigma modulation : See delta modulation.

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