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Modulation Synthesis

Modulation Synthesis. Amplitude and Ring Modulation. Modulation. In electronic and computer music terms, modulation means that some aspect of one signal (the carrier ) varies according to an aspect of a second signal (the modulator )

brendan-kemp
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Modulation Synthesis

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  1. Modulation Synthesis Amplitude and Ring Modulation

  2. Modulation • In electronic and computer music terms, modulation means that some aspect of one signal (the carrier) varies according to an aspect of a second signal (the modulator) • Although this definition would seem to apply to any signal that makes use of an amplitude or pitch envelope, we usually exclude such instances. • When the modulating frequency rises into the audio domain (above 20 Hz), audible frequency components, called sidebands, appear.

  3. Ring and Amplitude Modulation • Ring Modulation and Amplitude modulation both involve multiplying the amplitude of two audio signlas. • Ring Modulation (RM): both signals are bipolar, with their amplitudes fluctuating relatively equally in positive and negative directions. • Amplitude Modulation (AM): the modulating signal is unipolar, meaning it only fluctuates in one direction away from zero (positive amplitude usually). • Bipolar signals can be offset (amplitude addition) to become unipolar • Direct Current (DC) offset

  4. Ring Modulation • RMt = Ct x Mt (analog equation) • RMn = Cn x Mn (digital) • Multiply signal outputs (amplitudes) • Sidebands at Cfreq Mfreq • Carrier is suppressed (eliminated) • What happens to negative frequencies? • A negative frequency is the same as a positive frequency with inverted amplitude. • Zero amplitude in either signal will cause modulated output to have zero amplitude.

  5. Amplitude Modulation • Same equation as RM • AMn = Cn x Mn • Where M is a signal that varies between 0 and 1 in amplitude. • Sidebands at Cfreq + (Cfreq Mfreq). (carrier present) • Integer C:M ratios produce harmonic spectra.

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