M(t), the sinusoidal 10hz modulator signal, C(t) the sinusoidal 220 Hz carrier signal, and A(t) the two combined using amplitude modulation.Įxpanding on amplitude modulation requires us to introduce more parameters and elements to the technique to give it some "weight" with other, more popular techniques. As a result, we find that AM and RM is used more often in signal processing than signal generation.įigure 8.4 A time-domain plot of an amplitude-modulated signal. Control over these generated partials may not, however, be as detailed and straightforward as techniques such as additive synthesis. Using a harmonically dense signal such as a square wave oscillator can create a wealth of sidebands from a minimum of control parameters and computation. One of the advantages of AM, like its cousin, RM, is that using just two signals or oscillators, we can create some partially rich signals. The two sidebands are sum and difference frequencies of the carrier and modulator, C and M, and have amplitudes at half the amplitude of the carrier signal. The difference between amplitude modulation and ring modulation is that in AM the carrier frequency is preserved and the sidebands generated are at half the amplitude of the carrier amplitude.įigure 8.3 The frequency-domain spectrum of an amplitude-modulated signal. The difference between the two techniques is highlighted here: Like ring modulation, amplitude modulation produces a pair of sidebands for every sinusoidal component in the carrier and modulator, and these sidebands are generated at frequencies the sum and difference of the two signal frequencies. Without mention of the unipolar modulator, this technique would appear to be identical to ring modulation. Where C is the carrier signal and M is a unipolar modulator, typically set to vary between values of 0 and 1. Each value of a carrier signal, C, is multiplied by a modulator signal, M, to create a new ring-modulated signal, R:
Ring modulation is the multiplication of two bipolar audio signals by each other. The reason for these two different types of signal follows. A unipolar signal is a bipolar signal that has been constant-shifted, that is, a constant value added to the overall signal to shift it into a range above zero, typically between 0 and 1. A bipolar signal is the type of signal we have been examining in previous chapters, it has both a negative and positive amplitude and the waveform generally "rests" around zero in a time-domain plot. In the two basic methods of modulation synthesis that occur, ring modulation and amplitude modulation, there are two unique types of signal that occur in each method: bipolar and unipolar signals. Modulation is typical in synthesis because it enriches the character of the sound and also adds to the variance in timbre / character over time which is so often found in nature.įigure 8.1 Unipolar (between 0 and 1) and Bipolar (between -1 and +1) waveforms. Modulation can be found in a range of different sound effects and synthesis techniques and some of these effects occur naturally and help us to identify certain types of sound for instance the commonly found performance styles of tremolo (modulation of amplitude) and vibrato (modulation of frequency) that are used in many stringed instruments are examples of this. When we talk about modulation from an audio synthesis point of view, we refer to a time-varying signal (the carrier) being affected in some way by another (the modulator).
0 kommentar(er)
