Phase offset modulation works by overlaying two instances of a periodic waveform on top of each other. (In software synthesis, the waveform is usually generated by using a lookup table.) The two instances of the waveform are kept slightly out of sync with each other, as one is further ahead or further behind in its cycle. The values of both of the waveforms are either multiplied together, or the value of one is subtracted from the other.
In electronics, acoustics, and related fields, the waveform of a signal is the shape of its graph as a function of time, independent of its time and magnitude scales and of any displacement in time.
A software synthesizer, also known as a softsynth, or software instrument is a computer program, or plug-in that generates digital audio, usually for music. Computer software that can create sounds or music is not new, but advances in processing speed now allow softsynths to accomplish the same tasks that previously required the dedicated hardware of a conventional synthesizer. Softsynths are usually cheaper and more portable than dedicated hardware, and easier to interface with other music software such as music sequencers.
In computer science, a lookup table is an array that replaces runtime computation with a simpler array indexing operation. The savings in terms of processing time can be significant, since retrieving a value from memory is often faster than undergoing an "expensive" computation or input/output operation. The tables may be precalculated and stored in static program storage, calculated as part of a program's initialization phase (memoization), or even stored in hardware in application-specific platforms. Lookup tables are also used extensively to validate input values by matching against a list of valid items in an array and, in some programming languages, may include pointer functions to process the matching input. FPGAs also make extensive use of reconfigurable, hardware-implemented, lookup tables to provide programmable hardware functionality.
This generates an entirely new waveform with a drastically different shape. For example, one sawtooth (ramp) wave subtracted from another will create a pulse wave, with the amount of offset (i.e. the difference between the two waveforms' starting points) dictating the duty cycle. If you slowly change the offset amount, you create pulse-width modulation.
The sawtooth wave is a kind of non-sinusoidal waveform. It is so named based on its resemblance to the teeth of a plain-toothed saw with a zero rake angle.
A pulse wave or pulse train is a kind of non-sinusoidal waveform that includes square waves and similarly periodic but asymmetrical waves. It is a term common to synthesizer programming, and is a typical waveform available on many synthesizers. The exact shape of the wave is determined by the duty cycle of the oscillator. In many synthesizers, the duty cycle can be modulated for a more dynamic timbre. The pulse wave is also known as the rectangular wave, the periodic version of the rectangular function.
A duty cycle or power cycle is the fraction of one period in which a signal or system is active. Duty cycle is commonly expressed as a percentage or a ratio. A period is the time it takes for a signal to complete an on-and-off cycle. As a formula, a duty cycle (%) may be expressed as:
Using this technique, not only can a ramp wave create pulsewidth modulation, but any other waveform can achieve a comparable effect.
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Related Research Articles
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. Most radio systems in the 20th century used frequency modulation (FM) or amplitude modulation (AM) for radio broadcast.
Subtractive synthesis is a method of sound synthesis in which partials of an audio signal are attenuated by a filter to alter the timbre of the sound. While subtractive synthesis can be applied to any source audio signal, the sound most commonly associated with the technique is that of analog synthesizers of the 1960s and 1970s, in which the harmonics of simple waveforms such as sawtooth, pulse or square waves are attenuated with a voltage-controlled resonant low-pass filter. Many digital, virtual analog and software synthesizers use subtractive synthesis, sometimes in conjunction with other methods of sound synthesis.
The amplitude of a periodic variable is a measure of its change over a single period. There are various definitions of amplitude, which are all functions of the magnitude of the difference between the variable's extreme values. In older texts the phase is sometimes called the amplitude.
A signal generator is an electronic device that generates repeating or non-repeating electronic signals in either the analog or the digital domain. It is generally used in designing, testing, troubleshooting, and repairing electronic or electroacoustic devices, though it often has artistic uses as well.
Pulse width modulation (PWM), or pulse-duration modulation (PDM), is a method of reducing the average power delivered by an electrical signal, by effectively chopping it up into discrete parts. The average value of voltage fed to the load is controlled by turning the switch between supply and load on and off at a fast rate. The longer the switch is on compared to the off periods, the higher the total power supplied to the load. Along with MPPT maximum power point tracking, it is one of the primary methods of reducing the output of solar panels to that which can be utilized by a battery. PWM is particularly suited for running inertial loads such as motors, which are not as easily affected by this discrete switching. Because they have inertia they react slower. The PWM switching frequency has to be high enough not to affect the load, which is to say that the resultant waveform perceived by the load must be as smooth as possible.
Wavetable synthesis is a sound synthesis technique used to create periodic waveforms. Often used in the production of musical tones or notes, it was developed by Wolfgang Palm of Palm Products GmbH (PPG) in the late 1970s and published in 1979, and has since been used as the primary synthesis method in synthesizers built by PPG and Waldorf Music and as an auxiliary synthesis method by Ensoniq and Access. It is currently used in software-based synthesizers for PCs and tablets, including apps offered by PPG and Waldorf, among others.
A power inverter, or inverter, is an electronic device or circuitry that changes direct current (DC) to alternating current (AC).
Continuous phase modulation (CPM) is a method for modulation of data commonly used in wireless modems. In contrast to other coherent digital phase modulation techniques where the carrier phase
abruptly resets to zero at the start of every symbol, with CPM the carrier phase is modulated in a continuous manner. For instance, with QPSK the carrier instantaneously jumps from a sine to a cosine whenever one of the two message bits of the current symbol differs from the two message bits of the previous symbol. This discontinuity requires a relatively large percentage of the power to occur outside of the intended band, leading to poor spectral efficiency. Furthermore, CPM is typically implemented as a constant-envelope waveform, i.e., the transmitted carrier power is constant.
Therefore, CPM is attractive because the phase continuity yields high spectral efficiency, and the constant envelope yields excellent power efficiency. The primary drawback is the high implementation complexity required for an optimal receiver.
Power electronics is the application of solid-state electronics to the control and conversion of electric power.
A function generator is usually a piece of electronic test equipment or software used to generate different types of electrical waveforms over a wide range of frequencies. Some of the most common waveforms produced by the function generator are the sine wave, square wave, triangular wave and sawtooth shapes. These waveforms can be either repetitive or single-shot. Integrated circuits used to generate waveforms may also be described as function generator ICs.
Delta-sigma modulation is a method for encoding analog signals into digital signals as found in an analog-to-digital converter (ADC). It is also used to convert high bit-count, low-frequency digital signals into lower bit-count, higher-frequency digital signals as part of the process to convert digital signals into analog as part of a digital-to-analog converter (DAC).
The Korg DW-8000 synthesizer was an eight-voice polyphonic hybrid digital-analog synthesizer 61-note keyboard instrument released in 1985. By the time of its launch Korg had already begun a common trend in 1980s synthesizer design: using numerical codes to access or change parameters with the Korg Poly-61, which was widely regarded as the company's first 'knobless' synthesizer. This was a move away from the heavily laden, complex control panels of earlier designs.
An arbitrary waveform generator (AWG) is a piece of electronic test equipment used to generate electrical waveforms. These waveforms can be either repetitive or single-shot in which case some kind of triggering source is required. The resulting waveforms can be injected into a device under test and analyzed as they progress through it, confirming the proper operation of the device or pinpointing a fault in it.
Phase-fired control (PFC), also called phase cutting or "phase angle control", is a method for power limiting, applied to AC voltages. It works by modulating a thyristor, SCR, triac, thyratron, or other such gated diode-like devices into and out of conduction at a predetermined phase of the applied waveform.
The Korg DSS-1 is a 12-bit polyphonic sampling synthesizer released in September 1986. It came out at a time when many of the popular synthesizer companies were beginning to get into sampling, an area of sound design that had previously been left to a handful of fledgling companies such as Fairlight, E-mu, and Ensoniq. Like Yamaha and Casio, however, Korg did not stay long in the sampling arena. The DSS-1 was the company's only sampler until 1998 when Korg introduced sampling options on their Triton and Trinity series of workstations, and on their Electribe series of drum-and-phrase samplers.
Squarewave voltammetry (SWV) is a form of linear potential sweep voltammetry that uses a combined square wave and staircase potential applied to a stationary electrode. It has found numerous applications in various fields, including within medicinal and various sensing communities.
A digital signal is a signal that is being used to represent data as a sequence of discrete values; at any given time it can only take on one of a finite number of values. This contrasts with an analog signal, which represents continuous values; at any given time it represents a real number within a continuous range of values.
Pulse-density modulation, or PDM, is a form of modulation used to represent an analog signal with a binary signal. In a PDM signal, specific amplitude values are not encoded into codewords of pulses of different weight as they would be in pulse-code modulation (PCM); rather, the relative density of the pulses corresponds to the analog signal's amplitude. The output of a 1-bit DAC is the same as the PDM encoding of the signal. Pulse-width modulation (PWM) is a special case of PDM where the switching frequency is fixed and all the pulses corresponding to one sample are contiguous in the digital signal. For a 50% voltage with a resolution of 8-bits, a PWM waveform will turn on for 128 clock cycles and then off for the remaining 128 cycles. With PDM and the same clock rate the signal would alternate between on and off every other cycle. The average is 50% for both waveforms, but the PDM signal switches more often. For 100% or 0% level, they are the same.
