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Some electronic signal generators produce waveforms using a method called direct digital synthesis. This involves constructing a signal from a series of digital samples that are stored in the signal generator's memory. A direct digital synthesizer contains a precise clock, phase comparator and register to control the position in the waveform, one or more memory devices that contain stored waveform data and a digital to analog converter (DAC) to produce the output. The memory contains data for specific periodic waveforms that may include simple sinusoids or other common functions like triangular waves. At each transition of the clock, the phase comparator and register step through the signal period and determine the memory address where that point is defined. The identified memory address sends a waveform value to the DAC, which produces the analog output. National Instruments states that its function generators have a resolution of less than 0.4 microHertz. For a one MegaHertz signal, this represents a frequency precision of better than two parts per trillion. Direct digital synthesis is used in function generators to produce signals with precise frequencies and phases. These devices can also be swept in frequency very precisely and are therefore useful for applications like the testing of filters.Design
Waveform Types
Operation
Precision
Uses
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by karlasim123 on November 30th, 2010
In the 1960s, Robert Moog developed what is known today as the musical synthesizer. Moog's synthesizer was an analog device that manipulated sound with mechanical dials and sliding knobs. Although the sounds these early synthesizers created were similar to what modern synthesizers produce, there was no way to record and store the setting for a particular sound except write down the numbers for each control. Digital technology in the 1980s changed the synthesizer as the sounds were not only more precise, but also easily stored.
Digital
Direct digital synthesizers differ from analog devices because computer generated electrical impulses produce the sound. Digital means the computer can produce two settings: on and off. Multiple on and off settings turned on and off in a particular sequence will activate a sound speaker and produce the sound. Although a computer generates the sound it is not artificial in any way; just as an electric guitar turns string vibrations into electric current to activate a speaker, so does a direct digital synthesizer.
Waves
Sound is a wave traveling through the air. All sound has three kinds of wave shapes: a saw-tooth wave, a round wave and the two combined into a square wave. Saw-tooth waves are buzzing sounds, round waves are singing sounds and square waves are percussion sounds like a drum. A direct digital synthesizer has three wave generating components to produce these different sounds. Combining different wave speeds (frequency) and sizes (wavelength) produces the range of sounds from brass instruments to winds to robots and birds singing.
Volume
The synthesizer also digitally controls the volume. Volume not only determines how loud a sound is but also how the listener perceives the sound. Varying volume over the course of just one quick sound is the difference between a sharp yell and a rising and quieting cry. Digital synthesizers are able to control the volume of each sound with several variations in the course of less than one second on the clock.
Pitch
Pitch is the difference between high notes and low notes. The wave generator in the direct digital synthesizer responds to commands from the individual keys on the keyboard. Each key alters the wave frequency and produces a different note.
Envelope
All the components of the direct digital synthesizer are brought together in what is known as an envelope: attack, decay, sustain and release, known as ADSR. Each part of the ADSR envelope is controlled by the computer in the direct digital synthesizer. Once all the variations in the wave form, volume and ADSR envelope are determined, the settings are saved with a computer program number. Any time a musician wants to use the same sound for a certain song, the program number is accessed and the direct digital synthesizer is ready to play.
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