Synthetic instrument
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A synthetic instrument is a term in test and measurement science or metrology. A Synthetic Instrument is software that runs on a Synthetic Measurement System to perform a specific synthesis, analysis, or measurement function. A Synthetic Measurement System (SMS) is a common, general purpose, physical hardware platform that is intended to perform many kinds of synthesis, analysis, or measurement functions using Synthetic Instruments.
Typically the generic SMS hardware is dual cascade of three subsystems: digital processing and control, A/D or D/A conversion (codec), and signal conditioning. One cascade is for stimulus, one for response. Sandwiched between them is the device under test (DUT) that is being measured.
The term synthetic instrument is the opposite of the retronym natural instrument. Although the word “synthetic” in the phrase synthetic instrument might seem to imply that synthetic instruments are synthesizers: that they only do synthesis. This is incorrect. When we say synthetic instrument, we are saying that the instrument itself is being synthesized; nothing is implied about what the instrument itself does. A synthetic instrument might indeed be a synthesizer, but it could just as easily be an analyzer, or some hybrid of the two.
Synthetic instruments are implemented on generic hardware. This is probably the most salient characteristic of a synthetic instrument. Generic means that the underlying hardware is not explicitly designed to do the particular measurement. Rather, the underlying hardware is explicitly designed to be general purpose. Measurement specificity is encapsulated in software. Application software packages such as Measure Foundry are available to support the specific measurements required of the hardware.
An exact analogy to this relationship between specific measurement hardware versus generic hardware is the relationship between specific digital circuits and a general purpose CPU. A specific digital circuit can be designed and hardwired with digital logic parts to perform a specific calculation. Alternatively, a microprocessor (or, better yet, a gate array) could be used to perform the same calculation using appropriate software. One case is specific, the other generic, with the specificity encapsulated in software.
Synthetic instruments in test and measurement are conceptually related to the software synthesizer in audio or music. A musical instrument synthesizer synthesizes the sound of specific instruments from generic hardware. Of course, a significant difference in these concepts is that musical instrument synthesizers typically only generate musical sound, whereas a synthetic instrument in test and measurement may be equally likely to generate or to measure some signal or parameter.
A similar term commonly used in test and measurement, Virtual instrumentation, is a superset of synthetic instrumentation. All synthetic instruments are virtual instruments; however, the two terms are different when virtual instrument software mirrors and augments non-generic instrument hardware, providing a soft front panel, or managing the data flow to and from a natural instrument. In this case, the PC and accompanying software is supplementing the analysis and presentation capabilities of the natural instrument.
The essential point is this: synthetic instruments are synthesized. The whole is greater than the sum of the parts. To use Buckminster Fuller's word, synthetic instruments are synergistic instruments. Like a triangle is more than three lines, synthetic instruments are more than the triangle of hardware (Control, Codec, Conditioning) they are implemented on.
Therefore, one way to tell if you have a true synthetic instrument is to examine the hardware design alone and to try to figure out what sort of instrument it might be. If all you can determine are basic category facts, like the fact that it can be categorized as a stimulus or response instrument, but not anything about what it's particularly designed to create or measure—if the measurement specificity is all hidden in software—then you likely have a true synthetic instrument.
