In electronics and computing, analog synthesis refers to a technology based on which of the following principles?

Introduction / Context:
In audio technology and electronic music, the terms analog and digital describe two different ways of representing and generating signals. Analog synthesis was widely used in early synthesizers and still has an important place in sound design. Understanding what makes a system analog helps in distinguishing it from digital sampling or purely numerical processing. This question focuses on the basic principle behind analog synthesis technology.

Given Data / Assumptions:

• The context is synthesis of signals or sounds in electronics and computing.
• Four descriptions are given, some relating to digital sampling and some to analog representation.
• Analog systems use continuous physical quantities, while digital systems use discrete numbers.
• We are looking for the statement that best captures the analog principle.

Concept / Approach:
Analog synthesis involves generating and processing electrical signals that vary continuously in time and amplitude. These signals directly correspond to physical quantities such as voltage or current in circuits. In contrast, digital systems represent signals as sequences of numbers and operate using discrete steps. Sample based synthesis that stores brief digital recordings is a digital technique, even if controlled by a keyboard. Interfacing equipment is a general concept that does not define analog representation. Therefore, the correct description of analog synthesis is one that mentions representing data as measurable physical quantities that can vary in a continuous range.

Step-by-Step Solution:
Step 1: Recall that in analog electronics, information is carried by continuous signals, such as a voltage that can take any value within a range, not just fixed levels. Step 2: In analog synthesizers, oscillators, filters, and amplifiers shape electrical waveforms that correspond directly to the sound waves produced by speakers. Step 3: Recognise that placing short digital recordings under keyboard control is sample based digital synthesis, not analog synthesis. Step 4: Interfacing synthesizer equipment is related to connectivity and control but does not define the fundamental nature of analog representation. Step 5: Identify that representing data in terms of measurable physical quantities that vary continuously is the essence of analog technology, making this the correct option.

Verification / Alternative check:
Definitions of analog systems in standard electronics texts describe them as systems where signal variables are continuous in both time and amplitude and directly relate to the physical quantity being measured or generated. In contrast, digital systems are defined by discrete time and amplitude levels and representation using numbers. Sound synthesizers that use voltage controlled oscillators and filters are classic analog devices, matching the idea of continuous physical representations.

Why Other Options Are Wrong:
Placing short digital recordings under keyboard control: This is sample based digital synthesis, not analog synthesis. Interfacing multiple synthesizer devices: This is about connectivity and control, not how signals are represented internally. Representing physical quantities as discrete numbers only: This describes digital systems, not analog systems.

Common Pitfalls:
Students may think that any system related to music synthesis is analog if it uses knobs and keys, but the real difference lies in how signals are represented and processed. Another confusion is to equate analog with old and digital with new, which does not help conceptually. Always focus on continuity versus discreteness when deciding whether a system is analog or digital.

Final Answer:
Analog synthesis is based on representing data in terms of measurable physical quantities that vary continuously.