In its most basic form a lock-in amplifier is an instrument with dual capability. It can recover signals in the presence of an
overwhelming noise background or, alternatively, it can provide high resolution measurements of relatively clean signals over
several orders of magnitude and frequency. However, modern instruments offer far more than these two basic functions and this
increased capability has led to their acceptance, in many scientific disciplines, as units which can provide the optimum solution to a
large range of measurement problems. For example, the modern lock-in amplifier will function as: