Which term describes the ratio of an amplifier's output to its input signal?

The term that describes the ratio of an amplifier's output to its input signal is referred to as system gain. System gain serves as a critical parameter in electroencephalographic (EEG) recordings because it quantifies how much an input signal, such as the electrical activity from the brain, is amplified by the system to produce a readable output.

Understanding system gain is essential in ensuring that the electrical signals from the electrodes are sufficiently increased for further analysis while maintaining signal integrity. A higher gain means that even small inputs are scaled up to a level that can be more easily interpreted, which is vital during EEG assessments.

The other terms, while relevant in their contexts, do not specifically convey the concept of output to input signal ratio. CMRR (Common Mode Rejection Ratio) pertains to the ability of an amplifier to reject input signals that are common to both input leads, rather than directly indicating the relationship between input and output levels. Display sensitivity refers to the ability of the display device to reflect changes in the input signal, and impedance concerns the resistance within the circuit but does not measure gain. Thus, system gain is the appropriate term to describe the ratio of an amplifier's output to its input signal.