A difference amplifier, a crucial component in numerous electronic devices, ideally amplifies only the difference-mode signal, which is the difference between two input signals. However, in practical circuits, the output voltage depends on both the differential gain and the common-mode gain.

The ratio of differential gain to the common-mode gain is defined as the common-mode rejection ratio (CMRR). This ratio quantifies the ability of operational amplifiers (op-amps) to reject common-mode signals, which are identical signals present at both inputs of the amplifier.

For instance, consider a sound system where an op-amp picks up both music and electrical noise. A high CMRR allows the op-amp to effectively ignore the noise and amplify only the music, enhancing the sound quality of the system.

Another crucial characteristic of op-amps is the gain-bandwidth product. This is the product of the op-amp's open-loop voltage gain and the frequency at which this gain is measured. It remains constant for any given op-amp, providing a useful parameter for comparing the performance of different op-amps.

A unity gain buffer, or voltage follower, is a specific configuration of an op-amp that provides a voltage gain of one. This means that the output voltage matches the input voltage. It has low output impedance and high input impedance, making it ideal for signal isolation and impedance matching.

In an audio system, a voltage follower plays a vital role in preventing a low-impedance speaker from effectively shorting the audio signal from a high-impedance source to the ground. By matching the impedance levels, it ensures that maximum power is transferred from the source to the speaker without distortion or loss.

In conclusion, understanding the characteristics and functionalities of op-amps, such as the CMRR, gain-bandwidth product, and unity gain buffer configuration, is essential in designing effective and efficient electronic systems. These principles form the backbone of many modern audio and communication systems, influencing their performance and quality.