Preamplifiers boost very weak signals and transmit them to standard amplifiers. A preamplifier prepares signals from devices like microphones and instrument pickups, which are often susceptible to noise and other sources of signal interference, for processing, ensuring the final signal is clear enough for analysis. Desirable qualities in preamplifiers include linearity (constant gain throughout range of operation), high input impedance (meaning only a negligible amount of current is necessary to sense an input signal), and low output impedance (stability in output voltage when current is drawn). Noise performance is also a key characteristic, as to be analyzed a signal needs to resist. Preamplifiers, also known as preamps, are ideal test instruments for enhancing measurement system sensitivity in EMC testing and other applications that call for low noise and high signal amplification. Troubleshooting and debugging as part of the radiated emissions portion of EMC testing in particular often calls for preamplifiers to amplify signals otherwise immune to analysis.