Which system modification primarily enhances the signal for better clarity in ultrasonic testing?

The enhancement of signal clarity in ultrasonic testing is primarily achieved through the use of receiver-amplifier circuits. These circuits play a critical role in the process as they amplify the weak signals received from the ultrasonic transducer, allowing for better detection and analysis of the signals that return after interacting with the material being tested. By improving the amplitude of these signals, the circuits ensure that even the faint echoes generated from flaws or features within the material can be clearly interpreted by the system. This amplification is crucial for distinguishing between relevant signals and background noise, allowing for more accurate assessments.

In contrast, other options like pulses refer to the initial signal sent out by the transducer, while clock adjustments pertain to timing mechanisms and aren't directly responsible for clarity. High-frequency filtration can help eliminate noise, but it does not directly amplify the signal in the same way that receiver-amplifier circuits do. Therefore, the significance of receiver-amplifier circuits lies in their essential function of increasing signal strength to provide clarity in the interpretation of ultrasonic test results.