Amateur radio stations are required to have means of indicating or preventing a signal quality problem unique to voice transmissions. What is it?

When transmitting voice on amplitude-modulated modes, driving the microphone audio levels too high results in overmodulation. This distorts the signal and creates spurious emissions known as 'splatter,' which severely interfere with neighboring frequencies. To prevent this, regulations mandate that amateur stations have meters or internal circuits (like Automatic Level Control) to prevent overmodulation. It is the operator's responsibility to ensure their transmitter's audio gain is set correctly. While excessive compression or inadequate filtering can make a voice transmission sound poor or noisy, overmodulation is the specific technical problem that violates bandwidth rules and must be actively prevented by regulatory standards.