NullDurchschreitdetektoren

NullDurchschreitung, commonly referred to in English as zero crossing, is a concept in signal processing and measurement describing the moments when a waveform passes through the zero-amplitude axis. It is most relevant for alternating or time-varying signals, including electrical voltages, audio signals, and sensor outputs.

Zero-crossing detection involves identifying the instants where the signal changes sign, from positive to negative or vice versa. In analog implementations, a comparator with a zero reference, sometimes equipped with hysteresis via a Schmitt trigger, produces clean transition pulses at each crossing. In digital systems, zero crossings are detected by comparing successive samples and recording an edge whenever the sign of the sample changes.

Applications of zero-crossing detection include frequency estimation, phase synchronization in phase-locked loops, and timing for switching electronics to reduce EMI by synchronizing switching events to waveform crossings. In communications, zero-crossing timing helps in demodulation schemes that rely on axis crossings rather than full amplitude information.

In audio and speech processing, the zero-crossing rate—the number of sign changes per unit time—serves as a simple feature for voice activity detection, speaker identification, and some forms of pitch estimation. However, zero crossing can be sensitive to noise and waveform distortion; near-zero offsets, noise, or DC components can cause spurious crossings. Remedies include input conditioning, high-pass filtering to remove DC, and adding hysteresis to detectors.

Variants of this concept appear in various languages, with German literature often using Nulldurchgang or Nulldurchschreiten to describe the same phenomenon.