Group Delay

Group delay converts the abstract concept of phase shift into a tangible quantity: time. While a phase plot might show a confusing tangle of wrapped angles, the corresponding group delay plot clearly shows that low frequencies are delayed by X milliseconds and high frequencies by Y milliseconds. This makes group delay the preferred metric for evaluating time-domain behavior. For a minimum-phase system, the group delay is entirely determined by the magnitude response. Peaks in the magnitude response (resonances) create peaks in the group delay — the system "rings" at those frequencies, keeping energy for longer. A sharp null in the response creates a group delay anomaly. This relationship means that any equalization that flattens the magnitude response will also smooth the group delay. In loudspeaker measurement, group delay reveals driver-to-driver alignment issues and crossover artifacts. A well-aligned two-way speaker might show 1-2 ms of excess group delay at the crossover frequency. Poorly aligned systems can show 5-10 ms jumps, which cause smearing of transients. Subwoofer alignment is particularly critical: at 80 Hz, a quarter wavelength is about 1 meter, so even small timing errors create significant cancellation. Group delay perception thresholds vary with frequency. At low frequencies (below 200 Hz), listeners can tolerate 10-20 ms of group delay variation without audible degradation. Above 1 kHz, the threshold drops to 1-2 ms. This frequency-dependent sensitivity means that perfect time alignment across the entire audio band, while theoretically ideal, is not always necessary. Negative group delay can occur at frequencies near sharp nulls or at the edges of bandpass filters. This does not violate causality — it means the group of frequencies near the null arrives slightly early relative to the overall system delay. SonaVyx computes group delay from the unwrapped phase of the transfer function measurement.