If an equalization tap crosses the Echo Detection Threshold (NMTER), PreEQ can calculate the length of the echo cavity.
NOTE: Thresholds are not uniform across all taps. Those near the main tap should receive more energy than taps further away.
Echo cavity size is a calculated distance between equalized tap locations. If the decibel value exceeds the threshold (is closer to zero), PreEQ assumes an echo cavity exists. In the table below, echo cavity size predicts the presence of an echo cavity at a given decibel value.
| Size | Threshold | -37 dB | -27 dB | -17 dB | -7 dB |
|---|---|---|---|---|---|
| 0 to main tap | None, these values cannot cause echo cavities | No | No | No | No |
| +1 - +2 | Greater than -15 dB | No | No | No | Yes |
| +3 - +6 | Greater than -30 dB | No | Yes | Yes | Yes |
| +7 and beyond | Greater than -35 dB | No | Yes | Yes | Yes |