The ratio of the received strength of a signal on a pair of wires to the amount of crosstalk between the wires.
The higher the attenuation to crosstalk ratio (ACR) for a given cable, the less chance of signal errors. ACR is calculated as the difference between the attenuation value and the near-end crosstalk value at a specific frequency.
This is because both attenuation and crosstalk are usually expressed in units of decibels for cabling media. The decibel scale is logarithmic in nature, which means that a difference in decibel values corresponds to a ratio of actual signal voltage or power levels.
For copper category 5 cabling, the ACR value is typically about 10 dB, at a frequency up to about 100 MHz. This value decreases slightly with increasing frequency until crosstalk and attenuation values converge, at which point transmission becomes error prone and the cabling ineffective for communication.