Definition: frequency response

In an audio system, the accuracy of sound reproduction. A totally flat response means that there is no increase or decrease in volume level across the frequency range. Measured in decibels (dB), this would be plus or minus 0 dB from 20Hz to 20,000Hz. A high-end audio system can deviate by +/- 0.5 dB, but a CD-ROM drive should not be off by more than +/- 3 dB.