An equalization curve established by the RIAA and applied to all music as it is transferred from master tape to master disc. This pre-emphasis curve introduces a 20dB skew in the frequency content of the program, decreasing the bass content and increasing treble over a 500Hz threshold. The complementary opposite de-emphasis is applied by the phonograph preamplifier during reproduction. Since groove width increases in proportion to the low-frequency content of the program, and since vinyl disc surface noise is most noticeable in the high frequencies, the RIAA curve is designed to enable more dense program recording while minimizing the effect of surface noise.