Density-response and modulation-noise testing of digital magnetic recording tapes

Density response and modulation noise are key factors in the high-density performance of magnetic recording tapes, but are difficult so measure independently because of velocity variations and nonstationary statistics. Several measurement methods and their deficiencies are reviewed. Demodulation removes the velocity variation effect, enabling separation of the signal from the noise; and data acquisition with a microcomputer enables measurement of tapes having unusual variations along their length. An experimental test unit is described, giving sample results from several commercial tape types. Slope of the dB density response, or the effective magnetic separation (EMS) is the best indicator of tape performance at high density.