A comparison of several methods of measuring noise in magnetic recorders for audio applications

The various methods of measuring noise in audio magnetic recorders are discussed, and data are shown comparing the numbers observed for the different methods (IRE Standard Methods, and others) when applied to the same recorder. This data will enable one to compare other data taken by one method with data taken by another method. The present audio specifications based only on broad-band noise are shown to be inadequate, as the equipment noise in the range of low hearing sensitivity masks any improvements which may be made in tape noise, or with the Ampex Master Equalization. A measure of relative audible noise level should be added to the present broad-band measurement.