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Analog 'O'
vs Digital 'O'
Are They The Same?

by

Bud Bremner

previously published in
Professional Sound Magazine

In mastering, many digital masters are submitted with different regard to audio levels and their relative reference level tones. While there is no officially recognized standard that bridges the two, many audio engineers (including the author) have found a few simple rules that work well. Most engineers already know these but for those who are just starting out, here are a few points.

Do not put a 1khz tone at 'O' digital full scale. A tone at this level will be from 12 to 16 db higher than it should be, it has virtually no relationship to the RMS audio value that it's supposed to represent and is brutal on your speaker cones and signal path not to mention your ears. Can you imagine audio levels hovering nicely around O VU, preceded by this killer 1 khz tone ripping your ears off at +15 VU? It happens!

A level reference tone on a DAT, just like on an analog recorder, is supposed to represent RMS audio values, not peak values. On a DAT recorder, a respectable RMS audio value and it's level reference tone will be around -12 to -16 ppm (peak program meter). Tracking usually requires more headroom so -14 to -16ppm or 14 to 16 decibels below digital full scale works well. Example: your analog 'O' VU reference tone would appear at -14 ppm, leaving a margin of 14 db of peak headroom above O VU. Mastering engineers utilize tighter dynamics control so a margin of -10 to -12 ppm is usually enough. Now, after all that I'm going to tell you that tones of any kind are not necessary for DAT recording.

The use of 10khz and 50hz/100hz tones are also not necessary for DAT recording. These tones are used for azimuth alignment, and high and low frequency playback equalization on analog tape recorders. Such alignment is not user definable on DAT recorders so using these tones might send the wrong message regarding your experience with digital recording.

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