Tape Recording Calibration and Metering

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Accurate calibration of a tape based recording is necessary to match record and replay levels, and is critical for Dolby tracking.

Reference:

Recorded Flux

  • 3% distortion is generally considered maximum acceptable.
  • MOL (Maximum Output Level):
    • Level that produces 3rd harmonic distortion of 3%
    • Frequency dependent. At high frequencies can't be used as harmonics won't be reproduced.
  • SOL (Saturated Output Level):
    • The level which produces the maximum output. More record level reduces playback output.
  • Measurement of flux can be open circuit or closed circuit
    • 200 nWb/m closed circuit = 220 nWb/m open circuit (Dolby Level)

Metering

Three standards:

  • DIN
    • 0 dB is 250 nWb/m
    • Dolby level shown at -1.2 dB
    • Used by Marantz, Sony, TEAC
  • Nakamichi
    • 0 dB is 200 nW/m
    • Dolby level shown at 0 dB
  • Old Philips
    • 0 dB is 160 nWb/m
    • Dolby level shown at 2.8 dB
    • Most common, used by Aiwa, Akai, Pioneer, Technics, etc

True VU Meters have a tightly controlled professional definition of response, but are more approximate in consumer grade equipment. They show an average signal level over time, and smooth out sharp peaks.

  • 3 % distortion level is usually around +6 to +8 VU

Peak Meters have fast response, showing peak levels. Better for use on cassette decks with their lower headroom compared to faster tape speeds of Open Reel decks.

  • Generally 0 dB on a VU meter is a lower flux level than 0 dB on a peak meter, by about 3 dB.