Tape Recording Calibration and Metering

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

Reference:

• Walkman Archive
• Marantz Reference
• BASF Reference
• Wikipedia - Tape Formulations

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 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.