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:
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.