Why EQ exists
Heads and tape do not record and reproduce every frequency equally. Standardised recording and playback characteristics allow tapes to be exchanged between machines.
THE ENCYCLOPEDIA / 04
NAB & CCIR / IEC
The correct curve restores the intended tonal balance.
Match the tape
Use the EQ specified for that recording and speed. The wrong curve changes tonal balance. A tone control is not a substitute for correct playback equalisation.
Two meanings of NAB
NAB equalisation is an electrical standard. A NAB adapter is a mechanical reel fitting. Owning one says nothing about the other.
Common stereo replay settings
| Speed | NAB / IEC2 | IEC1 / often called CCIR |
|---|---|---|
| 7½ ips | 3180 + 50 µs | ∞ + 70 µs |
| 15 ips | 3180 + 50 µs | ∞ + 35 µs |
In practice
Which sounds better?
Use the standard the tape was recorded for. IEC1 at 15 ips has technical advantages with modern tape, but changing a NAB tape to IEC playback does not convert its recording.
My machine has no switch. What now?
Consult its manual and service configuration. Some machines have fixed EQ or internal options. Conversion needs correct electronics and alignment, not just a new front-panel label.
Does EQ define recording level?
No. EQ and reference fluxivity are separate settings. A tape can use NAB with various reference levels, or IEC with various levels.