Tape Notes · Tape knowledge

Reading a blank tape's J-card: MOL, SOL, bias, EQ and “high position”

15 October 2026 · 6 min read

Turn over a blank tape from the eighties or nineties and you'll find a page of jargon: “IEC Type II”, “high position”, “70 µs”, “MOL +5 dB”. Reading a blank tape's J-card is easier than it looks. The type tells your deck how to set itself up, the C-number is the running time, and the spec figures let you compare tapes: higher MOL and SOL mean the tape can take more level before it distorts, and a lower noise figure means less hiss. Here's every line, in order.

The words on the front

You'll see	It means
C-60, C-90	Total minutes, both sides together: a C-90 is 45 minutes a side. Our guide to tape lengths has the full list.
Type I, IEC I, normal position, normal bias	Ordinary iron-oxide (ferric) tape. Plays back at 120 µs.
Type II, IEC II, high position, high bias, CrO₂	Chrome tape, or a cobalt tape that behaves like chrome. Needs high bias and plays back at 70 µs.
Type IV, IEC IV, metal position	Metal tape. Needs very high bias and a deck that can record metal. Plays back at 70 µs.
Ferric, microferric, cobalt, chrome, metal	What the magnetic coating is made of. Microferric is a finer, quieter Type I; most later Type II tapes are cobalt rather than true chrome.
120 µs, 70 µs, “3180 + 70 µs”	The playback EQ: how much the deck turns the treble down. The 3180 µs half of the pair is a bass setting that's the same for every type.

“Position” means the setting on a deck's tape selector. Early decks had a switch marked something like Normal, CrO₂ and Metal, so “high position” or “CrO₂ position” on a tape that contained no chrome at all just meant “set the switch to chrome”. Our guide to tape types explains what bias and EQ actually do.

How a deck reads the shell

The back edge of a cassette, seen from above. Every tape has a record-protect tab at each end. Type II adds a notch beside each tab, and metal adds another pair in the middle. Decks with automatic tape selection feel for them.

The international standard for cassettes made these detection notches compulsory in 1979. They're a quick way to identify a tape with no J-card. One exception: Type III (ferrichrome) tapes had no notches, so a deck reads them as Type I.

The spec table, line by line

Better tapes printed a table of measurements on the J-card or a leaflet inside. As an example, here are the published figures for a popular Type II tape, the TDK SA-90:

Line	Example	What it tells you
MOL (315 Hz)	+5.0 dB	Maximum output level: how loud a mid-range tone can be recorded before distortion reaches 3%. Higher means more room for loud, punchy music.
SOL (10 kHz)	−6.5 dB	Saturation output level: the most treble the tape will take before it stops getting louder. Closer to 0 means cymbals, synths and vocals stay crisp when you record hot. Sometimes printed as “MOL 10 kHz”.
Sensitivity	+0.5 dB at 315 Hz, +0.7 dB at 10 kHz	Output compared with the official reference tape for its type. Close to 0 means it matches how most decks were set up; a higher treble figure means a slightly brighter sound.
Bias noise	−60.5 dB	The hiss with nothing recorded, measured without Dolby. More negative is quieter.
Print-through	51 dB	How well a loud passage is kept from copying itself faintly onto the next layer of tape as a pre-echo. Higher is better, and it gets worse as tape gets thinner.
Coercivity	680 Oe (54 kA/m)	How hard the coating is to magnetise, which decides how much bias it needs. Roughly 380 Oe for Type I, 490–700 for Type II and about 1,100 for metal.
Remanence (retentivity)	1,750 G (175 mT)	How much magnetism the coating holds on to. More gives a stronger signal off the tape.
Thickness and length	12.5 µm, 135 m	Thinner tape fits more minutes into the shell but is more fragile.

You may also see dynamic range or S/N (signal-to-noise): the gap between the loudest clean level and the hiss. For hi-fi listening you want at least 60–65 dB.

“0 dB” isn't silence

Every level on the card is measured against a reference: usually the IEC level of 250 nWb/m, or the slightly lower Dolby level of 200 nWb/m. Makers didn't all use the same one or the same test deck, so a +6 from one brand and a +5 from another may not mean what they seem. Compare tapes from the same maker, or use magazine tests that measured tapes side by side.

What the numbers mean in practice

Chrome's advantage is quiet and treble, not level. A good Type I often has a higher MOL than a good Type II, but the Type II has less hiss and holds high notes better.
Metal is best at almost everything, with an MOL several dB above the others, but only on a deck that can record it.
Choose the type first, then the grade. The right type for the deck (and for the player it's going to) matters far more than a decibel either way. For a mixtape, a good Type I is the safe choice.
Sensitivity matters on a basic deck. A tape whose figures sit near 0 dB will sound right on a deck with no bias adjustment. Decks with a bias control or automatic calibration can fine-tune for anything.

The rest of the card

The index card. The inside of a blank-tape J-card was ruled for you to write on: a title, the tracklist, columns for the tape counter, and often boxes for the date, the source and noise reduction (see our Dolby guide).
Shell features. Precision shells, slip sheets, felt pressure pads and extra guide rollers were all about steadier running and less wobble. A shell held together with screws is also easy to open if the tape ever needs fixing (see our guide to looking after cassettes).
Leader. The clear or coloured tape at each end can't record; some makers used it to wipe the heads as it passed. Wind past it before you start recording.

Make your J-card say it

Several jcard.studio looks borrow this language. Speed Stripes says Type I · Normal position, Chrome Type II carries Type II · High position · 70µs EQ with a spec grid of length and minutes per side, Studio Black prints a bias and EQ table, and Metal Tape is labelled Type IV. Pick the one that matches the tape in the case.

Chrome Type II · open it →Studio Black · open it →

Chrome Type II and Studio Black, rendered by the designer. Click either to open it.

Making a tape? Design a J-card that fits the case.

Try the Studio Black look →