Manufacturers of bulk tape provided extremely detailed technical descriptions of their product, with numerous charts and dozens of numeric parameters. From the end user viewpoint, the most important electromagnetic properties of the tape are:
* Maximum output levels, usually specified in dB relative to the nominal zero reference level of  or the Dolby level of . Often incorrectly called recording levels, these are always expressed in terms of the tapes output', thus taking its sensitivity out of the equation. Performance at low and middle, and at treble frequencies was traditionally characterized by two related but different parameters:
**Maximum output level (MOL) is relevant at low and middle frequencies. It is usually specified at 315Hz (MOL) or 400Hz (MOL), and its value marks the point when the third harmonic coefficient reaches 3%. Further magnetization of the tape is technically possible, but at the cost of unacceptable compression and distortion. For all types of tape, MOL reaches a maximum in the 125800Hz area, while dropping off below  and above . The maximum output of Type I tape at  is 35dB lower than MOL, while in Type IV tapes it is 67dB lower. As a result, ferric tapes handle bass-heavy music with apparent ease compared to expensive metal tapes. Double-layer Type III (IEC III, ferrichrome or ferrochrome) tape formulations were supposed to allow bass frequencies to be recorded deeper into the ferric layer, while keeping the high frequencies in the upper chromium oxide layer.
** At treble frequencies the playback head cannot reliably reproduce harmonics of the recorded signal. This makes distortion measurements impossible; instead of MOL, high-frequency performance is characterized by saturation output level (SOL), usually specified at  (SOL). Once the tape reaches saturation point, any further increase in recording flux actually decreases output to below SOL.
* Noise level, usually understood as bias noise (hiss) of a tape recorded with zero input signal, replayed without noise reduction, A-weighted and referred to the same level as MOL and SOL. The difference between bias noise and the noise of virgin tape is an indicator of tape uniformity. Another important but rarely quantified type of noise is modulation noise, which appears only in the presence of a recorded signal, and which cannot be reduced by Dolby or dbx noise reduction systems.
* Dynamic range, or signal-to-noise ratio, was usually understood as the ratio between MOL and A-weighted bias noise level. High fidelity audio requires a dynamic range of at least 6065dB; the best cassettes tapes reached this threshold in the 1980s, at least partially eliminating the need for the use of noise reduction systems. Dynamic range is the most important property of the tape. The higher the dynamic range of music, the more demanding it is of tape quality; alternatively, heavily compressed music sources can do well even with basic, inexpensive tapes.
* Sensitivity of the tape, referred to that of an IEC reference tape and expressed in dB, was usually measured at  and .
* Stability of playback in time. Low-quality or damaged cassette tape is notoriously prone to signal dropouts, which are absolutely unacceptable in high fidelity audio. For high quality tapes, playback stability is sometimes lumped together with modulation noise and wow and flutter into an integral smoothness parameter.
Frequency range, per se, is usually unimportant. At low recording levels (−20 dB referred to nominal level) all quality tapes can reliably reproduce frequencies from  to , which is sufficient for high fidelity audio. However, at high recording levels the treble output is further limited by saturation. At the Dolby recording level the upper frequency limit shrinks to a value between  for a typical chromium dioxide tape, and  for metal tapes; for chromium dioxide tapes, this is partially offset by lower hiss levels. In practice, the extent of the high-level frequency range is not as important as the smoothness of the midrange and treble frequency response.