Editing Dbx (noise reduction) (section)

===Tape hiss===
Magnetic tape consists of microscopic particles that can be magnetically charged to record signals. The size of the particles and the speed of the tape transport defines the maximum frequency that the media can record. For [[high fidelity]] recordings, [[reel-to-reel audio tape recording]] typically works at tape speeds of 15 or 7.5 inches-per-second (38 or 19&nbsp;cm/s), but this requires a lot of tape for a given amount of recording. Lower fidelity recordings can be made at 3.75 or even 1.875 ips, which allows more recording time on a given tape, but at the cost of adding more high-frequency noise.<ref name="Nave_2001_4"/>

The [[cassette tape]] was designed for convenience, not audio quality, and ran at 1.875 ips (4.75&nbsp;cm/s) to maximize recording time in the relatively small (compared to open-reel) tapes. This resulted in significant [[tape hiss]]. Combined with their limited width, which limits the [[dynamic range]] of the signals, the hiss tended to overwhelm any high frequencies in the signal, especially low-volume ones.<ref name="Nave_2001_4"/>

During the 1970s, several new types of magnetic recording films were introduced, notably "chrome" and "metal", that used smaller particles and thereby pushed the tape hiss to much higher frequencies. During the same period, noise reduction systems like dbx and Dolby attempted to do the same using conventional media and actively addressing the tape noise through electronics.<ref name="Nave_2001_4"/>