Editing Cassette deck (section)

==Noise reduction and fidelity==
[[File:Technics SCD 615 geschlossen.jpg|thumb|HiFi-Tapedeck by [[Technics (brand)|Technics]] with analog [[VU-meter]]s (1977)]]
A variety of [[Audio noise reduction|noise reduction]] and other schemes are used to increase fidelity, with [[Dolby B]] being almost universal for both prerecorded tapes and home recording. Dolby B was designed to address the high-frequency noise inherent in cassette tapes,  and along with improvements in tape formulation it helped the cassette win acceptances as a high-fidelity medium. At the same time, Dolby B provided acceptable performance when played back on decks that lacked Dolby circuitry, meaning there was little reason not to use it if it was available.

The main alternative to Dolby was the [[dbx (noise reduction)|dbx]] noise reduction system, which achieved a high [[signal-to-noise ratio]], but was essentially unlistenable when played back on decks that lacked the dbx decoding circuitry.

[[Philips]] developed an alternative noise reduction system known as [[Dynamic Noise Limiter]] (DNL) which did not require the tapes to be processed during recording; this was also the basis of the later [[Dynamic Noise Reduction|DNR]] noise reduction.<ref>[http://freespace.virgin.net/ljmayes.mal/comp/philips.htm Circuit and description of DNL] {{webarchive |url=https://web.archive.org/web/20081105073059/http://freespace.virgin.net/ljmayes.mal/comp/philips.htm |date=November 5, 2008 }} URL accessed August 25, 2006</ref>
[[File:JVC KD D10E v.jpg|thumb|JVC KD-D10E with Dolby B]]
Dolby later introduced [[Dolby C]] and [[Dolby S]] noise reduction, which achieved higher levels of noise reduction; Dolby C became common on high-fidelity decks, but Dolby S, released when cassette sales had begun to decline, never achieved widespread use. It was only licensed for use on higher end tape decks that included dual motors, triple heads, and other refinements.

[[Dolby HX Pro]] headroom extension provided better high-frequency response by adjusting the inaudible [[tape bias]] during the recording of strong high-frequency sounds, which had a bias effect of their own. Developed by [[Bang & Olufsen]], it did not require a decoder to play back. Since B&O held patent rights and required paying license fees, many other manufacturers refrained from using it too.

Other refinements to improve cassette performance included Tandberg's DYNEQ, Toshiba's {{Interlanguage link|adres|ja}} and Telefunken's [[High Com]], and on some high-end decks, automatic [[recording bias]], fine pitch adjustment and (sometimes) head azimuth adjustment such as the Tandberg TCD-330 and TCD-340A.
[[File:TDK MA-R90 Compact Audio Cassette.jpg|thumb|TDK MA-R90 cassette]]
By the late 1980s, thanks to such improvements in the electronics, the tape material and manufacturing techniques, as well as dramatic improvements to the precision of the cassette shell, [[tape head]]s and transport mechanics, sound fidelity on equipment from the top manufacturers far surpassed the levels originally expected of the medium. On suitable audio equipment, cassettes could produce a very pleasant listening experience. High-end cassette decks could achieve 15&nbsp;Hz-22&nbsp;kHz±3&nbsp;dB [[frequency response]] with [[Wow (recording)|wow]] and [[Flutter (electronics and communication)|flutter]] below 0.022%, and a [[signal-to-noise ratio]] of up to 61&nbsp;dB (for Type IV tape, without noise-reduction){{Citation needed|date=March 2012}} . With noise reduction typical signal-to-noise figures of 70-76&nbsp;dB with Dolby C, 80-86&nbsp;dB with Dolby S, and 85 - 90&nbsp;dB with dbx could be achieved. Many casual listeners could not tell the difference between compact cassette and [[compact disc]].

From the early 1980s, the fidelity of prerecorded cassettes began to improve dramatically. Whereas Dolby B was already in widespread use in the 1970s, prerecorded cassettes were duplicated onto rather poor quality tape stock at (often) high speed and did not compare in fidelity to high-grade LPs. However, systems such as [[XDR (audio)|XDR]], along with the adoption of higher-grade tape (such as chromium dioxide, but typically recorded in such a way as to play back at the normal 120 μs position), and the frequent use of Dolby HX Pro, meant that cassettes became a viable high-fidelity option, one that was more portable and required less maintenance than records. In addition, cover art, which had generally previously been restricted to a single image of the LP cover along with a minimum of text, began to be tailored to cassettes as well, with fold-out lyric sheets or librettos and fold-out sleeves becoming commonplace.

Some companies, such as [[Mobile Fidelity]], produced [[audiophile]] cassettes in the 1980s, which were recorded on high-grade tape and duplicated on premium equipment in real time from a digital master. Unlike audiophile LPs, which continue to attract a following, these became moot after the compact disc became widespread.

Almost all cassette decks have an [[MPX filter]] to improve the sound quality and the tracking of the noise reduction system when recording from an FM stereo broadcast. However, in many especially cheaper decks, this filter cannot be disabled, and because of that record/playback frequency response in those decks typically is limited to 16&nbsp;kHz. In other decks, the MPX filter can be switched off or on independently from the Dolby switch. On yet other decks, the filter is off by default, and an option to switch it on or off is only provided when Dolby is activated; this prevents the MPX filter from being used when it's not required.