Glossary

Short	Name	Description
ALC	Automatic Level Control	This device adjusts the signal level that goes onto the tape during recording to prevent overloading it and causing distortion. As well as making the recorder easier to use, it saves the manufacturer having to fit a level indicator and control, both of which are bulky items. Miniature recorders such as the WM-R707 and simple low cost models, like the TC-12 use ALC, though it is not considered suitable for professional recorders, for example the WM-D6C, as it tends to "flatten" the dynamic range of music.
AMS	Automatic Music Sensor / Automatic Music Search	This is an arrangement fitted to some Walkman cassette players, such as the WM-EX618, and all Discman compact disc players which allows music tracks to be skipped through automatically. Cassette players use the gaps between the tracks to recognise where each track starts and finishes, and in all but the most sophisticated models can only repeat the current track or skip to the next one. Compact disc players use the digital information on the disc to find the tracks and can skip to any one instantly.
AR	Auto Reverse	This is a mechanical refinement of cassette player design that allows the machine to play both sides of the tape without the listener having to turn it over. In a compact machine like a Walkman, this is done using a special four-track head. Auto reverse greatly increases to complexity of a cassette player so it is usually found only on more expensive models, such as the WM-7. However, the inclusion of auto reverse does lead to some compromises having to be made in the design of the rest of the machine and precludes really accurate adjustment to the deck, so it is not found on serious professional machines such as the TC-D5, WM-D6 or WM-DC2.
ARO	Anti-Rolling	This term has no specific meaning, but describes a tape mechanism that includes measures to reduce the speed changes that can occur when the machine is moved or carried. Sony Walkmans tend to use counter-rotating flywheels for this purpose, or rely on disc-drive (dd) mechanism to prevent speed changes.
ATS	Automatic Tape Selector	Automatically detects the tape types. No need to manually select.
AVLS	Auto Volume Limiter System	This restricts the maximum sound level that the listener hears through the headphones. It was introduced to counter the claims that personal stereos could damage the listener's hearing if played too loudly for extended periods. AVLS is a limiter, and retards the volume only if the signal level is excessive. It first appeared on the WM-3000, which was intended for children. Later on it became common across the range, in models such as the WM-EX110.
BL Skip	Blank Skip	A feature of some Walkmans that makes the mechanism automatically fast forward past blank sections of tape. This feature is an extension of AMS, and is only included on a few well specified models, for example the WM-EX618.
Cue	Cue/Review	A cassette mechanism that allows fast forward or rewind to be temporarily engaged during playback so the sound can be heard at a much higher speed and at a reduced volume. This is useful for finding a particular passage in a speech programme, and it often found on Walkmans whose mechanical parts were initially designed for use in dictating machines, for example the TPS-L2.
DB NR	Dolby Noise Reduction System	Dolby noise reduction is a proprietary electronic circuit that is used under license. Its function is to suppress the characteristic background hiss present in all tape recordings. It is a two-part process, recordings have to be "encoded" by the recorder and "decoded" by the player. Many better Walkman models, such as the WM-DD2 feature Dolby "B" type noise reduction, it is not fitted to the more basic ones as the parts and the license are both quite expensive. Later, an updated and incompatible system, Dolby "C" was introduced. This was not popular and only appeared on a few models, for example the WM-DC2 and the WM-D6C. The weakness of both systems is that the degree of decoding required is indicated only by the signal strength of the recording. To work properly, this requires that the recorder and player are of identical, standardised performance and kept closely in adjustment. This proved difficult to achieve for mass-produced items like Walkmans and the system does not always improve the overall sound quality of a tape. Often a dull and indistinct sound results if the compatibility is not perfect.
DBB	Dynamic Bass Boost	See Mega Bass for Sony bass expansion; Philips also carried the same name for their bass expansion feature.
DD	Disc Drive	For Sony units, this stands not for "direct drive" but "disc drive"; Panasonic produced 3 true "direct drive" units. By the adoption of this special mechanism the wow and flutter performance of a cassette mechanism is dramatically improved, as is its immunity to movement and vibration. These improvements are particularly noticeable in small machines which can only accommodate lightweight, small diameter flywheels if conventional designs are used. A well designed and maintained DD Walkman can give speed stability performance that is difficult to distinguish audibly from CD or LP. A full description of the DD mechanism can be found on the TC-D5 page.
DOL	Dynamic Optimum Loudness	SONY developed the DOL system and integrated it on some of their top-level HI-FI products on 1986 (amplifiers and equalizers) and decided to include for the first time on a walkman, so they can compensate the typical poor bass response on portable players. The DOL system was the first attempt and after it many came, like the famous Mega Bass, and almost every brand on earth copied the idea under different names: DSL, Super Bass, Extra Bass, Bass boost...
EX DBB	Extended DBB
GEq	Graphic Equaliser	A system of multiple tone controls which each operate on a separate frequency band. The controls are always of the sliding type, and are arranged so that when set the sliders form a pattern that represents the frequency response characteristic of the system. This was a very popular device during the 1980’s and was initially offered for the Walkman user as an add-on unit. Later models offered built-in graphic equalisers, for example the WM-60.
HL	Hot Line	This function allows a person to talk to a Walkman listener without disrupting the playback of to tape. A microphone in the cassette player is switched in by pressing the hot line button and the sound from this is mixed in with the music on the tape, which is faded down at the same time. The microphone signal is not recorded on the tape. The technical term for this is "foldback monitoring". Only a few Walkman models included this feature, the TPS-L2, WM-3 and WM-R2. In practice, it turned out to be a complex gimmick of little practical use.
LC	Logic Controls (Feather-Touch)	Tape transport controls that instead of acting on the mechanical parts directly are electronic switches that instruct a logic circuit, which then operates the motors and solenoids which power the cassette mechanism. This is a complex arrangement, but necessary if complex functions such as AMS or Blank Skip are to be implemented, or if remote control is needed. The first Walkman with logic controls was the WM-7. All Discman compact disc players have logic controls.
MB	Mega Bass	A loudness system that increased the bass sound that a Walkman could provide through small headphones. It worked completely electronically, and adjusted itself depending on the content of the music and the volume control setting. Confusingly, Sony used the same term to describe a similar system in their portable radio cassette models that worked using an extra "sub woofer" loudspeaker.
OTR	One Touch Recording	A recording mechanism that can be started by operating one control only, rather than two in combination (e.g. Record and Play). This arrangement makes it easier and quicker to start a recording, but increases the chances of erasing and existing recording by mistake. The WM-R707 offers one touch recording.
PLL	Phase Locked Loop	A highly stable electronic circuit that can be used in radios to give accurate, drift-free tuning. Though it is not necessarily confined to radios with digital frequency readouts (like the SRF-M32), it has become synonymous with this type of set and is often used to refer simply to a radio with a digital tuning system.
TPS	Tape Program Sensor	(Panasonic) See AMS.