Remembering Ray Dolby – Father of Tape Noise Reduction

Though his iconic invention made him a very wealthy man, could the world of hi-fi and music be very different today if Ray Dolby hasn’t bequeathed his invention to the public for almost nothi

By: Ringo Bones   

Sadly, Ray Dolby passed away Friday, September 13, 2013 aged 80. Forever remembered after the iconic noise reduction system that bears his name, the music and hi-fi world would probably not exist as we know it today without his inventive solution in tackling the perennial problem of magnetic recording tape hiss.

Ever since the US Armed Forces introduced working samples of World War II era German analog open-reel tape recordings and their associated tape recording and playback equipment near the end of the 1940s in various trade expos, many American audio engineers suddenly got an epiphany that tape hiss or noise is not going to be an easy problem to solve. This is so because tape noise results mainly from the lack of homogeneity of the magnetic coating. Even with existing technology – then and now – the ferrous particles can never be distributed absolutely uniformly throughout the coating and the resulting aggregations of these particles create discrete magnetic fields which – during replay – manifests itself as noise e.m.f. or tape hiss at the playback head and thus amplified along with the desired audio signal. 

Luckily, a then young electronics engineer named Ray Dolby managed to formulate – i.e. engineered - a very cost effective solution that became a noise reduction system that is named after him. Thanks to Ray Dolby, the lowly cassette tape that was primarily created by Philips as an office dictation medium was raised to high fidelity status and became a very cost effective analog tape based music recording medium since the latter half of the 1970s and even displacing vinyl LP in popularity as a domestic hi-fi playback medium during the 1980s. In a sense Ray Dolby’s iconic noise reduction system virtually raised every cheap magnetic tape recording based media into audiophile status.   

In 1967, Henry Kloss heard about Ray Dolby’s noise reduction system – i.e. the Dolby A which was intended for professional studio recording noise reduction applications during the Rock N’ Roll era. It was Kloss who pushed for a consumer version of the Dolby A noise reduction system which is now known as the Dolby B, which Kloss originally saw as a boon to home/domestic open-reel tape users – and made the Philips compact cassette – which Philips originally intended as an office dictation medium – into a runaway commercial hi-fi success that virtually out-competed the better sounding vinyl LP near the end of the 1970s.

Thanks to his financial success, Ray Dolby also paved the way for various inventions and inventors to make domestic high fidelity a much more affordable hobby. Using the same Peter Scheiber patents of the old quadraphonic sound systems that expired with barely a whimper back in 1975, Dolby Laboratories managed to create Dolby Pro Logic – a surround sound system that made possible those relatively affordable surround sound capable home cinemas during the early 1980s that also made low-cost mediums like the VHS or Betamax video cassette tapes – and even cassette tapes – capable of life-like surround sound reproduction when used with a designated Dolby Pro Logic decoding box. 

Unbeknown to most of us, Ray Dolby first cut his teeth in the field of radio astronomy. In fact, his Dolby Noise Reduction System came from his earlier work in trying to extract very weak cosmic radio signals from background radiation noise mainly caused by our very own radio telecommunications traffic. 

Dolby S Noise Reduction System: Savior Of The Cassette Tape?

In spite of its “heroic” audio engineering specs, why hasn’t the Dolby S noise reduction system been able to save the cassette tape from eventual commercial extinction?

By: Ringo Bones 

Introduced back in 1989 with the hopes to extend the cassette tape’s “commercial lifetime” well into the 21^st Century despite of the onslaught of the digital media competition, Dolby S was introduced to the hi-fi masses primarily to make commercially produced mass-market prerecorded cassette tapes sound as good – if not virtually indistinguishable from the 16-Bit 44.edbook spec CDs. Sadly, according to the major consumer electronic entertainment firms, tape-based recording and playback systems – like the cassette tape – we are told, is just isn’t acceptable anymore during the early to mid 1990s because it has an old-fashioned image. Not to mention the proliferation of CDs (both brand new and reissue albums – even hard-to-find rarities) only a dollar or two more expensive than their prerecorded music cassette tape album versions sold in music stores and the proliferation of “affordable” (as in between 350 to 500 US dollars each) CD players from Marantz, NAD and Rotel which now sound as smooth as their entry-level vinyl LP playback system counterparts. Despite its inability to save the “commercially doomed” and aging cassette tape format, what makes Dolby S so special in comparison to its other Dolby cassette tape noise reduction system predecessors? 

Dolby B and Dolby C are cassette tape hiss reduction processes which, in essence, boost the signal to be recorded in order to keep it much louder than the tape hiss. On playback, the boost is reversed, drastically reducing the volume of the hiss in the process. A complication arises because the boosted signal must not be allowed to peak so high that the tape cannot accommodate the signal, and it is solutions to this problem that made every Dolby noise reduction system developed so far such an outstanding success. The Dolby B circuit reduces noise above approximately 500 Hz and achieves about 8 to 10 dB of noise reduction while Dolby C is effective above approximately 150 Hz and achieves about 18 to 20 dB of improvement in the signal-to-noise ratio. Although Dolby C noise reduction employs more treble boost than Dolby B noise reduction, Dolby C includes a special recording characteristic to avoid saturating the cassette tape at extremely high audio frequencies approaching 20 KHz. But his doesn’t mean that it’s perfect, or that Dolby B or Dolby C tackles all of the problems associated with recording unto cassette tape. This is where Dolby S steps in.

Dolby S is the simplified for consumer use / domestic use version of the Dolby SR – a professional signal processing scheme, not just a mere noise reduction strategy. It consists of a number of circuits operating together to reduce tape hiss right across the audio frequency band of 20-Hz to 20-KHz – not just the high frequencies where Dolby B and Dolby C operate – with the minimum possible audible intrusion. Several different measures are taken to ensure that noise reduction is supplied in such a way that the background hiss – including the microphone and first-stage preamplifier hiss, not just tape hiss – can’t be heard to vary, which is the problem with Dolby C in particular, especially with piano and transient-rich music. 

Techniques employed including varying the bandwidth of the signal compressors as the music changes using three separate stages of signal processing to cover the entire 20-Hz to 20-KHz audio frequency band, and using weighed networks and filters that modify the action of the processors where the system is likely to be audible. If you like Dolby S analyzes the nature of the signal to be recorded and responds to it intelligently. In use, Dolby S achieves an improvement of 23 to 25 dB of signal-to-noise ratio.  

A secondary property or benefit if you will, of commercially produced Dolby S encoded cassette tape recordings is that in the absence of a Dolby S decoder equipped cassette tape playback deck, as in older cassette tape decks, they will operate satisfactorily with a Dolby B processor at a cost of some mild compression, which can actually be beneficial. This is especially noticeable in-car cassette tape playback systems where the ambient noise levels can swamp the quieter musical passages. Given such “heroic” abilities, why didn’t the Dolby S noise reduction system manage to save the cassette tape from being crowded out by the 16-Bit CD and even the strongly resurgent vinyl LP competition during the mid to late 1990s? 

Being fortunate enough to have a hands-on review of the two most popular “almost affordable” Dolby S equipped cassette tapes being sold back in 1994 – the Sony TC-K611S which sold for 460 US dollars at the time and the Kenwood KX-7050S which sold for 560 US dollars. Thanks to our very friendly local hi-fi dealer who at the time used the two Dolby S equipped cassette tape decks in a more or less in an almost permanent demo basis, given that the two were the only high-ticket items practically flying out of the shelves back then. Sadly, Dolby S doesn’t make up for a lack of talent elsewhere. I mean the rather audible – from a musician / music lover’s ears’ perspective – wow and flutter of the 100 US dollar cheaper Sony TC-K611S cassette tape deck made a rather unacceptably “wow and fluttery” rendition of the prerecorded cassette of Tori Amos’ Little Earthquakes album, while the rendition of the Kenwood KX-7050S was less musically convincing than a similarly priced Nakamichi cassette deck which our friendly hi-fi shop owner owns and often uses as a reference for reviewing cassette tape decks – and no, the Nakamichi doesn’t have Dolby S. Compared to the similarly priced Nakamichi, the Kenwood had a less than musically convincing performance – especially in the mid-band. Although both the Dolby S equipped Sony and Kenwood cassette tape decks delivered a hiss-free performance. 

The resulting hands-on review only serves to reinforce my preconception of consumer electronic products I since harbored since my childhood during the 1970s that mechanical sophistication can be replaced by electronics, bringing enormous cost savings in the process. These days – or back in the post Operation Desert Storm days of 1992, electronics come cheap, but mechanical parts don’t. Cassette tape decks are a complex amalgam of mechanics and electronics. The Japanese being undisputed masters of the former managed to manufacture the best and relatively affordable transport mechanisms and record / playback heads during the cassette tape’s heyday in the 1980s. For example, Nakamichi makes great recording and playback heads for cassette tape decks, but you can bet they are a far more costly way of obtaining an increased dynamic range than the Dolby S modules in the cassette tape deck’s signal path. Even though it failed to prevent the commercial extinction of the cassette tape, at least Dolby S may have extended its commercial lifetime of the cassette tape up to until 2008. 

Surround Sound From Cassette Tapes?

Even though they were relatively widely available during the late 1980s and early 1990s, why didn’t the surround sound encoded cassette tapes became more popular than they should?

By: Ringo Bones 

As someone who grew up during the heyday of “physical music media”, music lovers back then gauged the popularity of a newfangled music recording gimmick by how soon it is applied to the hard rock and heavy metal music genre. And though it is not as popular as it should have, finding cassette tapes that are Dolby Pro-Logic surround sound capable of hard rock and heavy metal live concerts during the late 1980s and early 1990s is enough for one old enough to ask why are these types of cassette tapes never became standard issue? But first, let’s discuss a brief history of surround sound. 

 When the concept of surround sound – as in quadraphonic sound – was let loose to consumers during the early 1970s, the best surround sound systems during quadraphonic’s heyday were discrete quadraphonic on four-track open reel tapes. This was by far the best delivery system for the quadraphonic sound system but these tapes were just too expensive for the average audiophiles of the day. Even though quadraphonic sound systems – i.e. 1970s era surround sound – expired with barely a whimper in 1975, it was a concept that was introduced rather too late for a more consumer friendly priced quadraphonic sound system, a matrix decoder type surround sound with logic steering that became the basis of the Dolby Pro-Logic surround sound system that eventually reintroduced the concept of surround sound for the home around the middle of the 1980s. 

Based on the same Peter Scheiber patents as the old quad systems which Dolby Laboratories added their own proprietary improvements, the Dolby Pro-Logic system managed to rekindle the consumers’ interest in of surround sound in the home during the mid 1980s because its surround sound encoding system can be seamlessly introduced – more or less – into two-track stereophonic audio already widely used in cassette tapes and the VHS and Betamax videocassettes of the time while still allowing the very same Dolby pro-logic encoded cassette tapes and videocassettes to be played on ordinary two-channel stereo systems with no loss of sound quality. The great thing about the Dolby Pro-Logic surround sound system is that it can impart relatively accurate surround sound steering data even on bandwidth restricted recording and playback media like the Philips compact cassette. 

All the analog based encode / decode surround sound systems - like Dolby Pro Logic – use a sum-and-difference matrixing system to shoehorn front and rear and the center channels into the main stereo pair. Front center, of course, was left-signal / right-signal mix, because L+R is what produces a phantom center in stereo. The rear channel was recorded out-of-phase in the front left and right channels, so that the process that recovers the signal will cancel out the other. Strictly speaking, the surround signal lagged the left stereo channel by 90 degrees of phase and led the right channel by 90 degrees, so that it was anti-phase between the stereo channels but only a symmetrical 90 degrees out-of-phase with either stereo channel.      

  

Unfortunately, when using the scheme as is, channel separation between adjacent channels is a lousy 3 dB, so a technique called logic steering was ultimately used to monitor the stereo signals, then “decide” which is the dominant channel at a given instant, and subtract the channel’s signal from the ones adjacent to it. For instance, when the left front signal is dominant, its signal is cancelled from left back and center front. When the surround channel is dominant, its signal is subtracted from the left and right fronts. Even with logic steering, there’s usually some leakage of the front left and right signals into the rear, so a small time delay is put in the surround channel to harness the ears’ tendency to localize sounds in the direction they are first heard from. 

Despite the good results obtained from Dolby Pro Logic encoded cassettes to recreate a believable surround-sound at the home even with a budget Dolby Pro Logic equipped receiver, most analog matrix encoded surround sound were eventually superseded by full-digital surround sound systems like Dolby Digital AC-3 surround sound and DTS starting in the early 1990s. As good as Dolby Pro Logic was – even in cassette form – its surround sound channels just don’t have the 20 KHz or greater bandwidth of full digital surround sound systems like Dolby Digital AC-3 and DTS.  

Was the 8-Track Better Than The Cassette Tape?

Even though both formats seem to be pitted against each other during much of the 1970s and the first half of the 1980s, was the 8-Track better than the cassette tape? 

By: Ringo Bones 

Upon first inspection, it is way more mechanically complicated than the cassette tape, but with its intended application in car stereos, 8-Track does have the ergonomic advantage over Philips’ cassette tape since 8-Track plays in a continuous loop – i.e. once the last song of the album or 8-Track cartridge ends, it goes back to the first track / song. But there are those who still swear that as an analog tape format, the 8-Track has a better subjective sound quality than cassette – and if you are a serious audio enthusiast – if you’ll ever hear a well-set up 8-Track deck, you would swear that it is way better, sound quality wise, than cassette tape too. But first, here’s a brief history on the 8-Track tape. 

William Powel Lear a.k.a. Bill Lear was the oft credited inventor of the 8-Track tape, though other people – like Earl “Madman” Muntz - were instrumental of its culmination as a commercially successful product; Though most of the younger generation often tend to associate Bill Lear with the Lear Jet. The   8-Track cartridge or 8-Track tape is a magnetic tape based sound recording and playback format. It was very popular in the U.S. and other countries with a large U.S. military presence from the mid 1960s to the early 1980s but was relatively unknown in most European countries. 8-Track tapes were used as a carrier for quadraphonic sound during the start of the 1970s by simply reallocating the tracks but later reverted to its original two-channel stereo applications once the quadraphonic fever died with barely a whimper in 1975.

The endless loop tape cartridge was first designed back in 1952 by Bernard Cousino around a single reel carrying a continuous loop of standard ¼ inch plastic oxide coated recording tape running at 3 ¾ inches per second (9.5 cm / sec). Program starts and stops were signaled by a one-inch long metal foil that activates the track-change sensor. Bill Lear had tried to create an endless loop wire recorder in the 1940s but gave up in 1946, even though endless-loop 8mm film cartridges were already in use for him to copy from. Lear would then be inspired by Earl Muntz’s four-track design in the early 1960s. 

As a relatively more complicated mechanical system compared to the Philips’ cassette tape, the 8-Track tapes’ shortcomings were mostly mechanical related like higher that average wow and flutter measurements due to constantly changing load presented by the sliding tape pack. There’s also a tendency of the 8-Track to jam as the tape got dirty as the lubricant wore away and dries up as the tape is exposed in the rather hostile elevated temperatures of the automotive environment. The flattening of the pinch roller over time when an 8-Track cartridge was left plugged in causing increased wow and flutter and the last one was the inability to attain and maintain tape head alignment due to the movable head design. Though this list of shortcomings was mostly confined in 8-Track’s automotive use, its domestic applications – especially with dedicated recording and playback heads – can sometimes produce subjective sound quality results far better than that obtained from cassettes. 

 When recording unto 8-Tracks via a dedicated 8-Track recording deck like the Pioneer RH-65 8-Track Player/Recorder or the Pioneer H-R100 8-Track Player Recorder using either CDs, vinyl LPs, DVD-Audio and Super Audio CDs, the results were far better than any cassette deck on a rung lower than that of the Nakamichi. Even if the specifications show that 8-Track tapes only measure a bit better than 55dB signal-to-noise ratio even with Dolby B noise reduction on, 8-Tracks produce a much more open midrange compared to cassette tapes. His is probably due to much more tape of the 8-Track being run faster across a recording head to capture more resolution of the recorded event. And since the 8-Track tape’s being run at twice that of cassette’s 1 7/8 inches per second, the apparent wow and flutter problems are apparently only audible on more demanding Classical piano recordings than on everyday rock and pop. 

 

dbx: The Forgotten Cassette Tape Noise Reduction System?

Though it was touted during the cassette tape’s heyday as the noise reduction system that can make tapes as silent as digital recordings, has dbx now been relegated to the technological dustbin of history?

By: Ringo Bones

As a budding hi-fi enthusiast during the latter half of the 1980s and a semi-pro studio musician during the late 1980s and the early 1990s, it seems – from my own perspective – that the dbx noise reduction system is more popular in the pro-audio field than in home hi-fi. And even though in this day and age of barely-legal and barely-audiophile sounding digital music downloads, has dbx been largely forgotten?

Even though the dbx name had only been familiar to hard-core audiophiles who want to extract the last ounce of performance from cassette during the 1980s, dbx – the company – is much more than a mere “cassette tape noise reduction company”. The company, I think, has two main business addresses – their consumer gear division can be contacted at dbx, Incorporated, 71 Chapel Street, Newton, MA 02195. While their pro audio division can be contacted at (well, at least according to the business card they gave me back in 1990) at dbx Professional Products, A division of AKG Acoustics, Inc. 1525 Alvarado Street, San Leandro, California 94577, USA.

Product wise, dbx is a family of noise reduction systems developed by the company of the same name that was used not only for cassette tape noise reduction for the home, but also for professional applications in the “modern” recording studio and for noise reduction of sound reinforcement systems used for  live stadium concert applications. The original dbx Type I and Type II systems were based on so-called “linear decibel companding” – that is the audio signal to be recorded onto a recording medium has its dynamic range compressed and then its dynamic range is expanded upon playback to not only make it sound as close to the natural recorded event as possible, but also to transcend the dynamic range limitations of most existing analog recording mediums at the time. The dbx companding-expanding system was invented by David E. Blackmer of dbx, Inc. in 1971.

In practice, the dbx noise reduction system encodes the audio signal to be recorded (or transmitted) with 12-dB preemphasis (boosting the high frequency part of the audio spectrum) prior to compression. The purpose of which is to further boost the high frequency signal content above the hiss level. An additional preemphasis network is placed in the control voltage (detector) signal path. The extra boost further reduces the compressor gain, keeping recorded high-frequency program content below the saturation point of the tape. This ensures that high-level input signals will not saturate the tape.

There are actually two types of dbx noise-reduction systems, Type I is intended for high speed – 15 inches per second tape speed or greater – tape recording and playback operation and for use with any other wide-band audio transmission system. For slower tape speeds and other restricted bandwidth media – like cassette tapes and vinyl LPs – the dbx Type II noise-reduction system is used. The main difference between Type I and Type II dbx noise-reduction systems can be found in the level detection circuits.

At around 1981, if one wants to record and plays back his or her prerecorded dbx tapes or wants to dbx encode his or her DIY cassette tape recordings, he or she can use an external stand-alone dbx noise reduction processor like the dbx Recording Technology Series Model 224 which was advertised in Stereo Review magazine’s January 1981 edition with a MSRP of about 300 US dollars – which is already a lot of money in 1981, and I have the good fortune to use this myself near the end of the 1980s. At the time, the dbx Recording Technology Series Model 224 was touted as the then “cheapest” way to achieve recordings having a signal-to-noise ratio of 90dB – akin to then existing digital recordings – for home use / making DIY recordings. In cassette tape use, the dbx noise-reduction / dbx NR system operates throughout the audio range and does not require matching record and playback levels. Thus, there is no tracking problem that can affect treble response.

However, it has been noted that playback response at the frequency extremes, particularly at the treble end, tends to be not as good with dbx as with Dolby B and C NR – i.e. Dolby B and C NR tend to sound more natural on acoustic Classical and Jazz music compared to dbx. The dbx system achieves about a 30dB reduction in noise while Dolby B NR only achieves about 10dB while Dolby C NR 20dB. So why did dbx, despite its excellent specs, got “crowded out” in the market place by lesser-performing Dolby noise-reduction systems?

The general lack of acceptance of the dbx noise-reduction system in the consumer electronic marketplace during the go-go 1980s is that all dbx encoded recordings sound unacceptable – i.e. has an over-compressed dynamic range or no variation between loud and soft musical passages – when played on playback equipment without dbx encoding despite the very excellent improvement in sound quality. The first generation of dbx stand alone noise-reduction processors intended to be connected to your existing playback equipment – like your cassette tape deck and turntable for vinyl LP playback – were kind of prohibitively expensive for most hi-fi enthusiasts back in 1981. And despite allowing you to play your cassette tapes and vinyl LPs with the same lack of noise and hiss as that of the late 1970s era professional digital recording system – the JVC DAS-90 system - mainly used in digitally recording and mastering mainly Classical music performances around 1980 – dbx died barely a whimper around 1982. Even dbx encoded vinyl LPs released during 1973 to 1982 were capable of having a signal-to-noise ratio of 120 dB, by the way, Redbook spec 16-bit 44.1-KHz sampled CDs were only capable of around 98dB signal-to-noise ratio - and the JVC DAS-90 digital recording system probably has a lower signal-to-noise ratio than this - even with hiss free full digital recordings.

In my own experience, the dbx noise-reduction system seems more suited to recording and listening pop/rock music without the residual hiss from the cassette tape medium. Even though the cut-price dbx decoding of my own Technics RS-T55RP cassette tape deck, a cassette tape recording of Night Ranger’s Sister Christian was played back with a dynamic range punch reminiscent that of a live stadium rock concert, though as the strongly stuck drums died down, the softer piano parts of this particular Night Ranger song tend to pump and wheeze the cassette tape’s hiss – the oft criticized aspect of dbx artifacts known as breathing / noise modulation. And it seems that even pro audio gear made by dbx primarily aimed for live concert stage noise reduction – i.e. the dbx 563X Hiss Reducer – which around 1990 was primarily used to reduce the hiss of guitar effects stomp boxes using the rather noisy LM 741 op amp IC as the active gain element – also works as an excellent external cassette tape noise reduction / hiss reduction box too.