Record Bias Self-Adjusting Cassette Tape Decks: Technological Tour De Force?

Given that this late 1970s ingenious innovation to further optimize the recording performance of the “lowly” compact cassette, did record bias self-adjusting cassette tape decks truly qualify as a technological tour de force? 

By: Ringo Bones 

Every serious cassette tape recordists during the late 1970s may don’t have yet the “technical vocabulary” to the problems besetting them arising from the Philips compact cassette performance and manufacturing limitations, it seems that every advances in technology aimed at extracting every bit of performance of the lowly compact cassette seems to be a fast track to nowhere. Even with the 4 types of broadly standardized cassette tape types, namely the: Type-I or Normal Bias 120 microsecond entry-level tape, Type-II or High-Bias 70-microsecond Chrome Position cassette tape, Type-III or Ferrichrome cassette tape purposely built for the “acoustically noisy” car environment and the Type-IV or Metal Position 70-microsecond metal particle cassette tape, which at the time, represented the pinnacle of cassette tape technology for those wanting open-reel tape performance in a compact cassette tape package. So “technological utopia” for the lowly cassette tape has finally been reached, right? 

When recording tape – whether open-reel or compact cassette types – is improved in any significant way – even if the change is something as ostensibly physical as a smoother coating surface, with the magnetic particles themselves left unchanged – the tape now behaves differently with real-world tape decks as an electromagnetic entity. Generally, the tape now requires – or at least would benefit from – a different level of recording-bias current, followed by the obligatory touch-up of the tape deck’s default record equalization curve. Unfortunately for the typical everyday cassette tape recording enthusiasts, these are adjustments that require good – and usually expensive – instruments and a certain amount of technical expertise to accomplish; Not to mention that these adjustments are also very time consuming to perform. 

Cassette tape recording enthusiasts back in the late 1970s more often than not experienced first hand the “rude awakening” of buying a handful of cassette tapes from their local retailer for the sole purpose of finding out which brand suit them best only to find out later that all of them require somewhat different levels of fine tuning of the recording bias and equalization of the cassette tape deck they currently own. Optimizing your cassette tape deck for each one so that you can evaluate noise levels and other important performance criteria for cassette tape recording will more often than not prove to be a project of Herculean proportions. Then there’s also the problem of cassette tape manufacturers’ batch variations. For the sake of example, TDK’s cassette tape production for June is not likely to be identical to the production batch made previously in March. Very serious cassette tape recordists at the time often buy in quantity from a single batch and resign themselves to readjusting their cassette tape decks when their supply stash of cassette tapes ran out and a new batch must be investigated. This is hardly a formula for progress thus the raison d’être for the self-adjusting record-bias cassette tape deck was born. 

The user-selectable tape type accommodation abilities of record bias self-adjusting cassette tape decks and the ease it can perform these “arduous” tasks has been widely hailed at the time as the solution for this very dilemma. Back then, they look as if they are the next step forward in the technological evolution of the few innovative cassette tape decks already incorporating two-tone oscillators that enables the user to achieve a reasonably flat frequency response with virtually any cassette tape out on the market when it comes to do-it-yourself field recording of music and other “real” acoustic events or just simply dubbing the recorded contents of other prerecorded cassette tapes being played from a separate dedicated deck. 

The most advanced of the first generation of these record bias self-adjusting cassette tape decks were equipped with 4-bit analog to digital converters to accurately sample the MOL of the test-tones being recorded on the cassette tape under evaluation and a 3-bit floating point microprocessor system to process the data in order to perform the necessary adjustments to dial in just the right amount of record bias to enable the tape deck to automatically “fine tune” the maximum MOL while minimizing total harmonic distortion and flat frequency response that the cassette tape under evaluation is truly capable of. 

Even though such analog-to-digital conversion and processing power seems lowly by today’s standards, it enabled those early generations of self-adjusting cassette tape decks to perform 96 steps of bias level adjustments and 16 steps of EQ and sensitivity adjustments – with 0.5 dB of resolution. With a good tape, these early decks were said to be able to maintain a recording frequency response tolerance – or flatness – of plus and minus 0.5 dB over much of the audio frequency range. This sort of performance will only do wonders to these tape decks’ ability to portray a fairly accurate imaging and sound-staging of the acoustic event in the space it is trying to record. 

Thanks to this record bias self-adjusting cassette tape decks, there will be no more tape jungle to flounder through for the serious cassette tape recordist. He or she will be able to buy an armload of different manufacturers’ cassette tapes, take them home, and in the course of a civilized, low-pressure evening decide for himself or herself what his or her brand is going to be, without the worry that a non-compatible cassette tape deck is making a good tape look (or sound) bad. By the same token, cassette tape manufacturers will finally be able to concentrate their full efforts on making a genuinely better cassette tape. It will not be just a somewhat better tape that has been compromised a little because it must match the factory-set performance and adjustment profile of earlier generations of cassette tape decks already in the hands of potential customers. 

     

Bias Level: The Be-All-End-All of Cassette Tape Recording?

Even though the standards of the high-frequency pre-magnetization or a.c. bias became more or less sacrosanct around World War II, does it truly represent the most important factor in the serious cassette tape recordists’ life? 

By: Ringo Bones 

The newer hi-fi generation weaned on better CD players and the recent vinyl LP revival may be too young to remember, but there was a time when recording bias level – i.e. the alternating current used in electromagnetic preconditioning of tape-based analog audio tape recording was the be-all-end-all of the serious cassette tape recordists’ life. Around the time when B-List actor Ronald Reagan just got nominated by the US Republican Party to run as the next president of the United States and the Ayatollah Khomeini was too busy enjoying the spoils of his “Islamic Revolution”, some upmarket cassette tape decks started sporting 4-bit microprocessors that automatically optimize blank cassette tape and cassette tape deck co-performance beyond the Normal Bias / Type-I, High Bias / Type-II, Ferrichrome / Type-III, Metal/Type-IV selector switch of the typical cassette tape deck at the time. And many enthusiasts at the time who press cassette tape for high fidelity music recording use eventually found out that even a little too much applied recording bias level can cause erasure of high frequencies – the very spectrum that tends to give life to recorded music. Given that tape recording bias level for all intents and purposes could be considered at the time as the most important factor in the serious cassette tape audio recording, what is it and what makes it so special? 

Around World War II, the manufacturer of the AEG/Magnetophon R22 magnetic tape recorder for recording and broadcasting more or less made the standard for setting bias levels for all tape-based analog audio recording. Tape bias alternating current frequency is usually set at least five times the highest audio frequency to be reproduced in order to minimize the audible interaction between the pre-magnetization a.c. bias and the harmonics of the highest audio frequencies – a sort of “Nyquist Criterion” for analog audio tape-based recording. Thus if you seek a tape recording frequency response that goes up to 20,000 Hz, the bias should be at least 100,000 Hz. And some upmarket tape decks manufactured between the late 1980s and mid 1990s have their record bias frequency set as high as 125,000 Hz!  

During the cassette tape’s heyday, bias level has been the tricky consideration in the whole high fidelity music recording process, in large part because the optimum record bias level for a tape is largely a controversial issue. Depending on your criteria, you could choose a bias level – either manually or via your newfangled self-adjusting cassette tape deck’s built in 4-bit microprocessor – that: (1) maximizes the output MOL of the cassette tape at some reference frequency – usually 1,000 Hz; (2) minimizes third-harmonic distortion from your tape – for a test frequency of your choice, but often one in the vicinity of 1,000 Hz; (3) minimizes modulation noise; (4) minimizes intermodulation distortion in any of a number of two-tone tests; or (5) satisfies any of a number of “ideal” criteria for the relative useable output levels from the cassette tape at low and high frequencies. 

Play Trim: A High-End Cassette Tape Deck Necessity?

Introduced around the mid 1990s in upmarket high-end cassette tape decks, does the Play Trim facility qualifies as a high-end cassette deck necessity? 

By: Ringo Bones 

High-end cassette decks circa 1995 might see like an oxymoron to us audiophiles but it became a buzzword to audio product retailers and tenured hi-fi reviewers during the period. But does the 1990s era compact cassette innovations during the time managed to give the humble Philips compact cassette a few more years worth of reprieve from being phased out? 

In practice, the Play Trim facility in upmarket cassette tape decks was hailed by those who still use the compact cassette as their primary music recording and listening medium during the 1990s as a very useful facility to get the best – or was in most – from prerecorded music cassette tapes. Play Trim eliminated the associated dullness of record store bought prerecorded music cassette tapes by acting as a specialized treble control placed in front of the cassette deck’s built-in Dolby noise reduction system. 

To casual listeners, most Play Trim equipped cassette decks introduced in the 1990s allowed prerecorded music cassette tapes to sound well enough – in comparison to the compact disc during that period. And also, most Play Trim facilities offered plenty of adjustment to counter the inherent dullness – i.e. rolled off high frequencies – that afflicts many prerecorded music cassette tapes released by major music labels at the time, especially if the listener opts to switch the Dolby noise reduction on to reduce tape hiss. 

The Humble Philips Compact Cassette Tape: Past Prologue?

This “reluctant” music recording medium’s demise might have been a tad exaggerated, is the humble Philips’ compact cassette still alive and kicking? 

By: Ringo Bones 

Even though it seems to have vanished overnight in some parts of the world back in 2009, the internet is still abuzz with testimonials that the humble compact cassette is still used by revolutionary firebrands to spread their radial political messages in parts of the world yet to enjoy the benefits of Web 2.0. Not to mention independent record labels of the punk rock, death metal, black metal  genre who don't have their own vinyl pressing plants for making 7-inch 45-rpm singles. Given the reluctant music medium’s illustrious 50-year history, will Philips’ compact cassette ever “retire in dignity”? But first, an illustrious look back to the reluctant music recording medium that could. 

Back in 1963, the European arm of Philips launched the compact cassette. It was primarily introduced as a dictation medium for use in Philips office voice / dictation recording machines that were then licensed to be manufactured by Norelco. And there were very blatant signs that Philips never engineered the compact cassette to be a high fidelity music recording medium because of the inherent narrow track width and the slow tape speed of 1 and 7/8 inch per second (4.76 centimeters per second) making it prone to tape saturation. William Lear’s 8-Track tapes that runs twice as fast and has twice the track width easily bettered the cassette as a convenient consumer-based music recording medium and quarter-track open-reel tapes at the time offered even higher performance when run at seven and a half inches per second. 

But around 1967, there were some visionary high fidelity enthusiasts who placed it among themselves to make Philips’ humble compact cassette into a viable true high fidelity music recording medium. During that year, hi-fi manufacturing visionary Henry Kloss heard about Ray Dolby’s noise reduction system initially intended for professional – as in recording studio – applications. It was Kloss who pushed for a consumer version of the Dolby noise reduction system, which Kloss originally saw as a boon to open-reel tape users. Some months later, Henry Kloss linked the Philips compact cassette system with a previously unsuccessful DuPont product – chromium dioxide tape. Thanks to the magical midwifery at which Henry Kloss excels, these seemingly disparate inventions helped make the Philips compact cassette – originally introduced for office dictation recording purposes – into a high fidelity music storage medium that eventually went on to surpass the vinyl LP and even CD sales in 1989. 

Famous and established musicians from the 1960s also did their part in pushing the Philips compact cassette into a high fidelity music playback and storage medium. Near the end of 1967, The Rolling Stones’ guitarist Keith Richards used an early Philips Norelco cassette recorder originally marketed as an office dictation recording machine to record the now distinctive guitar parts of their iconic song Street Fighting Man. Thirty years later, the late Ted Hawkins’ 16 tracks from the McCabe’s show were originally recorded on standard cassette – and while they’ve been improved on the 1997 The Final Tour album via 1990s era HDCD processing, these tracks still exhibit limited dynamic range. 

And before us mere civilians were taught by Tim Berners-Lee on how to master the then US DoD’s DARPANET – now known as the internet – if a revolutionary firebrand wants his or her messages to go “viral”, recording your speeches on scores on cassette tapes was the only way to go. That is if the despotic government you intend to overthrow keep jamming your CB radio transmissions. The Iranian religious leader Ayatollah Khomeini used the cassette tape route to make his Islamic Revolution a runaway success while toppling the Shah of Iran back in 1980. And did you know 50 years before thumb drives / USB drives became de rigueur mass data storage devices, the lowly Philips compact cassette was once used to store chunks of computer data – even its operating system as was once shown in that James Bond movie called Diamonds Are Forever?