Playback Only Dynamic Noise Reduction Systems: Better Than Dolby Noise Reduction?

Are playback only cassette tape noise reduction systems like DNR offer better subjective performance than Dolby’s noise reduction systems?

By: Ringo Bones

Playback only noise reduction systems for use in cassette tape playback and reducing hiss when listening to FM radio broadcasts became widely available during the early 1980s. One of the most popular of these was the one based on the LM1894 IC used on what is referred to as a dynamic noise reducer or DNR. DNR units based on these types of ICs were praised for providing better subjective noise reduction results – sound quality wise – when compared to the then ubiquitous Dolby B noise reduction system used in entry level hi-fi cassette tape decks. But first here’s a discussion on how the DNR works.

According to its National semiconductor datasheet, the LM1894 is a 14-pin dual inline package stereo noise reduction IC for use with audio playback systems. This dynamic noise reduction – or DNR – system is non-complementary, meaning it does not require encoded source material. A noise reduction circuit using this IC is compatible with virtually all prerecorded tapes and FM broadcasts. Psychoacoustic masking and an adaptive bandwidth scheme allow the LM1894 IC based DNR to achieve 10dB of noise reduction. A DNR circuit based on the LM1894 IC can save circuit board space and cost because of the few additional passive components required. Described as a non complementary and single-ended noise reduction system that is compatible with all prerecorded tapes and FM broadcasts, has a 10dB CCIR / ARM weighed effective noise reduction, has a 4.5 volts to 18 volts power supply range that’s compatible for installation in automotive applications and a 1 volt RMS input overload.

The dynamic noise reduction system is a low pass filter that has a variable bandwidth of 1,000 Hz to 30,000 Hz, depending on music spectrum. The DNR system operates on three principles of psychoacoustics. The first of which is that white noise can mask pure tones. The total noise energy required to mask a pure tone must equal the energy of the tone itself. Within certain limits, the wider the bandwidth of the masking noise about the tone, the lower the noise amplitude need be. As long as the total energy of the noise is equal to or greater than the energy of the tone, the tone will be inaudible. This principle may be turned around; when music is present, it is capable of masking the noise in the same bandwidth. Next, the ear cannot detect distortion lasting less than 1 millisecond. On a transient basis, if distortion occurs that is less than 1 millisecond in duration, the ear acts as an integrator and is unable to detect it. Because of this, signals of sufficient energy to mask the noise allows the LM1894 DNR IC to open its operating bandwidth to 90-percent of its value in less than 1milliseconds. Reducing the bandwidth to within 10-percent of its minimum value is done in about 60-milliseconds: long enough to allow the ambience of the music to pass through, but not so long as to allow the noise floor to become audible. And lastly, reducing the audio bandwidth reduces the audibility of the noise. Audibility of noise is dependent on the noise spectrum or how the noise energy is distributed with frequency. Depending on the tape and the recorder equalization, tape noise spectrum may be slightly rolled off with frequency. Depending on the tape and the recorder equalization, tape noise spectrum may be slightly rolled off with frequency on a per octave basis. The ear’s sensitivity, on the other hand, greatly increases between 2,000 Hz and 10,000 Hz. Noise in this region is extremely audible. The DNR system’s low pass filters makes the noise less audible by filtering steady-state hiss in this frequency. The low frequency spectrum of the music will not appreciably open the DNR’s bandwidth, thus hiss in the 2,000 Hz to 10,000 Hz part of the audio spectrum is not heard.

The LM1894 IC is often used in conjunction with the 18-pin dual inline package LM3915 LED bar-graph driver array driver IC as a bandwidth indicator. The resulting set-up cosmetically resembles the dbx 563X Hiss Reducer that was sold during the late 1980s and early 1990s. Sadly, by around 1986, the LM1894 DNR IC was becoming hard to find in most DIY electronic stores – especially if you’ll going to buy just one IC instead of “a minimum quantity of 1,000 chips” as often advertized in popular electronics magazines at the time. While building my own DNR unit back in 1987, I was forced to replicate the transconductance amplifier portion of the LM1894 IC using discrete FETs.

In use, playback only single-ended DNR type noise reduction systems provide subjectively better sound quality results in comparison to Dolby noise reduction systems like Dolby B and Dolby C because most DNRs operate their cutoff frequency in the in the 1,000 Hz to 2,000 Hz part of the audio system, while Dolby B operates in the 500 Hz zone, thus making DNRs sound less “dull” than an over-aggressive Dolby B. But in actual use, Dolby encoded prerecorded tapes – in either Dolby B or Dolby C encoding – tends to perform well in a typical DNR unit in comparison to tapes recorded without any Dolby noise reduction because a Dolby encoded cassette tape has a substantial treble boost than ones recorded without Dolby. 

Headphones: Less Than Ideal Way To Listen To Cassette Tapes?

Even though it was deemed an indispensible component when the Sony Walkman became king back in the 1980s, are headphones, until now, has always been a less than ideal way to listen to cassette tapes?

By: Ringo Bones

Dubbed by conservatives as the most antisocial way to listen to music back when Sony’s Walkman was new, the shortcomings of the ubiquitous headphones has recently been brought back into the spotlight after the shortcomings of a flagship Apple product – i.e. the Apple AirPods wireless headphones and their Mainland Chinese made knockoffs – as early users complained of excessive background hiss, not to mention early users old enough to remember 1980s era cassette tapes saying that the hiss levels are worse than that of tape-to-tape dubbing a copy of a copy of a prerecorded cassette tape album. But are headphones really the weakest link of all the sound producing transducers in our high fidelity audio hobby – especially when it comes to listening to prerecorded cassette tape albums?

Despite its shortcomings, audio enthusiasts old enough to have taken sound quality seriously back in the 1980s had surprisingly managed to make due of listening to music via headphones. Weird between-the-ears stereo soundstage when listening to plain vanilla 2-channel stereo cassette recordings and producing more background hiss in comparison to conventional loudspeakers notwithstanding. But let us explore more on the headphone’s hiss issue given that, especially when listening to prerecorded cassette tape albums as your primary music source, is already inherently hissy in the first place.

Hiss is more noticeable through headphones than speakers for several reasons. Since headphones lie closer to the ears of the listener in comparison to loudspeakers, any hiss that the headphones’ produce is readily transferred to the eardrums. Headphones are more sensitive than loudspeakers – i.e. headphone sensitivity are typically measured in decibels per milliwatt as opposed to decibels per watt when measuring loudspeaker sensitivity – so headphones are more likely to pick-up the faint residual hiss produced by your audio rig, like that in the preamplifier stage and / or the Dolby noise reduction stage. And headphone models that isolate your ears from outside sounds can also prevent such sounds from masking hiss, denying the user from using Mother Nature’s naturally generated dither noise.

Unconventional Cassette Tape Deck Alignment Hacks For Extreme Cassette Sounds?

Even though proper alignment of tape heads are a necessity for playback compatibility when playing a tape from one deck to another but is it possible that a bit “unconventional” alignment results in a superior sound quality from cassette?

By: Ringo Bones

For those old enough to remember how “unconventional” cassette tape head azimuth alignment tweaks back in the late 1970s to the 1990s managed to transform their humble walkman or a car stereo like the famed Pioneer KP-500 to rival that of a full-sized open-reel tape deck or an audiophile CD player using various everyday items like strategically placed match-books, paper clips and even bobby pins knows how rewarding this bit of DIY can be. Though it can be taken to an extreme when it causes cassette tape skewing problems and an “eaten tape”, within a certain envelope, these tweaks can offer rewards in terms of much improved sound quality from prerecorded cassette tapes.

Unconventional cassette tape head azimuth alignment head tweaks gained notoriety back in the late 1970s due to neophytes and jumpy electronic tinkerers upon hearing a tape deck cough, they immediately get hold of a screw driver and give the azimuth alignment screw of the tape head a couple of tweaks. The first thing to remember most of all is that the heads need adjustment only when they are being replaced in the case of worn-out tape heads. To find out if the tape heads do need adjustment – or for those buying a used cassette tape deck at a keen price at a garage sale – check if the tape head’s wear pattern is rectangular. If it is trapezoidal or varies much from head to head, they need to be adjusted. On the other hand, never adjust heads that have actually been worn out unless you want some tape travel and skewing problems. Problems about worn-out cassette tape heads are solved by complete head replacement.

But the good – or bad – news is that within a certain “latitude”, some minimal tape head azimuth tweaks via strategically placed match-books, paper clips and bobby pins – especially in entry level walkmans – can result in treble clarity that can make your humble walkman, car stereo or boom-box rival that of an open-reel tape deck and audiophile grade CD players in the 2,000 to 5,000 US dollar price point. If you have old Hair Metal prerecorded tapes from the 1980s, sometimes, the result can be as eerie as akin to being less than 20 feet away from a well-struck crash cymbal. I remember now that this is how we did cassette tape high frequency clarification tweaks before “affordable” decks by Yamaha and NAD with the “Play Trim” feature became widely available during the 1990s.

Can You Use Dolby B Noise Reduction On Dolby C and Dolby S Encoded Cassette Tapes?

Even though your tapes won’t be damaged if you do this, are there any benefits of using Dolby B noise reduction on Dolby C and Dolby S encoded cassette tape audio recordings?

By: Ringo Bones

Fortunately, doing so will not result in a damaged cassette tape or tape deck, but the practice gained popularity back in the late 1980s and early 1990s – or whenever time Dolby C and Dolby S encoded prerecorded cassette tapes became widely available. I mean I even heard of one audiophile back in 1993 praising the sound quality of Gen. H. Norman Schwarzkopf’s spoken word album after playing a Dolby S encoded cassette copy of on a car stereo that’s only equipped with a Dolby B noise reduction system. But first, here’s a brief review of the Dolby C and Dolby S noise reduction systems.

Dolby B reduces tape noise at frequencies starting at 500-Hz and achieves a noise reduction of 8 to 10 dB while Dolby C starts to work at 150-Hz and above and achieves a noise reduction of 18 to 20 dB, But Dolby S is a simplified domestic use version of the Dolby SR – a professional signal processing scheme and not just a mere noise reduction strategy. Dolby S consists of a number of circuits operating together to reduce tape noise right across the 20-Hz to 20K-Hz audio band, not just in the high frequencies where Dolby B and Dolby C operate – and Dolby S will do this with minimum possible audible intrusion.

But given that doing so – fortunately will not damage both tape and deck – why is it then that this scheme results in an inexplicably improved subjective sound quality? Well, it could be the resulting “treble lift” due to the different playback curve of Dolby B compared to Dolby C and Dolby S noise reduction systems and the resulting treble lift compensated for the inherently noisy automotive environment. And the different playback curves of the various Dolby noise reduction systems also resulted in lifting the mid-range portion of the audio spectrum that resulted in a vacuum-tube like warmth in tonality of a solid state car tape deck. Which, unfortunately, resulted in car stereos – especially those models made by Alpine – target number one for car break ins. Using Dolby B noise reduction on Dolby C and Dolby S encoded cassettes also benefitted Walkman / portable cassette tape players during the late 1980s and early 1990s because most affordable Walkman models at the time are only Dolby B noise reduction capable - all of this proving Philip's claims that the Dolby C and Dolby S noise reduction systems are "backwards compatible". 

What Are The Most Important Specifications of a Cassette Tape Deck?

Whether a fist time buyer or a seasoned cassette tape archivist – what are the most important specifications of a cassette tape deck?

By: Ringo Bones

Given that the “lowly” cassette was the only egalitarian music medium for the budding audiophile back in the mid 1980s, it is easy to say that most of us have his or her own view when it comes to what specifications make a great cassette tape deck. But if you ask me, what I will rank from the most to least important goes as: (1) frequency response, (2) wow and flutter, (3) signal-to-noise ratio, (4) speed accuracy and (5) distortion – although some audiophiles may rank distortion higher as the most important specification.

Frequency response that’s flat- i.e. within ±3dB - and extends from 30-Hz to 18,000-Hz – could be considered impressive. But you should pay attention on how flat the response is, a frequency response specification of ±6dB is not impressive. However, if the specifications were ±3dB and applied to a range of 30-Hz to 16,000-Hz would be considered acceptable. Better still would be a much flatter range of ±2dB over such a frequency range. A high frequency range that extends to 19,000-Hz instead of just 16,000-Hz will not make an important difference to most listeners – especially “older” audiophiles. 

The wow and flutter should measure no higher than 0.05% peak. Although, people who are more sensitive than others when it comes to wow and flutter might require a tape deck with better specification in this department– i.e. 0.025% or lower.

The signal-to-noise ratio should be at least 75dB or better when using Dolby C noise reduction. And the deck should offer better S/N ratio results when a more advanced noise reduction system is used – like Dolby S.

Speed accuracy that that will deviate no more than 0.5% from correct speed. While some engineers consider such deviation in pitch is inaudible to most people, vinyl LPs are mastered on a device whose pitch deviation is under 0.2%.

Low distortion is of vital importance, especially if you exclusively play recorded acoustic instruments because it is much easier to hear distortion creeping in with a violin recording – than with a Gibson Les Paul played through an overdriven Marshall stack.

Why Cassette Tapes Aren’t Magnetically Shielded?

Given their propensity to go dull whenever they are accidentally placed near magnetic objects – even magnetic screwdrivers - why aren’t cassette tapes provided with inherent magnetic shielding?

By: Ringo Bones

Unlike your Barclay-Crocker prerecorded Open Reel tapes that came in mu-metal cans as standard, prerecorded cassette tapes back in the 1980s and even well into the 21^st Century doesn’t come with protection against erasure when accidentally placed against a strong magnet like refrigerator magnets and electric guitar pickups and electric bass guitar pickups. And if you Google search cassette tapes that are magnetically shielded, you are directed into Google’s lists of invented patents stating that the tiny nickel plated piece of steel behind the pressure pad functions as a “magnetic shield” for the cassette tape. Given that this concern was largely ignored by the leading cassette tape manufacturers during the format’s lifetime, is it even possible to magnetically shield cassette tapes against erasure and loss of high frequencies when accidentally placed closed to magnetic screwdrivers, fridge magnets, and electric guitar and electric bass guitar pickups?

Back in 1979, the world’s leading cassette tape manufacturer TDK released their MA-R series of cassettes and they were the top of the line of the company’s Type –IV metal particle cassettes. The tape formulation used is based on TDK’s patented Finavix particle. It’s very heavy and its metal shell construction – later revealed to be an aluminum-zinc alloy – has the potential to be made with an actual mu-metal alloy capable of actually provide magnetic shielding for the cassette housing instead of just a vibration reduction measure. Sadly, given that these were top of the line in the TDK’s range of cassettes, they were also very expensive. From the 1980s through to the 1990s, TDK’s MA-R series of metal particle cassette often carry a retail price of around a dollar and a half to two dollars less than a price of a compact disc - which for all intents and purposes just too high a price to pay for a blank cassette tape. This largely explains why I totally abandoned prerecorded cassette tapes in the mid 1990s when the “relatively affordable” Marantz CD-63 Ken Ishiwata Signature model entered the market. 

Avilyn Magnetic Particles: The Greatest advancement In Cassette Tape Development?

Though now largely forgotten, did the Avilyn magnetic particles represent the absolute zenith of cassette tape advancement?

By: Ringo Bones

This substance has now virtually become an “alien technology” for those born way after the heyday of the cassette tape. But back then, this represented the value-for-money in cassette tape technology terms when it comes to sound quality. Besides the more expensive metal particle tapes, cassette tapes that use Avilyn magnetic particles are probably the closest yet to sounding like professional open-reel tapes. Stranger still, Avilyn magnetic particle technology has its origins way before cassette tapes become a runaway commercial success in the 1980s.

Developed as a high coercive magnetic particle developed for sound and video recording back in 1974, Avilyn is an acicular magnetic iron oxide on whose surface certain cobalt compounds have been adsorbed. The coercive force of the particles is determined by the amount of cobalt and other preparing conditions, and is controllable between 450 and 800 Oe (Oersteds). The particles display much improved thermal stability with respect to remanence and coercive force. The new video tape having a coercive force of 550 Oe is compatible with chromium dioxide video tape in recording characteristic according to measurements on a conventional video tape recorder. The head wear rate of the new Avilyn tape is about one-fifth that of chromium dioxide tape and is almost the same as for conventional iron oxide tape. Tape demagnetization is not as serious as is in the case of cobalt-doped gamma ferric oxide tapes.

During the 1980s, Avilyn was mostly used in TDK’s high-bias Type-II cassette tapes and VHS video tapes. TDK also produces Avilyn open-reel tapes for professional studio recording use at the time when 16-bit digital audio recording technology was still in its infancy. Sadly, during the early part of the 21sr Century as the prices of recordable compact discs and associated equipment came tumbling down and availability increased, everyone’s love affair with the cassette tape slowly waned.

GoldStar Blanks Cassette Tapes: The Best Value for Money Blank Cassette Tapes of the 1990s?

Even though the company has since renamed itself did GoldStar managed to manufacture the best value-for-money blank cassette tapes back in the 1990s?

By: Ringo Bones  

Now known as LG, the South Korea based GoldStar managed to build one of the best value-for-money consumer electronic and data storage media products back in the 1990s. Even my 14-inch GoldStar color TV model CN-14A146 with serial number 60514212 that was bought back in July 1995 still works to this very day. And did you also know that GoldStar managed to manufacture value-for-money blank cassette tapes whose performance were comparable to that of up-market TDK and Maxell blank cassette tapes during the 1990s? 

Even though TDK Type-I ferric blank cassette tapes were the most widely available here in South East Asia during the 1990s, many audiophiles preferred GoldStar’s series of blank cassette tapes because they are on average cost one-fifth as much as equivalent TDKs. TDK’s D series of Type-I normal ferric cassette tapes normally sell for around 1 US dollars each back in the 1990s, GoldStar’s HR series of Type-I normal ferric cassette tapes on average sell for around 20 US cents each – only voices grade cassette tapes destined for phone answering machines were cheaper – but Goldstar’s HR series of cassette tapes like their GoldStar HR60 (60-minute) and GoldStar HR90 (90-minute) cassettes managed performance that’s comparable to TDK’s higher spec normal Type-I ferric tapes like their TDK AD and AR series of  Type-I cassette tapes. 

And during the mid 1990s, GoldStar blank tapes managed to make your cassette tape equipped car stereo and Walkmans sound like the famed Marantz CD 63 SE Ken Ishiwata signature model if you placed a GoldStar HR series of normal blank cassette tapes on an audiophile quality cassette tape deck – these start at around 150 US dollars each brand new back in the mid 1990s – and record from a good value for money CD player like the famed Marantz CD 63 SE KI Signature. And GoldStar also manufactured value-for-money Type-IV metal particle cassette tape like their GoldStar MTX60 and MTX90 series of cassette tapes during the 1990s and they too cost one-fifth as much as comparable TDK metal tapes.      

Tips For Recording A Loud Hair Metal / Heavy Metal Bands Onto Cassette Tape?

Given that cassette tape, as a recording medium, has inherent limitations in the low and high frequency extremes, would you still be able to record good loud hair metal tunes on it?

By: Ringo Bones 

Whether from a live band or from a “realistic sounding” open-reel analog master tape, the lowly compact cassette really has inherent limitations when recording very low and very high frequencies at very loud levels. And yet during the heyday of hair metal – between 1980 to 1992 – recording studio mavens managed to make a significant number of recordings that managed to sound very good on the lowly cassette tape which during the time, was still the dominant recording medium and it wasn’t until the mid 1990s that CD players that can be described as both affordable and good sounding entered the market. Maybe it’s just for nostalgia, but here are a few tips on how to record a loud hair metal band onto cassette tape and make them sound relatively pristine. 

Of all the cassette tape recording tips, the one that’s frequently overlooked is that audio cassette tapes can have a hard time handling very high and very low frequencies. In the low end, the lowest bass notes like the open E-string form a bass guitar – at around 40 Hz – can cause distortion if the level is too high. In the high frequencies, sibilance or “sss-sounds” can cause tape distortion via high frequency saturation so using a de-esser helps keep things under control during mastering onto cassette especially if the open reel master tape was recorded at 30 inches per second with gobs of very loud and pristine high frequencies. If you are already saturating cassette tapes from excessive high frequencies, boosting your high frequencies to create a ” brilliant timbre” cassette recording will only cause more trouble. 

One tricked employed by 1980s era heavy metal bands in recording onto cassettes that resulted in a “brilliant” sound without resulting in distorted high frequencies is by mixing in more presence in the upper midrange / lower high-frequency range – from 2,000 Hz to 6,000 Hz – to mask the tape hiss of low-cost Type-I ferric cassettes. Giving more space between the microphone and acoustic guitars and cymbals will definitely help – especially back in 1989 where acoustic electric Ovation guitars with built in equalizers that were then in vogue when hair metal era heavy metal bands record power ballads often produce enough high frequencies to saturate Type-I ferric cassette tapes with ease.  

When recording your master tape onto cassette, use a multi-band peak limiter with a built-in pre-emphasis before limiting, like the Behringer Combinator or Aphex Dominator or a high frequency limiter. The resulting cassette will be more open-sounding without sounding unduly dull in comparison to its open-reel master tape. Using a good high-pass filter to roll off very low frequencies definitely helps because cassette tapes tend to compress when recording signals below 50 Hz or so. Even up-market Nakamichi cassette tape decks produce “horrendous” harmonic distortion readings below 50 Hz. 

Use a device that adds brilliance only to low-level signals. That is what Dolby B does in its encoding stage. The higher the input level, the less high-frequency boost Dolby B gives. The widely used cassette tape recording “plug-in” called the Aphex Aural Exciter with its “Big Bottom” mode and similar devices work similarly by adding low levels of high-frequency harmonic distortion. This is tricky because you generally want to push the cassette tape as loud as possible just to the cusp of distortion and saturation, but if you already have distortion in your mix – especially in the open-reel master tape – there may be a compounding effect. And if you want to avoid your drum-kit – especially the kick drum – from sounding like a 1980s era synth-samples, practice restraint when it comes to boosting low frequency signals below 50 Hz.  

High Bias Type II Cassette Tapes: The Most Cost Effective Upgrade form Normal Cassette Tapes?

Costing on average twice that of Normal Type I cassette tapes are High Bias Type II cassette tapes the most cost effective upgrade for the budget conscious audiophile?

By: Ringo Bones 

During the 1980s – and in fact well into the 1990s and the first decade of the year 2000 – audiophiles who still use cassette tapes in compiling their own “mix tapes” for personal listening via Walkman or car stereo will probably gravitate towards TDK’s Super Avilyn cobalt-doped series of high bias Type II cassette tapes despite that on average these costs twice as much as Normal or Type I cassette tapes. But is the improvement in sound quality really worth the cost? 

In my actual experience on the matter, CD players were still a relative rarity in the 1990s and no CD potable – then and now – even approaches the sound quality capability of the famed Marantz CD 63 SE Ken Ishiwata Signature. But inexplicably, if you are lucky enough to own or have access to a good sounding CD player and an excellent audiophile tape deck, like a Marantz CD 63 SE connected to those Technics “Thin Film Tape Head” series of cassette decks, recording your CDs onto a TDK Super Avilyn blank cassette even without resorting to speed doubling could make your still functional 1980s era Sony Walkman sounds as good as a Marantz CD 63 CD player. 

To me at least, my primary raison d’être for using high bias tapes over normal tapes is that not only that high bias tapes like TDK SA can record better high frequencies in comparison to normal cassette tapes but also of their low noise or tape hiss. Walkmans and car stereos are usually equipped with Type II High Bias 70 μ second / Type I 120 μ second switch. Switching the setting to Type II 70 μ second usually results in a noise reduction that’s better than Dolby B without the dulling effect of low cost cassette playback equipment with a not optimally set Dolby B noise reduction system . And I bet others' preference of other high bias tapes than the TDK SA over normal Type I tapes may be largely due to tape hiss issues.

Commonly Available Test Cassette Tapes, Anyone?

Even though Mobile Fidelity Sound Labs’ Geo Tape is the one often mentioned, are there more widely available test cassette tapes out there?

By: Ringo Bones 

Believe it or not, even well into the 1990s – and probably even until this day – there’s still no agreed for the level at which the 0VU peak record level is set on high fidelity cassette tape decks. During the 1990s, the 200nWb (nano Weber) Dolby flux was most commonly used for quality budget decks, but lower down the price scale on budget designs with inferior tape heads that would overload at a much lower level, 0VU is set -3dB below Dolby. Some top line models, like Nakamichi, have their 0VU set high up at IEC 0dB flux of 250nWb which many audiophiles and engineers, then and now, think is most sensible. But is there a reliable way to “calibrate” the cassette tape decks you currently own regardless of quality even if you don’t have access to a sophisticated signal generator and an oscilloscope? 

The British made Harrison Test Cassette available from Canford Audio which retailed for around £20 back in the mid 1990s is one of the most widely available and often turns up in garage sales and weekend swap meets. This has Dolby level plus other tests that are useful in aligning cassette tape decks. While the “Cadillac” of test cassette tapes are those BASF IEC test tapes, especially those that are IEC Primary Reference Standard which back in the mid 1990s costs £69.20 each. But it is a very reliable way to establish IEC 0dB using the “Level Control 315Hz Code-XB” track and given that it is a premium quality cassette test tape, it can establish IEC reference level to a degree of certainty manufacturers cannot question. 

After having reliably establish IEC 0dB, you can now record to around +4dB above it on musical peaks on metal tape and around +2dB on ferrics and chromes. And don’t forget to add 2dB to these figures if you set the 0dB of your cassette tape deck at 200nWb Dolby flux. But the most effective test you can perform after aligning your cassette tape deck is on how effectively it can record music tracks.