Tape recording is one of the two means commonly available for storing a musical performance, and one of the three different program sources available to the consumer (the other two being disc and radio broadcast). It is unique in combining these two functions in one domestic package. The process consists of passing 'magnetic tape' across a record head that imposes a signal or coding of the programme upon the tape; this signal can be retrieved by passing the tape back across a replay head (sometimes the same head with the appropriate switching circuitry) where the code generates a much smaller electrical signal for amplification and replay.
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The tape itself consists of a flexible plastics backing on which is deposited a carefully controlled coating of special metal-oxide particles. The chemical makeup of these particles endows them with magnetic properties, and small magnetic fields can be generated within them.

In fact the tape coating consists of a myriad of these small magnetic fields, which are arranged haphazardly when no recording has been made. The recording and playback heads consist of coils wound on iron or other formers with a small gap across which the tape passes.

When a signal is fed into the coil it generates a magnetic field in the gap, which changes according to the signal being applied. If a tape is dragged past the gap, this changing magnetic field is 'printed' on the particles in the tape. When at a later date the tape is again dragged across the gap, a (much smaller) signal is generated in the coils which should be a replica of the original, and this can then be amplified.

So we have a system which can 'map' a signal onto a magnetic material, but this is only part of the way towards recording and playing back a music signal with any degree of fidelity.

In order to map the information accurately, the system should respond with equal sensitivity to all the frequencies to which the human ear can respond (at the very least, and some engineers would claim subsonic information is also important).

The system must also be able to respond accurately to changes in sound level, so that the loud stays loud, the soft soft and the crescendo crescends! In fact the human ear can hear frequencies between 20 Hz and 16 kHz (the abbreviation Hz meaning cycles per second which corresponds to the pitch of the sound).

One other essential function for a tape recorder is to erase the tape that is about to be recorded, and this is accomplished by passing the tape over an erase head before it reaches the record head.

This carries a signal that oscillates at a very high frequency with plenty of current and effectively jumbles up any previous magnetic code on the tape. A small proportion of this erase signal is fed to the record head and mixed with the signal being recorded to enable the tape to make a recording of reasonably low distortion.

This is known as the bias current, and while it is needed to reduce distortion, it also partly erases the high frequency signals, so considerable electronic boost or equalisation has to be applied by the deck amplifiers at high frequencies on both record and replay (see Technical Introduction).
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To make any decision about compatibility between the cassette deck and the rest of a hi-fi system it is of course necessary to know the relevant parameters of the amplifier or receiver, namely the tape input sensitivity and impedance and tape output level and impedance.

Sensitivities are normally quoted as a minimum while output levels tend to be quoted as a maximum, so the cassette deck should have a somewhat higher output than the amplifier's tape sensitivity, while the cassette deck's input should be slightly more sensitive (ie a lower figure) than the amplifier's tape output level.

As a rule of thumb, when using phono interconnections signals prefer to travel from a low to a high impedance. The German DIN standard is the opposite, so when using these sockets to interconnect, the signals will go from a very high to a substantially lower impedance.

It is frankly not possible to explain this adequately without getting the reader and writer tangled up in technical terminology, so it is best to leave the explanations to the Technical Introduction and hope that this is sufficient to satisfy the practical needs of the non-technical reader. The reviews also include details on the maximum acceptable input signal, known as the clipping point, which should not be exceeded by the amplifier source signal.

Most cassette decks and amplifiers contain both DIN and 'phono' sockets for interconnecting equipment. These employ somewhat different standards, and it is always advisable to use one or the other type exclusively, and avoid situations where a phono output is connected to a DIN input or vice-versa.

It is also a good general rule to use the input and output level controls on the cassette deck somewhere towards the middle of their operating ranges to avoid noise or clipping problems, so if there is a choice of input sensitivities, this may be the deciding factor.

If one is going to make a 'magnetic model' of a piece of music by passing the tape across a recording head, and then 'reconstitute' the music at a later date, it is obvious that the tape must be passed at exactly the same speed each time - an engineering impossibility.

What happens in practice is that small variations exist that distort the signal to some extent, and these are usually known as wow, flutter and drift.

A single note may thus suffer a slight change of pitch which can be detected as very long (drift) or short (wow) variations or 'blurring' (flutter). The situation is often made worse (though not necessarily more detectable) when increasingly complex music signals are used, and as anyone with a strong interest in music will appreciate, it is the easily lost subtleties that are the most important part of any performance.

Things are not made any easier by the inherent constraints of the cassette format, which was never originally conceived as a hi-fi medium of course. Superior results could probably be achieved if the tape itself could be isolated from the mechanical and physical limitations of its housing for record and replay (a feature of the commercially unsuccessful Elcaset system), but while some designers have shown considerable ingenuity in this respect, the actual mechanics of the tape itself still have a significant effect.

The cassette machine therefore has an extremely complex mechanical task to accomplish, which involves passing the tape across the heads with no speed variation or vibration while being subject to various frictional forces. The heads themselves provide one element of friction; the two reels of tape must be correctly tensioned when they are of both large and small diameters at the beginning and end of the tape, and this is usually accomplished using a frictional clutch system.
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To make matters worse, the hum fields and vibrations from the motors used must not be allowed to interfere with the position of the tape relative to the heads or cause undue heat either.
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'Three-head' decks, where the record and replay heads are separated so that the design of each can be better optimised and off-the-tape monitoring employed, have been criticised on the grounds that the increased complexity of the mechanical problems involved makes for more problems than the system's other advantages are worth.

These are merely the most obvious problems in maintaining the flow of the tape past the heads, whilst maintaining at the same time close and consistent contact between head and tape. Other mechanical considerations involve allowing the tape to be fast-wound at a reasonable speed and changing from one function to another without causing any damage or stretching the tape.

A further area of importance that is unfortunately rather beyond the scope of the report concerns the long term consistency and reliability of the transport mechanism, which can be quite difficult to maintain when dealing with such fine tolerances.

Indeed all the inherent mechanical problems of tape recording in general tend to be magnified in the cassette format, partly because of the fine tolerances involved and the dependance on mass-produced software mechanics, but also because the low overall tape speed used will show a greater percentage charge for the same actual fluctuation than would be detected at a higher speed.

Ergonomics, Features and FacilitiesOften these appear to be the only things that distinguish one cassette deck from another, and naturally they are largely a matter of individual taste.

One golden rule however remains - all features must be paid for! The only essentials are good electronics and transport mechanism, meters that allow one to make consistently clean low-noise recordings and the Dolby processing circuitry. Separate channel input and output controls can be useful, and auto-stop mechanisms for the motors are nearly always provided these days.

Those intending to do field recordings may find microphone mixing facilities useful, and some machines offer a battery/mains option and are economically oriented towards portable work whilst being equally suitable for use as part of a home hi-fi system.

Most machines are fitted with a headphone monitoring output, and this could be particularly useful for the field recordist; the individual reviews point out whether the headphone amp is suitable for the different types of headphone commonly available (high and low impedance types). If any serious use is expected to be made of this facility, the volume should be easily controllable, which not all machines offer.

It appears that the gods that define public taste have decreed that most current cassette decks should be front-loaders! Most of the latest machines have adopted this layout, which is certainly a welcome alternative to the horizontal or slant loading options, but its almost universal adoption appears to restrict rather than extend choice.

The most suitable format will be dictated by the layout and height of the home installation, but in my experience the top-loaders are most suitable for a system on low shelving, the slant loaders give the most useful compromise, and the front loaders are most practical for high shelf mounting and vertical stacking (watch out for hum fields and heat from power amps here!).

Meters come in a variety of different configurations, and their performance and practicality is discussed within the review text; certainly if the simple 'VU' type is provided, a peak indicator light is a very useful addition. Some of the machines offer facilities that can help improve the sound quality, such as user-adjustable heads to ensure that the machine is properly aligned and continues to work as well as it is capable. Variable bias is also sometimes fitted, and this is particularly useful if one wishes to use the machine with a wide variety of tape types.

While the majority of cassette decks use two heads - one for erase and the other for record and replay - a number of the more expensive machines split the record and replay functions by providing separate or twinned heads.

One indisputable advantage is that a recording can be monitored directly from the tape as it is being made, so it is easy to ensure that everything is going right and avoid later disappointment if something has gone wrong (this is true of nearly all three-head machines although there are one or two exceptions).

The off-tape monitoring also enables instant comparisons to be made against the source being recorded, which can be extremely useful when setting a machine up, adjusting bias or azimuth, or checking for compatibility with different tape types.

Another inherent advantage of separating the record and replay heads arises because a combined head is inevitably a compromise between the two functions, and all other things being equal, separating the heads should enable each to be better optimised for its task and hence provide better overall performance.

But all other things are not necessarily equal. Once again one comes back to the fact that the original Compact Cassette format was never originally intended for hi-fi or professional applications, and it is extremely difficult to find room to squeeze an extra head into the limited number of apertures offered by the cassette housing itself.

Moreover if an extra head is squeezed in, it may degrade the mechanical performance of the deck by adding extra friction. Furthermore the physical constraints on the size of the head or its necessary proximity to another head may cause electromagnetic interference or involve compromises as significant as those the designer is trying to avoid.

So while the 'extra head' is probably very useful, it is not always the panacea that the advertisement copywriter would have one believe. The reviews themselves will draw attention to the three-head facility when offered, and also point out whether any problems were encountered.
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A number of different head materials are used in current machines, including permalloy, ferrite and sendust to name but three. Once again copywriters have the habit of implying magical properties to the particular variation adopted by their manufacturer. But a machine's performance can be limited in all manner of ways, and it is again safer to place one's trust in comprehensive tests that do not rely on specific magic formulae.

Certainly head design is vital, it is difficult to optimise all the conflicting variables, and certain head types do confer certain advantages in terms of saturation, overload characteristics, and head life. But apart from the last, such advantages will be shown up by our testing procedures if they do indeed exist.
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There are three factors that need to be taken into account when trying to maximise the performance of a particular machine.
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1. First the machine should be accurately adjusted electronically so that there are no errors of equalisation or Dolby tracking.
2. Secondly the machine must be aligned to get the best performance out of the chosen tape or group of tapes and the correct type of tape must be used.
3. Thirdly, the tape heads, and to a lesser extent the tape guides, must be kept clean.

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Some cassette types include a cleaning 'leader' section at the beginning and end of the tape, while 'special cleaning' cassettes may also be purchased. Both these can be useful if it is difficult to get at the heads of the machine, but if head access is easy, it is usually cheaper and more effective to use cotton buds moistened with isopropyl alcohol (isopropanol) - several years supply can be obtained easily from a good chemist.

The alcohol should be used sparingly perhaps once a week or before important recordings on the heads, and every couple of months on the other mechanical and guide parts, which tend to get gradually polluted by oxide shedding from the tape.

One topic is perhaps rather in the lap of the gods as far as the initial alignment and setting up of the machine is concerned, being dependant on how carefully quality control was undertaken in the factory (which was probably several thousand miles away) and whether anything has been disturbed in transit.

In our reviews we can only test one sample, or request a second if that proves to have problems, and this cannot be considered any reliable test for consistency. So there is really no alternative for an intending purchaser but to check his own sample before actually buying.

This is best accomplished by making a quick A/B test in the shop concerned, ie making a short recording from a repeatable program-source for say a couple of minutes, and then playing both back simultaneously in synchronisation, switching between them to see whether they sound similar or dissimilar through the same amplifier and speakers. Some differences should be noticeable, and some drop in quality between source and recording is only to be expected, but a well aligned machine with any pretensions should not show any gross disimilarities.

Some shops are equiped to undertake the alignment or re-alignment of cassette decks, but the service naturally costs money, and it is greedy to expect extra quality pre-sales service as well as the best discounts.

One prominent London retailer used to offer the customer the choice of checking and setting the alignment on machines sold at full recommended price 'free', while at the same time offering good discount prices on unchecked machines - an admirably fair arrangement that places the onus fairly and squarely on the purchaser and allows him to decide whether or not to gamble!

In the very first "Hi-Fi Choice" I reviewed some 52 cassette decks. In the early Spring of 1977 the second edition was published incorporating decks from the first book that were then still currently available, together with 35 additional machines.
In this third edition, I have reviewed a further 36 models chosen from 50 submitted by manufacturers. The basic test programme is very similar to that employed in the earlier books, but has been up-dated where necessary, and the subjective test section has been greatly enlarged in the light of experience, so as to help determine the amount of annoyance caused by any particular weakness.

Thus, the entire test programme is split into two well-defined sections: first a comprehensive subjective test programme, and second the laboratory tests. Having completed the entire test programme, much time was spent in trying to correlate the results obtained from the subjective and laboratory tests. Indeed, it was most encouraging that the correlations were, in general, very close indeed.

After each machine had been unpacked, and the instructions perused, it was connected to the mains and the external source and monitoring equipment. A specially devised programme was prepared from very high quality master tapes, the program source tape was recorded at 38 ips with Dolby 'A' processing.

This programme was played back on a Studer B67 professional reel to reel recorder through Dolby 'A' deprocessing, straight into a specially made box which adjusted the source to appropriate levels for feeding into either the DIN or phono (line) input sockets.

The DIN source provided peak program levels of approx 1uA from an appropriate source impedance for interconnection with DIN input sockets. A metering point was also provided, switchable directly in parallel with the recorder's DIN input socket, when required.

A predetermined tone level on the master tape, when played through the system, was brought up to the equivalent of Dolby level, ie 200nWb/m (McKnight Method). The tone level was also measured across the input socket to determine an approximate DIN input impedance, and this was later re-measured very accurately in the laboratory. The phono input sockets were fed from a source impedance of around 4.5k ohms at a peak programme level of around 350mV.
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For each cassette tape recording, the recording level was adjusted so that every tape would be recorded at the same overall flux level, thus allowing each recorder to be tested under identical conditions on record.

The connecting box also included switching to interconnect the recorder's playback from both the DIN and phono output sockets with the monitoring chain. The recorded test tone levels, copied from the original master tape, were replayed before each comparison was made, so that the playback levels were identical to the master tape levels at the comparison switching point.

The selected output from this switch was fed into two Chartwell 450 professional loudspeakers, driven by Quad 405 amplifiers via electronic crossovers.

The test programme recorded on the cassette was also auditioned on both Beyer low impedance and Sennheiser medium impedance headphones, to give a good idea of the performance capability into a variety of headphone types.

Each recorder was then checked using a Sony stereo Electret microphone with speech at 1 ft from the capsules, to determine whether sufficient microphone gain was available, and to estimate the quality obtainable via microphones.

It was felt unjustifiable to carry out this test with studio class microphones, as these would only be used extremely rarely by cassette deck owners.

Limiters were checked for their effectiveness, distortion and other characteristics, by speaking or shouting into the microphone, both centrally and to one side. Finally, after assessing the performance of any other special features, a test was carried out to see if any DIN input or line input noise degradation occurred, and I am sorry to say that almost every model showed at least minor problems here. During the subjective test, a note was made of any Dolby calibration errors.

If the performance was subjectively poor on a manufacturer's recommended tape type, a re-test was carried out with a tape felt to be more appropriate by the author, as the basic properties of the different types of cassette tape had already been determined. The subjective test therefore encompassed a very thorough test of each recorder, but since it is always possible to miss a problem, or to relate the degree of seriousness of any problem to that on another recorder tested much earlier or later, it must be realised that the laboratory tests are vital to correlate with the listening tests.
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