Cassette technology - Understanding tape recorder specifications and feature lists

Technical Specifications

Frequency response
The frequency range that a tape recorder can record and playback while still showing a reasonably flat response. Theoretically a tape recorder can record any audio signal it is given regardless of its frequency, in reality however it will only function properly within a given frequency range and within that frequency range show variations in volume from the ideal. The upper range a recorder will work with is usually limited by filtering to minimise the effects non-audible high frequency signals will have on audible signals and to give signals within the audible range more bandwidth, on some cassette recorders and old reel to reels this is not done since the technical specifications of the recorder are so bad that there is no danger of any high frequency signals being recorded anyway.

There are 2 types of FR tests that you will see quoted, fully weighted and DIN. A fully weighted test on a good fairly recent cassette recorder might give you a frequency range of say 15Hz to 15kHz +/- 1dB for recording on chrome tape, that means that any sound between 15Hz and 15kHz recorded onto a chrome tape will vary less than 2dB in volume from the real level of other sounds recorded onto tape in the same specified frequency range. Note that this does not mean that the recorder does not record sounds outside of that range nor does is imply that recorded sound will vary only 2dB from the sound input into the recorder, cassette recorders in particular have a notoriously limited Dynamic Range and thus will always compress the volume of whatever sound that you record onto them, however this figure guarantees that the variation in volume will be no more than 2dB and that while it will probably record frequencies much higher and lower than that, the variation in volume will be more than 2dB.

This is an unnecessarily stringent test given that at the upper extremes of the audible spectrum we will not clearly discern volume changes of less than 4 to 5dB unlike the midrange where we can discern changes of less than 1dB, and most manufactures quote a DIN test which has more give at +/- 3dB (e.g. a 6dB variation) which would give the same recorder a FR of 15Hz to 22kHz. The plus of a using the DIN test is that its parameters are nailed down like anything else from Deutsches Institut für Normung and since the weighted tests may vary a little bit from manufacturer to manufacturer the DIN tests are a better basis for comparison between different makes even if they give a little bit more romantic view of the recorders capabilities than the other tests. Having both means that the DIN test shows a fuller picture of the recorders capabilities in the upper registers while the fully weighted test guarantees that the variations within the more critical midrange are nothing outrageous. Be careful though, some weighted tests are published at +/- 3dB, this is naughty, and is usually only done with budget decks or mid-range recorders that have the feature set of a decent recorder but are built around a budget tape transport to save costs.

Tape Pre-Sets
Although all cassette tapes are meant to follow a certain specification for equalisation requirements and optimal bias they do in the real world vary quite a bit, so each recorder is aligned at the factory to optimally function with a certain brand and type of tape. This is usually either a tape from the manufacturer of the device, their business partners or a market leading brand and type in their home market. This does not mean that you cannot use other tapes, just that it will be less optimal, recorders with ATC will automatically adjust to whatever tape you put into the recorder and recorders with variable bias and record calibration will allow you to do it manually.

All cassette recorders utilise AC bias with the sole exception of very low budget models from the 60’s and 70’s, such as children’s toys, that used permanent magnets. In a units specification the only interesting value in regards to the bias is really the frequency of the signal, the higher the better. High frequency bias signal circuits are slightly more difficult to design and more expensive to implement properly so really only seen on the top of the range recorders, mid and most high end recorders usually had bias frequency of no more than 80 kHz but reference class designs often had bias frequencies of over 100 kHz.

Feature lists

How a cassette is loaded into the recorder. Most cassette recorders use a lid loading system whereby a lid (or door) of the cassette mechanism has a slot that you slide the cassette into, or in cheaper models at the least 2 plastic holders on the inside of the lid that you slide the cassette into, then when you close the lid the cassette slots onto the drive gears that turn the tape and the tape heads lift up to the cassette when you press play or record. The very cheapest cassette recorders use a direct load system where the lid, if there is any, is just to keep out the dust away from the recorders heads and the user slots the cassette directly onto the gears, this is inherently cheaper since the lid loading system while simple requires a little bit more materials and also that the lid assembly be of at the least reasonable construction quality and firmness otherwise the lid will resonate.

The direct load system has another plus which is why it is sometimes seen used on more expensive models, the cassette is held in place much more firmly than with the lid system, this minimises resonances from the lid assembly and from the cassette shell itself, furthermore if directly loaded the cassette mechanism can be built directly onto the recorders fascia which enable a much more rigid construction while still being reasonably cheap, but more rigidness again helps with resonances. The lids on the more expensive cassette recorders had become quite complex constructions with internal damping of the structure and external damping for visual effect so in the late 70's a number of manufacturers such as Sanyo? and Dual went back to a direct load system in their mid-range cassette recorders and it did show in the sound quality.

There are other more rare versions of a loading systems around, tray loading similar to CD players being the most popular, in most cases it is mechanically similar to lid loading except that in this case the mechanism is mounted on the bottom of the recorder, in some high end products this is a variant of direct loading with the entire cassette mechanism being mounted into the tray. The only benefit of using tray loading is space, recorders that use trays can be less than half the height of a normal system. Slot loading is only really used on car audio products except in exceptional cases because it requires a mechanism to move the cassette inside the recorder which is unreliable and causes some issues with resonances, on top of being more expensive to implement than lid loading. Cassette recorders with bulk cassette loading capabilities of some sort have all kinds of ingenious and not so ingenious was of feeding a mechanism with tapes but these are rare.

Note in feature lists for recorders with 2 or more wells this column is skipped since all known multi-cassette recorders have lid loading.

Simply specifies if the transport controls of the deck are either Manual in which case when you press down a button and the heads and rollers of the tape mechanism are moved towards the cassette by the mechanical force generated by your fingers or Logic in which the heads and rollers are moved towards the cassette by logic control where there is no mechanical connection between the transport and the controls. The difference is mostly psychological, as far as audio performance is concerned the difference is minimal except that the logic based transports are usually slightly more rigid and better decoupled mechanically from the outside hence should perform slightly better in a real world situation.

Playback only tape machines have one head that reads information off the tape, recorders have 2 heads, one that either reads or writes information off the tape depending on if you are in record or playback mode, and an erase head that is in front of the record/playback head in the tape path and erases the tape so it can safely be recorded over by the record/playback heads. More expensive models have 3 heads where the recording and playback heads have been separated to enable both to function at once, by placing the playback head behind the record head in the tape path you can listen to the recording while you are recording, this is important for quality control and thus popular with professionals and serious amateurs. Note that on cassette recorders there is usually not enough space for 3 separate heads so the recording and playback heads are a sandwich, i.e. they look like one head but are actually 2.

Open reel recorders can have more heads, for instance a 4th head for biasing the tape separately from the recording head to minimise the influence of the biasing signal on the music signal, or 6 heads on auto reverse recorders so that a tape can be reversed on the spot without having to reverse and realign the 3 heads like you need on a cassette recorder. Dual Well recorders usually have one playback deck and one that records, thus you will see figures like 2/1 for heads, that simply means that the recording deck has a combination record/playback head and an erase head while the playback deck only has a playback head, a high end dual deck would have a figure like 3/1 or if both decks can record 3/3, except in very few cases were one deck is worse specified than the other and you will see 3/2, triple well decks will display 3/3/3 and so on.

In early recorders a button that when pressed in recording mode disconnected the input signal from the recording head and thus created silence on the tape. In most cases the muting function is only active while the button is held down although in few cases it was an on/off switch. The AutoRec mute was introduced at the same time as the music search function, but the AutoRecMute simply creates a 4 second silence on the tape after it is pressed although most allow longer mutes if you hold the button down, this is because 4 seconds is the minimum length of silence needed for the music search function to work in cassette recorders that spooled at very high speeds (more than 100x). The main difference between that and older mute functions is that AutoRecMute in most cases also works when the recording is paused.

Specifies if the recorder came with a remote or had the possibility to be remote controlled. Most recorders neither came with a remote nor the possibility to use one but a still significant number had either a built in IR receiver so that an optional remote controller could be bought or more commonly has some sort of a system link that allowed the recorder to be remote controlled via a system hub that was usually an amplifier or in some cases a timer.

The recorders that had an optional remote can be used with just about any generic remote on the market, it is just a matter of finding out which pre-set codes work with the recorder. System links are usually simply a one strand/wire cable that is hooked from the hub to the recorder; it is easy to make up such a cable if one cannot be found. In a few cases in particular with mid-high end Sony recorders of a certain vintage the recorder has a serial computer interface that can then be controlled by either a computer or more commonly by a home installation/multiroom system but they commonly have such since that is the standard for controlling A/V amplifiers.

Next Page : Automatic Tape Calibration

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The site was last compiled on Sun Nov 10 2013 at 9:15:00am