Analogue Recorders - Projecting criteria

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Constant ribbon speed: this characteristic is necessary in order not to have variations in the frequency content compared to the original sound. If the ribbon accelerates, the polarity variations of the induced current take place more quickly, which generates frequencies that are higher than those contained in the original signal. If the ribbon slows down, the exact opposite occurs.

Use of appropriate recording levels: it is absolutely necessary to record at a level which is high enough to cover up background hiss. Such hiss comes about because when the particles are not magnetized, they arrange themselves randomly and, even though this guarantees almost a complete lack of magnetic field, some of them will have a common direction. This generates a current which, though being small, is nevertheless audible resulting in a background hiss sound. It is also important not to have excessive recording levels so as to avoid distortion. The latter is generated because the number of particles contained within every unit of ribbon is limited. Therefore, if an excessively high current is applied to the head, the number of magnetic particles is not sufficient to reproduce such an intensity. In other words once all the particles are disposed in the same single direction, polarization cannot go any further, thus generating distortion.

Constant ribbon tightness: this is needed to make sure that the ribbon doesn't stretch so that its physical characteristics, and those of the stored signal, remain unaltered.

Minimization of lateral movements of the ribbon: lateral movements of the ribbon may vary unpredictably the quantity of surface exposed to the head, with a consequent alteration of reproduction.

Minimization of ribbon wear and tear: certain mechanical expedients are used in the construction of professional analogue recorders. Lets take a closer look at these expedients using a professional 2-track reel recorder as our example.

  • Tension reels: their function is to compensate for the ribbon's tension variations during the rolling.

  • Guides: prevents lateral movements of the ribbon.

  • Tape lifters: actioned either when the recorder is still (stop) or during fast forwarding and rewinding.

  • Capstan

  • Pinch roller: maintains the ribbon's rolling speed as constant as possible.