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What will happen to the audio signal if the tape head gap is increased during playback?

Asked 1319 day 18 h | Viewed 3303 times | Updated 1317 day 23 h |

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Gravatar photo Rajitha Nair

If the tape head gap is increased during playback compared with the recording process, what will happen to the audio signal?

3 Answers

  1. Answered: 1294 day 17 h (1) | Permalink

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    Gravatar photoguest

    Play back gaps are always narrower than record gaps on heads that are dedicated for the purpose (IE 3 head machines). The recording process can be visualised to occur on the trailing edge of the gap. It is at this point the head looses its influence on the tape and the bias field diminishes. This is different to the reproduction process which is limited in resolution by the gap width.

    As the previous answer suggested the HF replay bandwidth is reduced with increasing play head gap. At the frequency that the gap is 1 wavelength wide, the head recovers zero signal. (Naturally as the frequency further increases the recovered signal increases and falls again exhibiting comb filtering effects. Audio machines only use the spectrum below the first zero naturally).

    This is one of the many reasons that professional tape machines pulled tape at 15 or 30 IPS. A high tape speed proportionally increases audio wavelengths and gives the same gap head a higher bandwidth.

    A worn out head has a rapid increase in gap width and a sudden fall of in recovered high frequency level. Reproduction heads are actually at their most efficient just before they fail as at this point the tape flux is bypassed minimally by the worn pole pieces. The Full Bench

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  2. Answered: 1317 day 23 h (0) | Permalink

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    Gravatar photoJustin Vencel

    I am definitly not an expert on tape...not by a long shot.  So here it goes.

    In order for the tape head to be able to pick up signals of short wave length (high frequencies), the gap between the head and the tape must be smaller than the actual wave length of the highest signal frequency.

    Typically, tape gap widths are somewhere between 3µm to 8µm.

    Armed with this knowledge I would think that if the gap between the tape head widens during playback then the head will fail to pick up the recordings high frequencies off the tape.  Imagine grabbing the high frequency knob and turning it down.  (A popular DJ trick)

  3. Answered: 1262 day 23 h (0) | Permalink

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    Gravatar photoguest

    An everything in life, the best solution is a "Compromise"

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