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SUMMARY

Now that you've finished chapter 6, you should be able to describe the seven most common magnetic tape recording specifications and how to measure each specification. The following is a summary of important points in this chapter:

The SIGNAL-TO-NOISE RATIO (SNR) is the ratio of the normal signal level to the tape recorder's own noise level measured in dB. The higher a recorder's SNR, the wider the range of signals it can record and reproduce.

SNR IS STATED IN ONE OF THREE WAYS based on how it was measured. If you don't know the way it was measured, you could be misled.

A recorder's FREQUENCY-RESPONSE specification is sometimes called its bandwidth. It tells the range of frequencies a recorder can effectively record and reproduce. Factors that can degrade a recorder's Frequency response are an improper bias level setting, reproduce head gap, or tape transport speed. Also, failure to clean the heads and the tape transport can cause poor tape-to-head contact.

HARMONIC DISTORTION is the production of unwanted harmonic frequencies when a signal is applied at the recorder's input. The primary harmonic distortion in tape recorders is third order harmonics. It's measured with a wave analyzer. You can reduce this distortion with proper preventive maintenance and periodic performance tests.

Good PHASE RESPONSE means the recorder can reproduce complex waveforms such as square waves without distortion. The best way to check a recorder's phase response is by recording and reproducing a square wave and checking the output on an oscilloscope.

FLUTTER results from non-uniform tape motion caused by variations in tape speed. The tape speed variations are caused by design and machining deficiencies in the rotating and fixed parts of the tape transport.

TIME-BASE ERROR (TBE) is the time-relationship error between two or more events recorded on and reproduced from the same magnetic tape. It causes TBE jitter, which introduces noise or loss of accuracy where precise timing relationships exist between two or more signals.

SKEW is the time difference in microseconds between the tracks on a multi-tracked tape recorder. Fixed or dynamic skew can happen when one of the tracks on the multi-track head leads or lags the track next to it. Fixed skew errors only show up when you record on one recorder and reproduce on a different recorder. You can minimize fixed skew by adjusting the recorder's electronics and aligning the heads. Dynamic skew errors are caused by worn or sticking tape transport guides or by warped magnetic tape.




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