APPARATUS AND METHOD FOR AUTOMATIC ADJUSTMENT OF READ AMPLITUDE THRESHOLD IN A DIGITAL TAPE DRIVE

A digital audio tape (DAT) drive (100) for use with computer systems includes a circuit (130) and a corresponding method for setting the read amplitude threshold for testing written data to determine whether it has a sufficient magnitude to be successfully reproduced. The threshold is set by writing a predetermined data pattern onto a segment of tape (118) to be written with actual data. The predetermined data pattern is selected to comprise pseudo-random ones and zeros so that the reproduced data signals comprise a wide range of frequencies and corresponding amplitudes so that the average amplitude can be determined. The reproduced data signals are sampled and digitized, and the digitized samples are provided as inputs to a microprocessor (250). The microprocessor (250) discards approximately one-half the lowest magnitude data samples so that low amplitude signals caused by media flaws in the test portion of the tape (118) do not affect the method. The microprocessor (150) averages the remaining data samples and computes a threshold value corresponding to a fraction of the calculated average. The computed threshold value is applied to a comparator (256) and is compared with the magnitude of reproduced data signals when reading actual data while performing a read after write operation. The detection of a data signal of lower amplitude than the computed threshold causes a low amplitude signal to be generated and causes a controller (112) to rewrite the corresponding data on a different section of the tape (118).