Abstract: A system with improved signal-to-noise ratio for digitizing a representation of an analog condition comprises two oscillators for generating high frequency digital pulse signals, the frequencies of which are harmonically related one to the other. One of the oscillators responds to the analog condition to cause a shift in phase in its digital signal to cause phase differences between the digital pulse signals. The phase differences include quantizing errors having energy from D.C. to one half the frequency of said digital signals. A phase detector detects the phase differences. The detected phase differences are applied to a low-pass filter to produce a signal representative of phase error in a frequency band of interest. A phase modulator modulates the phase shifted digital signal in response to said signal representative of phase error to enhance the phase difference in said frequency band of interest.

Abstract: A real-time monitor which displays analog representations of digital seismic data having been recorded on magnetic tape such that adjacent seismic traces are partially overlapped, whereby the appearance of an error is enhanced and is disclosed. The monitor display is controlled by a computer which may be of a type similar to computers used in the seismic data storage system for other purposes so that it may serve as a back-up computer. This system is implemented by incorporating into magnetic tape data storage drives read-after-write circuitry so that the data put on the tape can be read off the tape immediately thereafter and used to control the monitor means. In this way, the monitor is in fact operating in real-time and operates on precisely that data which in on the tape; thus any errors displayed on the real-time monitor include any errors made in the actual recordation of the data onto magnetic tape.