A new technique, using empirical relationships between median grain size and density and velocity to calculate proxy values for density and velocity, avoids many of the problems associated with the use of well logs and shipboard measurements to construct synthetic seismograms. This method was used to groundtruth and correlate across both analog and digital shallow high-resolution seismic data on the New Jersey shelf. Sampling dry vibracores to determine median grain size eliminates the detrimental effects that coring disturbances and preservation variables have on the sediment and water content of the core. The link between seismic response to lithology and bed spacing is more exact. The exact frequency of the field seismic data can be realistically simulated by a 10-20 cm sampling interval of the vibracores. The estimate of the percentage error inherent in this technique, 12% for acoustic impedance and 24% for reflection amplitude, is calculated to one standard deviation and is within a reasonable limit for such a procedure. The synthetic seismograms of two cores, 4-6 m long, were used to correlate specific sedimentary deposits to specific seismic reflection responses. Because this technique is applicable to unconsolidated sediments, it is ideal for upper Pleistocene and Holocene strata.