A Method of Reducing Amplitude Distortion in Engraving Lateral Electrical Transcriptions

A method was developed to minimize the amplitude distortion that arises from the failure of the curved path of the reproducing head to coincide with the straight radial path of the cutting head. A mathematical analysis of the vectors involved in both recording and reproducing 16″ electrical transcriptions was the first step. An approximate solution to the problem was found in an adjustment of the orientation of the track of the carriage of the recording head to permit the cutting needle to lead behind the conventional radial path for the first half of the recording time and then lag it for the remaining half. The new path of the cutting needle is a straight line at a seven degree angle with the conventional radial path, crossing the latter at the center of the usual recording zone. A secondary axial adjustment of the cutting needle in the recording head is necessary to keep the face of the needle perpendicular to the direction of movement of the disk beneath it. No change is necessary in the standard reproducing apparatus. Harmonic analyses of electrical reproductions of sine waves recorded by this method have shown an over-all reduction of amplitude distortion from 8 percent, to less than 2 percent.