PHONOGRAPHS 239 



Another source of nonlinear distortion is due to a deviation in tracking/^ 

 commonly termed tracking error. The angle between the vertical plane 

 containing the vibration axis of the pickup and the vertical plane containing 

 the tangent to the record is a measure of the tracking error. If the vibra- 

 tion axis of the pickup passes through the tone arm pivot, the tracking 

 can be zero for only one point on the record. The tracking error can be 

 reduced for the entire record if the vibration axis of the pickup is set at an 

 appropriate angle with the line connecting the needle point and if the 

 length of the tone arm is suitably matched to the distance between the 

 tone arm pivot and the record axis. For a tracking error of 15° the dis- 

 tortion is approximately 4 per cent. However, by the above expedient 

 the tracking error can be reduced to ±5°. With this tracking error the 

 distortion is negligible. 



Another source of nonlinear distortion is due to the finite size of the 

 stylus or needle point. The curve traced by the center of the needle slid- 

 ing in a sinusoidal groove is not sinusoidal. This distortion may be re- 

 duced by reducing the size of the needle point. It is interesting to note 

 that this distortion is greater in vertical cut records than in lateral. The 

 push-pull effect of the lateral record tends to reduce the second harmonic 

 distortion. 



Another source of distortion is due to the lack of correspondence between 

 the linear groove speed in the recording and ultimate reproduction. This 

 type of distortion is termed " wows." This may be due to a nonuniform 

 speed of the record turntable during recording or reproduction, misplace- 

 ment of the center hole or configuration distortion during the processing. 

 In general, the major source of " wows " is due to nonuniform speed of the 

 reproducing turntable. 



The record surface noise, in the absence of any signal, is one of the factors 

 which limits the volume range and the frequency range of phonograph 

 records. The amount of surface noise for a given record is proportional 

 to the frequency band width. In order to reduce the surface noise to a 

 tolerable value it is usually necessary to limit the high frequency range. 

 A method for decreasing the efi^ective surface noise consists of increasing 

 the amplitude of the high frequency response in recording and introducing 

 complementary equalization in reproduction. The volume range of a 

 phonograph record, in general, does not permit recording the full range 

 of a symphony orchestra without some compression. To offset this com- 

 pression complementary expansion may be introduced in the reproduction. 



i^Olney, Benj., Electronics, Vol. 10, No. 1, p. 19, 1937. 



