The theory of playback of Vynyl LP recordings is well documented in several professional publications. it is in fact quite complicated. I will try to explain it in simple terms. Fitst, the frequency response on the recording is done to the RIAA recording curve, where the low frequencies are reduced in level and the high frequencies boosted to follow this frequency curve or frequency response. On playback, the frequency response of the Pick-Up Pre Amplifier is the exact opposite providing the RIAA Equalisation or Compensation to end up with an overall flat playback frequency response of the original recorded material. Unfortunately, there are losses in this process, and this is where things get tricky. The recording is done with a "Chisel" shaped stylus having fairly sharp corners. The Playback Stylus is either Spherical (Round) or Elliptical and cannot follow the original cut groove exactly which will cause some loss of high frequencies. A loss which differs from cartridge to cartridge, and dependent on the stylus diameter and type. The stylus assembly in the Pick-Up cartridge also have a mechanical resonant frequency, usually at a frequency higher than the highest frequency of interest, but in some cases involving inferior products unfortunately not. Electrically, the coil on a conventional Moving Magnet cartridge forms an inductor. The technique for best playback results is to "Tune" the cartridge at a suitable frequency by considering the cartridge coil as an inductor, and the cable on the Pick-Up Arm together with the input capacitance of the Pre-Amplifier as a parallel tuned circuit which will resonate at a particular frequency. Better types of Pre-Amps have selectable C to allow this to be done. The tuning will result in a distinct peak in the high frequencies which is then damped out by resistive loading to give an overall flat playback frequency response up to a maximum high frequency determined by the stylus diameter, and the stylus assembly in general. Very tricky to do and requires patience, basic test instruments and a calibrated frequency response test record. By the way, test records only last a few playbacks before they suffer loss of high frequency information. Fortunately, most reputable Pick-Up Cartridge manufacturer do specify the optimum capacitive and resistive loading for each type of cartridge. These specifications only hold good provided the cartridge is fitted with the correct original manufacturers stylus assembly, and that this is in "Good Health". For brand "X" aftermarket stylus assemblies, the situation could be completely different, my advise, for replacements, even if it costs more, purchase the proper manufacturers replacement stylus assembly.
