 The fidelity of a sound recording system depends essentially upon the frequency range and quality of the cutting head, the stability of the turntable, and the type of disc used, for all other components of a quality recording system will in general be capable of giving more than satisfactory fidelity.In general, the cutting head governs the frequency range of the system, and consequently many manufacturers specify the frequency response of the cutting head rather than that of the entire system. Any wobble in the turntable or any variation in its speed will result in unsteadiness of tone. This may not be noticeable in certain types of recordings, such as of swing music but will result in unsatisfactory recordings of classical selections. The 60-cycle synchronous motor which is generally used to drive the turntable should be mounted in such a way that motor vibration cannot reach the, turntable or recording head. The motor speed is considerably greater than that desired for the turntable, and consequently a speed reducing mechanism must be employed. One popular drive method for portable systems is based upon the use of rubber-faced rollers which drive the rim of the turntable by friction. If the pressure on the roller is released immediately after each recording to avoid forming a "flat" on the rubber roller, entirely satisfactory results can be obtained. Another popular mechanism is the steel ball friction drive. The turntable itself should be fairly heavy, with most of its weight concentrated in the rim In order to obtain maximum fly-wheel effect and thereby smooth out vibrations and variations in speed. In a good portable recording system, the greatest source of noise is at the point of contact of the cutting needle with the record disc, and this varies with the type of recording disc used.
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