THE quality of a finished disc will be no better than the instrument which supplies program material to the amplifier. For that reason, a brief description of sound sources is given here.
There are 5 principal types of microphone in present-day use :
Carbon, ribbon or velocity (the terms are interchangeable), condenser, dynamic or moving coil, and crystal (sound-cell or diaphragm type).
Table 8-1 summarizes microphone characteristics. Fig. 801 shows the directivity of a ribbon microphone.
Table 8-1--Microphone characteristic chart.
Fig. 801-Directivity pattern of a ribbon microphone.
Phonograph pickups, important in re-recording and dubbing, are described in detail in Section 13.
Tuners and other amplifiers used to feed the recording amplifier
should have good frequency response and very low noise level. Output impedances must be correct. For AM reception in areas where only local broadcasts will be recorded, special high-fidelity tuners, usually of the band-pass t.r.f. type, are desirable. These have better frequency range and lower distortion than superheterodynes, and they are almost universally used by professionals. Several are on the market as kits at reasonable prices.
Fig. 802-Typical diaphragm type crystal microphone.
Fig. 803-A typical dynamic micro-phone.
Fig. 804- A typical ribbon(velocity) microphone.
Fig. 805-Typical sound cell crystal microphone.
They usually have no audio sections and are fed directly to the recording amplifier input. See Section 12.
With the advent of FM, the recordist has an incomparable opportunity to make excellent records. The output of a good FM radio or tuner has less distortion and better frequency range than all but the best wire lines and should not even be mentioned in the same breath as AM radio. Records made of "live" FM programs will sound every bit as good as-and sometimes better than-those made in the recordist's own studio, and the opportunity for collecting a library of music by this means should not be passed by. Carefully handled and played on a light pickup with good needles, they will last long and will have no annoying surface noise.
In summation, any sound source should have optimum frequency response and lack of noise and distortion. Where equalization is necessary, it should be accomplished within the device or between it and the recording amplifier, never within the amplifier.