When you talk about the magnetic tape and recording, is it the pressure or frequency that is being recorded? Are pressure and frequency interrelated?
Sound consists of pressure fluctuations. The stronger those pressure fluctuations, the louder the sound. The rapidity with which the air goes between a pressure increase and a pressure decreases determines the frequency of the sound and the pitch that we hear. So the extent of the pressure fluctuations, their amplitude, determines the sound volume while the number of pressure fluctuations each second, their frequency, determines the sound pitch. The tape recorder detects both and records both. The louder the sound, the deeper the recorder magnetizes the tape. The higher the frequency of the sound, the more often the tape recorder reverses the magnetization of the tape’s surface.