NO; it is proportional to the product of the signal voltage (voltage amplitude) times the period or time length of one cycle of the wave. Lower frequencies require the cutting head to keep moving at the same rate in one direction for a longer time, so the resulting groove is wider as the frequency is lowered (for any given amplitude).**
The thing you need to understand is that the instantaneous voltage output of the cartridge depends on the RATE at which the stylus is moving (not its physical displacement from rest). The cartridge is an electromagnetic generator, and the rate of stylus motion determines the output voltage.
To cut bass tracks on a vinyl record that will make the cartridge put out the needed voltage, the low-frequency excursion of the groove would be huge, since the master cutting head would have to maintain a high rate of movement for up to 25 milliseconds in each direction. The resulting grooves would be so wide on the record surface that a music track with low bass might cut the playing time to 3 or 4 minutes on each side of a 12-inch record. Another issue is that it would be very hard to make a cartridge that would track LF grooves that wide.
The only solution to this is to de-emphsize (reduce the signal voltage to the cutter head) at the lower frequencies. The lower the frequency, the worse the problem, so a roll-off filter is used when cutting the record. This is one of the functions of an RIAA equalization filter.
The phono preamp must then boost the low frequencies coming from the phono cartridge back up to their original relative level for playback using an inverse RIAA filter.
The RIAA filter also boosts the high frequencies during recording. This establishes a high signal-to-noise ratio on the record surface. When the high frequencies are de-emphasized by the RIAA filter during playback, the background noise is also reduced.
You should read the Wikipedia entry on "RIAA EQUALIZATION" which explains this in specific detail.
**- (for similar reasons, the physical excursion of a speaker cone is inversely proportional to frequency)
Edited by commsysman - 8/10/12 at 5:54pm
Originally Posted by Lawrence001
Everywhere I look the explanation given as to why de-emphasis of low frequencies is necessary is that low frequencies create bigger modulations and in the interest of extanding amount of music that can be stored we de-emphasize the lower frequencis. But how is frequency relevant here, isn't it just the amplitude of a sound wave that determines the amplitude of the groove on the disc?