﻿ RIAA equalization

RIAA equalization

The cutting characteristics ( cutter and characteristic) is a measure of the lateral deflection of a record groove. For a given rotational speed of the disk and the moving speed of a given frequency, known as Fast, the scanning needle is not linear, but is adapted to improve the sound.

The peak

The peak value of the moving speed is referred to as a fast. This peak value is greater, the greater the deflection ( deflection in the amplitude ), and the higher the frequency of the recorded sound vibrations.

To obtain a linear frequency response as possible, was cut in the purely mechanical scanning with a constant velocity. This resulted with decreasing frequency is always greater Rillenauslenkungen, whereby the required space on the vinyl would have to increase. On the other hand, the Rillenauslenkung would be so small that the useful signal would when playing in the noise frequency increases. Accordingly, a sound recording with a constant speed over the entire frequency response is not practically feasible.

For this reason one has defined the cutting frequency response according to the recommendations of the RIAA and the German standard DIN 45 541. In this case, the recording does not take place at a constant speed, but, in principle, with a constant displacement in accordance with DIN IEC 98, which corresponds to an increase with the frequency fast. The characteristic of the N78 - record had to DIN 45 533 at 15 kHz by approximately 4 dB less treble boost.

Subdivision

The cutting curve is divided into three sections:

• One below 50 Hz
• One between 50 and 500 Hz
• A 2120-15000 Hz

In these sections, the deflection is constant. The disadvantage is that the division runs in two sections continuously into each other.

Furthermore, the deflections are slightly raised in the low frequencies in order to obtain a higher Signal to noise Ratio. The exact profile of the cutting curve is determined by the above -mentioned transition frequencies or time constants. The time constant can be calculated from the cross-over frequency f according to the following formula:

Table 1 lists all the important data of the cutting frequency response are summarized. At low frequencies, the maximum deflection is determined by the groove spacing, at high frequencies by the radius of curvature of the needle at the supporting surface. For high and low frequencies for the smallest deflection is bounded by the required Signal to noise Ratio ( noise).

To get a very good idea, with what speed you cut plates, record type, speed and velocity are compared in Table 2.

With the newly developed electromechanical transducer, it was possible to optimally adapt the sampling conditions and the statistical distribution of the amplitudes of music and language the frequency response of the cutting curve and then to equalize electric.

The cutting characteristics applicable in Germany for all records produced. Foreign recordings on vinyl often have other cutting curves on which the Schneidkurvenentzerrer can be switched ( NAB, RIAA: 3180/318/50 microseconds, BBC: 3180/318/25 microseconds, FLAT: 3180/319/0 microseconds ). The various cutting curves are different only above 1 kHz.