RIAA Curve

For the same sound level, a low frequency requires a larger groove which gives two drawbacks:
- Less recording time
- Difficulties for the cartridge to follow it and thus, higher distorsion

At the other end of the spectrum, the contact between the stylus and the groove makes noise, a high frequency noise. By increasing the high frequencies level during recording we can obtain a better signal/noise ratio as the noise is reduced by the playback curve.

The RIAA (Recording Industry Association of America) introduced the original RIAA equalisation characteristic during the 1960’s. Before this became available several other curves did exist, but since the RIAA curves’ introduction they have been replaced

To obtain the original RIAA curve the following equation is used:

Where:
f=frequency
t1=treble time constant, 75uS
t2=medium time constant, 318uS
t3=bass time constant, 3180uS

In 76', IEC introduced a modification of this curve by introducing a new time constant that modifies only the extreme bass. It is known as the RIAA/IEC curve.
This correction has never obtained a big success, the original RIAA curve is still the most widely used.

To obtain the revised RIAA IEC curve the following equation is used:

Where: t4=extreme bass time constant, 7950uS

The RIAA reproduction curve:

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