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Frequency characteristics of RIAA
The RIAA frequency characteristics will be described by a transfer formula A. This function has an inverse Laplace transform of A_inv=1/A. Typically, a shift of 20 dB is needed at 0 Hz, and a correction factor of one-tenth is used. The transfer function will look like Laplace=(s*T1+1)*(s*T3+1) and its inverse Laplace transform will look like Laplace=(s*S*T3+1)*Laplace.
This RIAA-defined curve can be complied to within 0.1 dB of 20 Hz to20 kHz. THD and noise data are also included in Table 2. A RIAA-compliance cartridge's response spectrum should be flat. However, slight deviations can be detected by the human ear.
The RIAA characteristic was first developed for the US recording industry, but it was quickly adopted around the world. It became part IEC 98 standard in 1964. IEC 60098 (now IEC 60098) defines RIAA frequency characteristic and describes characteristics of microgrooves records.
RIAA channel separation
The RIAA uses a standardized method to determine channel separation. The SG-5070 adapterboard has four disc options. The RIAA equalization produces a flat response spectrum. Any deviations from this spectrum can be easily identified by the eye. The RIAA also employs an output filter to reduce high-frequency noise.
Frequency response to RIAA
In 1953, The Recording Industry Association of America (RIAA), introduced the first equalization curve. Before this, several curves were used for measuring a record's response. These curves were no longer used, but the RIAA is now the standard.
The RIAA curve can be implemented easily. Historically, hifi preamplifiers featured built-in phono amplifiers with RIAA characteristics. However, most hifi designs today do not have phonograph outputs. You can still buy add-on phono amplifiers with the RIAA standard curve. Modern turntables come with built-in amplifier circuits. There are also phono-preamplifiers that can accommodate a wide range RIAA curves.
Stereo Lab equalization can be used as a similar technique to RIAA. This equalization technique employs a slightly under-damped 4th-order filter. It also employs a turnover at 20Hz. As the frequency drops, it falls off quickly.