As the central equipment of the sound system, the technical performance index of the sound console plays an important role in the whole sound system. Like other equipment of sound system, the performance index of sound mixing desk has two types: basic index and special index. Basic index is the technical index that all sound equipment place is GENERAL, special index is the technical index that points to the function place that decides according to mixing station peculiar.
The main technical performance indexes that have great influence on the work of the mixing console are as follows:
Gain is the logarithm of the ratio between the output signal voltage of the mixer and the input signal voltage, or expressed as the difference between the output level and the input level, denoted as K, then K=20lg Uo/Ui (Equation 1), where Uo is the output voltage and Ui is the input voltage.
The output level standard of the mixer is the line level, which is 0dB. 0dB is equivalent to the voltage needed to obtain 1mW power on the load of 600 ω (0.775V) and take the logarithm as the benchmark, sometimes also expressed by 0dBv, dBv voltage reference value is 1V, with 1kω as the load. There are two kinds of input of the mixing console. One is the Line input (Line In), whose level standard is 0dB; One is the microphone input (Mic In), and its level is -70 ~ -50dB, which corresponds to the actual sensitivity of the microphone.
From the perspective of the line input of the mixing console, the gain of the mixing console is 0dB. Although amplification is also found inside the mixer, this is mainly to compensate for signal attenuation during tuning (sound quality processing). For microphone inputs, the console must provide sufficient gain to raise the microphone low-level input of about -70 db to the console output of -10 ~ 0dB, which is standard for power amplifiers or other sound equipment.
Generally, there are two kinds of gain of mixing console: rated gain and maximum gain. The rated gain of microphone input should not be less than 70dB, and the maximum gain can be more than 90dB. The rated gain of the line input is 0dB, and the maximum gain is over 20dB. Some mixer output level is 0VU(or dBvu), 0VU is equivalent to +4dBm(1.23V), the gain also has the corresponding change.