The principles of infrared simultaneous interpretation system is to carry out language distribution by the infrared. Due to its high confidentiality, the infrared transmission is the most advanced and prevalent way in wireless simultaneous interpretation system now. Presently, the infrared simultaneous interpretation of various brands all over the world can be divided into two categories, using two different frequency bands for the infrared transmission, one is BAND 2: 45K - 1MHz, and the other is BAND4: 2MHz - 6MHz. Figure 1 shows the details. The differences between the two bands are as follows:

1) The infrared transmission systems by the BAND 2
are subject to the interference of HF (high frequency) drived lighting(i.e. Fluorescent lamp). The HF drived lighting gives off the HF interference harmonics, as show in figure 2. within 2mhz, the hf drived lighting gives off various harmonics frequencies, which interferes the infrared transmission in the same ranges severely. However, for the infrared transmission system using BAND 4, the energy of the interference harmonics from the lighting has attenuated to a neglectable level. The infrared transmission can perfectly avoid the ambient lighting interference, and make the infrared simultaneous interpretation system work smoothly and noise-freely.Figure 3 illustrates the principles.

2) The bandwidth of BAND 2 is less than 1MHZ,whereas BAND 4 is 4MHz, thus the electroacoustic features, such as frequency

response, SNR and dynamic ranges of the infrared simultaneous interpretation system using BAND 4 is much better than those using BAND 2.

Generally speaking, the infrared language distribution system using BAND 4 has better transmission performance, higher anti-jamming abilities and more perfect audio quality.