The T4 electro-optical device is the heart of the compressor and its gain reduction characteristics. Its unique characteristics affect the overall sound and character of the LA-610. In addition to the compression curve, the combination of the EL panel and the photo-cell determine the attack and release characteristics of the LA-610. This is one of the most important contributors to the sound of the LA-610. Unlike other compressors which allow the user to adjust these parameters, the attack and release of the LA-610 are completely determined by the T4. There are several important characteristics of the T4 which play crucial roles in the sound of the LA-610. The first is the attack. The LA-2A was the first electro-optical compressor to use an electro-luminescent panel for the light source. Previous attempts at electro-optical compression employed either neon or incandescent lights. Both of these took time to light up, and this delay resulted in slow attacks. The electro-luminescent panel resulted in a faster attack than exhibited by other contemporary devices. The next important aspect is that of the release of the compressor. This is determined almost entirely by the characteristics of the photo-cell. The LA-610 the uses the same cadmium-sulfide photo-cells. The first important aspect of the cell is its �two-stage decay�. After the light is removed from the cell, it releases quickly (40-80 milliseconds) to approximately half of its off resistance. The remainder of its release can take place over as much as several seconds. The next aspect is the �memory� of the cell. This results in two important aspects of the character of the LA-610. The amount of time it takes for the cell to recover after the light is removed depends on how long light had been shining on it and how bright the light. In the case of the LA-610 this results in behavior where the release time is slower if the unit has either been in compression for a while, or the amount of compression is large. This signal dependent release characteristic is critical to the sound of the unit. The amount of compression, as well as the compression threshold, is controlled by the �Peak Reduction� potentiometer. This potentiometer controls the gain of the side-chain circuit. The greater the gain of this circuit, the lower the threshold and the greater the amount of
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