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The Urei LA-4 is a classic opto limiter that is useful on various instruments, such as vocals, guitar and bass. It has a unique sounding compression, with ratios selectable from 2:1,4:1, 8:1,12:1, 20:1. Anything above 8:1 is considered limiting. It also has variable threshold and output level. The LA-4 is primarily a single channel unit, with the option of stereo operation when linked to another unit. They do not have attack or release controls: the attack and release are nonlinear and are determined by the gain reduction. As such, the LA-4 is rather smooth sounding over a broad dynamic range. The LA-4 is great on vocals, giving a nice clarity and smooth compression that tames most erratic vocals. With a pair of LA-4s strapped for stereo operation, you can run compression on a stereo channel of background vocals. However, compared to its opto sibling, the LA-2A, the LA-4 have less warmth and presence. Hence, for to fatten a lead vocal, the LA-4 would not be the first choice of compressor when put up against the LA-2A (which we also have here in Digital Bear Entertainment). With that being said, LA-4s are perfect for background vocals that benefit more from sheen than from weight.
On bass, the LA-4 also has a rather smooth operation and compression. The non-linear attack and release ensure that the compression is not overly harsh or unnatural. The LA-4 also maintains the low frequency information from the bass track unlike other compressors that may lose low end information and make low register instruments overly crunchy on the high end.
The LA-4 is useful gear and a great addition to any studio. Compared to its other counterparts such as LA-2A and LA-3A, it is certainly the “blacksheep” of the family, with it being less present. However, it is definitely useful when you need a smooth and natural sounding compression.