While usually paid, UAD often offers their native plugins (which do not require hardware) during special promotions. If you catch a UAD "Spark" promotion, this is the most accurate emulation of the LA-2A available. C. Black Rooster Audio - VLA-2A (Free Trial/Light Versions) Verdict: Excellent, if available in a free bundle.
If you're able to find a free Teletronix LA-2A download that works, here's how to get started: teletronix la2a free download work
The compression time constant changes based on the input signal. It handles peaks differently than a quick limiter, resulting in transparent gain reduction. While usually paid, UAD often offers their native