UA’s Unison plug‑ins don’t just model analogue colour — they can also change the impedance of the preamp itself, which in turn can alter the response of some microphones while recording.
I’m curious about using UAD plug‑ins. Would there be a noticeable difference in recording directly and committing (printing) to a Unison plug‑in, versus recording the vocal dry and afterwards adding the preamp plug‑in as an insert? I saw a few comments mentioning impedance, but I don’t understand how that will dramatically affect the sonic quality/characteristics.
SOS Forum post
SOS Editor In Chief Sam Inglis replies: The answer is... it depends! The usual recommendation is that the input impedance of a preamp should be at least 10 times the output impedance of the mic. That way, the mic is not ‘loaded’ by the preamp and, in theory, you get the truest representation of the signal generated at the capsule. However, some older mics, such as Shure’s SM57, were designed to work into preamps with much lower input impedances, and they can sound different when they do — you could say that the designers ‘voiced’ them with that loading effect in mind.
Mics with electronically balanced output stages (in other words, most modern active mics) are pretty much immune from these loading effects, and will sound the same regardless of preamp impedance. Passive and transformer‑balanced mics, on the other hand, can sound different.
Some older mics, such as Shure’s SM57, were designed to work into preamps with much lower input impedances.
So, in theory, if you’re using a modern capacitor mic with an electronically balanced output stage, it should sound the same whether you record through the plug‑in in Unison mode, or record through a clean preamp and apply the plug‑in later. But if you’re using an older mic, there may be a difference.