Different designs of analogue mixing desk have subtle sonic differences. Although (usually) designed to be as transparent as possible, there tend to be differences in frequency response, low-level distortion and inter-channel crosstalk. Even this has been distilled into plugin form, notably in the form of the Slate Virtual Console Collection.
Whilst this may not amount to much on one channel, combining these effects across multiple channels in a mix leads to noticeable audible differences.
Some argue that processing every channel in the same way – old school-style – helps make a mix gel more easily. Could this be part of the allure of hardware summing mixers?
So that leaves us with the question – what is analogue vibe? It could be adding something (harmonics), or taking something away (high frequencies) or even doing something in a less mathematically perfect way.
PSP’s Vintage Warmer plugin attempts to distill many of the traits of analogue-style processing into one neat package.
‘Analogue’ effects can even be achieved using simple EQ, as demonstrated by iZotope Ozone:
Ultimately, it’s a combination of all of these factors that makes individual signals, and entire mixes, sound more ‘analogue’. The application of these effects boils down to individual production aesthetics, but it’s worth remembering that these are all powerful tools to have in your armoury.