Although this particular trick isn't possible, it is desirable and sometimes you can mimic such features which seem impossible. I remember at around the turn o

Although this particular trick isn't possible, it is desirable and sometimes you can mimic such features which seem impossible. I remember at around the turn of the century a friend showed me a neat trick many Sony MD recorders could do, which I think has since been incorporated into many (but IMO never enough) digital recorders: Time machine. The compression needed for an MD recorder means a PCM buffer is needed, if we run the buffer all the time (after all it's just electronics) some engineer realised that this means you could choose to record audio that happened (and thus was in the buffer) before you actually decided to record it. When one of the band members drops an instrument & it makes the coolest noise you've ever heard, you have long enough to think "Fuck that sounded so cool" and reach across and hit record and still capture the sound.