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I've just found out about how to do stems when recording, and why they're important (kind of obvious, I guess!) The only thing I can't work out, is where "full-mix" reverb is applied. If I want a particular reverb for the whole mix, it needs to be on each of the stems which are then summed for the full mix, right? I have worked out that you can't use a single reverb, and send it back to the stems, as you'd end up with the reverb of all the tracks on all the stems. So presumably, you use identical reverbs for each stem, if you want the same effect as all the tracks having the same reverb.

But is this how multiple, identical reverbs work? If multiple tracks are sent to identical reverbs, and then summed, does this sound the same as sending all tracks to one reverb?

  • Most people probably use sends to an all-wet reverb bus and then export the output of that reverb bus as another stem. – Linuxios Oct 28 '16 at 22:45
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In theory, yes. A filter is known as linear if it is both additive and homogeneous. For an additive filter, the filtered sum of signals is the same as the sum of filtered signals. (Homogeneity means that gain or attenuation can come before or after the filter.) Most digital reverbs, including all convolution reverbs, are linear filters.

In practice, also yes, but some reverbs are nonlinear. Nonlinear digital reverbs are usually specially made that way, with indicators like "shimmer" (pitch shift) and "vintage" (bitcrush). Analog reverbs using springs and plates are also naturally nonlinear, some more than others. Other factors in the signal path, like intermediate clipping, can also forfeit the linearity property.

  • Brilliant - thanks for this. After a lot of Googling I suspected this was the case, but was keen to have a definitive answer. (I'll just see if anybody adds anything soon before accepting...) – Bob Broadley Oct 29 '16 at 12:19
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    an admission... If I have something like a shimmer-typer rev on a full mix, I deconstruct it to the stems & hope no-one notices. Even if the difference can be heard, the actual intent is still usually viable as a stem mix; really because if you are going to do your own re-mix of the stems there is no alternative but to have them separate. I have been known to submit stems & their ambience tracks separately, for projects where my intent is not necessarily the final production choice. – Tetsujin Oct 29 '16 at 17:06
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Print the stem only reverbs to an audio track, then print the full mix with reverb to an audio track, line the tracks up to start at the same time, solo them, and invert the phase on one of the tracks if you hear anything they are different.

  • Are you asking whether reverb applied to each stem is the same as reverb from the entire mix printed to one stem is equivalent? If so, an easy way to tell would be to sum all of the per stem reverb returns to one stereo track, then print the full mix reverb return to a stereo tracks, stack these atop one another, solo them flip the phase of one, and what you hear will be the difference, if you hear nothing they are identical. Physics. – 24tracks Mar 24 '17 at 19:47

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