Some plug‑ins might not behave in exactly the same way every time you play your track. In the case of PSP’s excellent Wobbler plug‑in, for example, the chosen Mode setting dictates whether or not the phase of the modulation will be reset so that it starts from the same point in its cycle each time you start playback.
I use Reaper, and to check that some clip effects were rendering properly, I bounced them and put them on a clean track. I matched the fader levels and flipped the polarity of the new track. I should hear nothing when both tracks play, right? But I don’t. Is it a problem with Reaper or is there something I’m missing? Thanks in advance for any insight!
Anonymous, via email
SOS Reviews Editor Matt Houghton replies: There are a few possible explanations here, but you don’t mention what plug‑ins you’re using — and the plug‑in is the most likely culprit. Two signals will only cancel completely when one is inverted if they are both identical. Yet lots of plug‑ins don’t do quite the same thing each time you play through your track. For example, if there’s modulation involved, the phase of that modulation won’t necessarily be linked to your DAW’s transport — in other words, the modulation may not trigger from the start of its cycle each time you hit Play. The effect might involve some randomisation element in the algorithm too. Similarly, a sample‑based instrument or drum trigger plug‑in might, by design, randomly play different samples to make it sound more realistic. In such cases, your rendered file won’t be identical to the plug‑in’s output next time you play the track — that could well explain why you’re not hearing silence.
You don’t mention what plug‑ins you’re using — and the plug‑in is the most likely culprit.
Another possibility is that there’s a level change or other process applied in the rendering signal path. For example, if your initial track is routed through a bus on which the gain or fader is at anything but unity and you print that level change when rendering, and the rendered track is routed through that same bus, then the level change is applied once to the live track, but twice to the rendered one. The same goes for any bus compression or EQ. Again, in either case, the two signals won’t null because they’re not identical.
If the changes are small, then one more avenue to explore is the resolution at which you’re rendering: if you export at a different sample rate or word length (‘bit depth’) than the project, and then re‑import to the project, that could cause small differences. However, since you mention “clip effects” I believe these are automatically rendered at the project settings — which is what leads me to suspect that it’s simply a matter of the plug‑in doing slightly different things each time you hit play. What matters most, of course, is whether things sound good when you bounce them. If they do, then there’s really no point looking for problems.