I’ve done that with a custom trigger tone before, and the trick is to pick a frequency that your mic actually likes, not just something your brain catches. Most large‑format condenser mics have a sweet spot around 5kHz to 7kHz, but that’s only when you’re looking for that airy, punchy top end. If you want something subtle, go for a low‑end pulse—say a 200Hz sine that you set at a mic’s low‑frequency response curve. Keep it under -60dB so it’s almost invisible in the mix, but your brain will still register the cue. The best way to nail it is to run a reference tone through a real mic in your listening space, record it, and measure the frequency response. Then tweak the tone generator to match the mic’s peak. That way the cue feels like a natural extension of the room rather than a jarring alarm. If you’re feeling fancy, add a slight 1/12th of a tone shift—like 200Hz plus 3.5 cents—to make it feel a bit unique; the brain loves that micro‑variation. Just remember, you’re not telling the mic to “get ready,” you’re letting the mic shape the sound, so keep the tone clean and let the mic’s physics do the heavy lifting.