Thoughts on this? I have not heard this in my recordings.
https://youtu.be/y3431uljZ2k?si=I7I7qhsKK7TUo49s
Wow. There's more information in the comments, including how Sound Devices (mostly?) fixed this with a firmware update.
Now I'm going to have to dig into some of my F6 recordings and see if I can locate this issue.
What I don't understand is why the low-gain ADC is 30 dB noisier than the high-gain one. I would expect it to be the reverse.
From what I understood, the recorder engages the low-gain ADC when it detects a transient - and it does so before the signal gets strong enough that it has the chance to clip. This means that there's some amount of guessing involved, and it might engage the low-gain ADC for sudden sounds that end up not getting anywhere near clipping level. And it's precisely because it has engaged the low-gain ADC for a sound that was actually fairly quiet that the device needs to make up for it by amplifying the signal digitally, raising the noise floor of the recording. It isn't that the low-gain ADC is noisier than the high-gain one in absolute terms (you're right that this would make no sense): it's that the high-gain one has cleaner analogue gain than simply boosting the digital signal produced by the low-gain one by however much is necessary so that the levels remain consistent throughout the recording.
You might have noticed he was recording tiny sounds (they sounded like water dripping?), not a gunshot or a drum kit. I imagine that these artefacts wouldn't appear in a live music recording in any noticeable way.
Edit: actually, I paid a bit more attention this time, and I don't think it's supposed to detect transients? It just routes the signal based on the voltage the microphone produces. So the situations when the issue would happen are a little different, but the same principle still applies. Basically, say the high-gain ADC is a +30dB one. Any signal strong enough to clip with that amount of gain is automatically routed to the low-gain ADC. If it's a healthy signal, you won't hear any noise. But if it's JUST loud enough to cross the clipping threshold of the high-gain ADC (say, by 1dB), then clearly the low-gain ADC is going to need to be boosted digitally so that the levels are consistent with rest of the recording. You're not going to see an issue when the sound falls into the best operational range of each ADC. You get some noise when a sound is just loud enough that you can't use cleaner gain, but still quiet enough that the new noise floor is noticeable.
