I was checking the tuning of some audio using Lingot - via pipwire, connected within helvum. I noticed that when playback is stopped it’s sitting at F#6 which is weird.
After looking around my project for what could be causing it I tried disabling the one instance of x42 EQ that I’m using and that solved it. But why is the plugin causing this?
The plugin internally processes in steps of 32 samples, at 48kHz / 32 = 1.5kHz.
To prevent denormals, a tiny number (10^-10, equivalent to -200dBFS) is added to the input. So there is in fact a 1.5kHz signal, just below 32bit (-192dBFS), and usually lower since it is filtered.
The interesting part here however is that lingot shows it as -20dB signal. That should be audible. Can you hear it?
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PS. you can check with bitmeter (from x42-plugins):
No it’s not audible. But Lingot’s scale doesn’t make sense to me because it has 0, 20, 40, so if the 1.5kHz signal is at -20 that means every other frequency is at 0…
Edit: I just saw the tooltip in Lingot, it shows the signal to noise ratio.
Ah ok. S/N makes sense.
Interesting that lingo is that sensitive, and has no lower signal limit. It’s well below the thermal noise floor.
Adding a tiny number to prevent subnormals is a common practice, especially in reverbs, where the reverb tail might run into that range and cause increased CPU load. Ardour also has this feature built-in (context menu of each mixer channel-strip). Though modern CPU have features to disable subnormal processing.