shhh: a Rust program that tells me to be quiet

Apparently I get loud on calls when I’m excited. I found this out the way everyone does — someone told me, months too late. So I wrote shhh: a small Rust daemon that watches the microphone level and alerts me when I cross a threshold.

Measuring loudness

Raw sample amplitude is too twitchy to alert on. shhh computes RMS over a sliding window instead:

fn rms(samples: &[f32]) -> f32 {
    let sum_sq: f32 = samples.iter().map(|s| s * s).sum();
    (sum_sq / samples.len() as f32).sqrt()
}

…then converts to dBFS so the threshold is in units that mean something:

let db = 20.0 * rms.max(1e-9).log10();
if db > args.threshold {
    notify("shhh", "you're doing it again");
}

Audio capture is cpal, which was the easy part. The fiddly part was debouncing: a single laugh shouldn’t fire the alert, but thirty seconds of escalating enthusiasm should. The rule that stuck: alert only if the rolling average stays hot for a few seconds, then go quiet for a cooldown period so it doesn’t nag.

Does it work

Yes, annoyingly well. The notification pops via dunst in the corner of my xmonad setup, styled like everything else on the desktop. It has genuinely changed my call behavior, in the way that a graph of your own bad habit always does.

It’s a ~300 line program. Sometimes the fix for a human problem is a very small robot with one opinion.