shhh: an app that shushes.

Sometimes you are living near other people (who are not night owls) and you have your headphones on, and you don’t realize how loud you are.

So I wrote shhh: a small Rust daemon that watches the microphone level and literally says SHHH! when you are too loud.

Measuring loudness

This part was very interesting.

Decibels (dB) are a logarithmic unit. This is because you hear loudness roughly on a logarithmic scale. 3 dB louder is literally 2x the energy. So 9 dB is physically twice as energetic as 6 dB. However, your ear-brain system “does the math” and instead has a very strongly non-linear perception of loudness.

“Being loud” is harder to define and capture than most would think. Mics hear something different from you (e.g. bumping the table can be existential for the mic, but quiet to you). Raw samples are wayyyy too spiky to alert on. You’d get a constant shush response.

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 familiar units:

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

Always on

I put shhh in my .xsessionrc so it starts at login. Done.