Remove obsolete PPM helper functions

src/audio.rs

@@ -878,21 +878,6 @@ fn loudness_from_power(p: f32) -> f32 {
     -0.691 + 10.0 * p.max(1e-20).log10()
 }
 
-#[cfg(target_os = "linux")]
-fn db_per_s_to_tau(db_per_s: f32) -> f32 {
-    if db_per_s > 0.0 {
-        (20.0 / std::f32::consts::LN_10) / db_per_s
-    } else {
-        0.75
-    }
-}
-
-#[cfg(target_os = "linux")]
-fn make_release_coeff(sample_rate: u32, tau: f32) -> f32 {
-    let tt = tau.max(1e-5);
-    (-1.0 / (sample_rate.max(8_000) as f32 * tt)).exp()
-}
-
 #[cfg(target_os = "linux")]
 fn clamp_box_db(v: f32) -> f32 {
     v.clamp(BOX_MIN_DB, BOX_MAX_DB)