Improve sample rounding and clean up noise shaping leftovers (#771)

Cargo.lock

@@ -435,6 +435,12 @@ dependencies = [
  "percent-encoding",
 ]
 
+[[package]]
+name = "fuchsia-cprng"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a06f77d526c1a601b7c4cdd98f54b5eaabffc14d5f2f0296febdc7f357c6d3ba"
+
 [[package]]
 name = "futures"
 version = "0.3.15"
@@ -1073,6 +1079,15 @@ version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c7d73b3f436185384286bd8098d17ec07c9a7d2388a6599f824d8502b529702a"
 
+[[package]]
+name = "libmath"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dfd3416934a853ae80d5c3b006f632dfcbaf320300c5167e88a469e9ac214502"
+dependencies = [
+ "rand 0.3.23",
+]
+
 [[package]]
 name = "libmdns"
 version = "0.6.1"
@@ -1085,7 +1100,7 @@ dependencies = [
  "if-addrs",
  "log",
  "multimap",
- "rand",
+ "rand 0.8.3",
  "socket2",
  "thiserror",
  "tokio",
@@ -1190,7 +1205,7 @@ dependencies = [
  "librespot-protocol",
  "log",
  "protobuf",
- "rand",
+ "rand 0.8.3",
  "serde",
  "serde_json",
  "tokio",
@@ -1223,7 +1238,7 @@ dependencies = [
  "pbkdf2",
  "priority-queue",
  "protobuf",
- "rand",
+ "rand 0.8.3",
  "serde",
  "serde_json",
  "sha-1",
@@ -1254,7 +1269,7 @@ dependencies = [
  "libmdns",
  "librespot-core",
  "log",
- "rand",
+ "rand 0.8.3",
  "serde_json",
  "sha-1",
  "simple_logger",
@@ -1288,6 +1303,7 @@ dependencies = [
  "gstreamer-app",
  "jack 0.7.1",
  "lewton",
+ "libmath",
  "libpulse-binding",
  "libpulse-simple-binding",
  "librespot-audio",
@@ -1296,7 +1312,7 @@ dependencies = [
  "log",
  "ogg",
  "portaudio-rs",
- "rand",
+ "rand 0.8.3",
  "rand_distr",
  "rodio",
  "sdl2",
@@ -1488,7 +1504,7 @@ dependencies = [
  "autocfg",
  "num-integer",
  "num-traits",
- "rand",
+ "rand 0.8.3",
 ]
 
 [[package]]
@@ -1840,6 +1856,29 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "rand"
+version = "0.3.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "64ac302d8f83c0c1974bf758f6b041c6c8ada916fbb44a609158ca8b064cc76c"
+dependencies = [
+ "libc",
+ "rand 0.4.6",
+]
+
+[[package]]
+name = "rand"
+version = "0.4.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "552840b97013b1a26992c11eac34bdd778e464601a4c2054b5f0bff7c6761293"
+dependencies = [
+ "fuchsia-cprng",
+ "libc",
+ "rand_core 0.3.1",
+ "rdrand",
+ "winapi",
+]
+
 [[package]]
 name = "rand"
 version = "0.8.3"
@@ -1848,7 +1887,7 @@ checksum = "0ef9e7e66b4468674bfcb0c81af8b7fa0bb154fa9f28eb840da5c447baeb8d7e"
 dependencies = [
  "libc",
  "rand_chacha",
- "rand_core",
+ "rand_core 0.6.2",
  "rand_hc",
 ]
 
@@ -1859,9 +1898,24 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e12735cf05c9e10bf21534da50a147b924d555dc7a547c42e6bb2d5b6017ae0d"
 dependencies = [
  "ppv-lite86",
- "rand_core",
+ "rand_core 0.6.2",
 ]
 
+[[package]]
+name = "rand_core"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a6fdeb83b075e8266dcc8762c22776f6877a63111121f5f8c7411e5be7eed4b"
+dependencies = [
+ "rand_core 0.4.2",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9c33a3c44ca05fa6f1807d8e6743f3824e8509beca625669633be0acbdf509dc"
+
 [[package]]
 name = "rand_core"
 version = "0.6.2"
@@ -1878,7 +1932,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "da9e8f32ad24fb80d07d2323a9a2ce8b30d68a62b8cb4df88119ff49a698f038"
 dependencies = [
  "num-traits",
- "rand",
+ "rand 0.8.3",
 ]
 
 [[package]]
@@ -1887,7 +1941,16 @@ version = "0.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3190ef7066a446f2e7f42e239d161e905420ccab01eb967c9eb27d21b2322a73"
 dependencies = [
- "rand_core",
+ "rand_core 0.6.2",
+]
+
+[[package]]
+name = "rdrand"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "678054eb77286b51581ba43620cc911abf02758c91f93f479767aed0f90458b2"
+dependencies = [
+ "rand_core 0.3.1",
 ]
 
 [[package]]
@@ -2212,7 +2275,7 @@ checksum = "dac1c663cfc93810f88aed9b8941d48cabf856a1b111c29a40439018d870eb22"
 dependencies = [
  "cfg-if 1.0.0",
  "libc",
- "rand",
+ "rand 0.8.3",
  "redox_syscall",
  "remove_dir_all",
  "winapi",

playback/Cargo.toml

@@ -20,6 +20,7 @@ version = "0.2.0"
 [dependencies]
 futures-executor = "0.3"
 futures-util = { version = "0.3", default_features = false, features = ["alloc"] }
+libmath = "0.2"
 log = "0.4"
 byteorder = "1.4"
 shell-words = "1.0.0"

playback/src/convert.rs

@@ -32,18 +32,19 @@ impl Converter {
 
     // Denormalize and dither
     pub fn scale(&mut self, sample: f32, factor: i64) -> f32 {
+        let dither = match self.ditherer {
+            Some(ref mut d) => d.noise(),
+            None => 0.0,
+        };
+
         // From the many float to int conversion methods available, match what
         // the reference Vorbis implementation uses: sample * 32768 (for 16 bit)
-        let int_value = sample * factor as f32;
+        let int_value = sample * factor as f32 + dither;
 
-        // https://doc.rust-lang.org/nomicon/casts.html: casting float to integer
+        // Casting float to integer rounds towards zero by default, i.e. it
-        // rounds towards zero, then saturates. Ideally halves should round to even to
+        // truncates, and that generates larger error than rounding to nearest.
-        // prevent any bias, but since it is extremely unlikely that a float has
+        // Absolute lowest error is gained from rounding ties to even.
-        // *exactly* .5 as fraction, this should be more than precise enough.
+        math::round::half_to_even(int_value.into(), 0) as f32
-        match self.ditherer {
-            Some(ref mut d) => int_value + d.noise(int_value),
-            None => int_value,
-        }
     }
 
     // Special case for samples packed in a word of greater bit depth (e.g.

playback/src/dither.rs

@@ -32,7 +32,7 @@ pub trait Ditherer {
     where
         Self: Sized;
     fn name(&self) -> &'static str;
-    fn noise(&mut self, sample: f32) -> f32;
+    fn noise(&mut self) -> f32;
 }
 
 impl fmt::Display for dyn Ditherer {
@@ -64,7 +64,7 @@ impl Ditherer for TriangularDitherer {
         "Triangular"
     }
 
-    fn noise(&mut self, _sample: f32) -> f32 {
+    fn noise(&mut self) -> f32 {
         self.distribution.sample(&mut self.cached_rng)
     }
 }
@@ -87,7 +87,7 @@ impl Ditherer for GaussianDitherer {
         "Gaussian"
     }
 
-    fn noise(&mut self, _sample: f32) -> f32 {
+    fn noise(&mut self) -> f32 {
         self.distribution.sample(&mut self.cached_rng)
     }
 }
@@ -113,7 +113,7 @@ impl Ditherer for HighPassDitherer {
         "Triangular, High Passed"
     }
 
-    fn noise(&mut self, _sample: f32) -> f32 {
+    fn noise(&mut self) -> f32 {
         let new_noise = self.distribution.sample(&mut self.cached_rng);
         let high_passed_noise = new_noise - self.previous_noises[self.active_channel];
         self.previous_noises[self.active_channel] = new_noise;