different downsample types

gb-emu/src/main.rs

@@ -9,7 +9,7 @@ use cpal::{
 };
 use futures::executor;
 use gb_emu_lib::{
-    connect::{AudioOutput, EmulatorMessage, JoypadState, Renderer, RomFile},
+    connect::{AudioOutput, DownsampleType, EmulatorMessage, JoypadState, Renderer, RomFile},
     util::scale_buffer,
     EmulatorCore,
 };
@@ -115,6 +115,9 @@ fn main() {
     }
 }
 
+const FRAMES_TO_BUFFER: usize = 1;
+const DOWNSAMPLE_TYPE: DownsampleType = DownsampleType::ZeroOrderHold;
+
 fn create_audio_output() -> (AudioOutput, Stream) {
     let host = cpal::default_host();
 
@@ -132,7 +135,8 @@ fn create_audio_output() -> (AudioOutput, Stream) {
 
     let sample_rate = config.sample_rate().0;
 
-    let (output, mut rx) = AudioOutput::new_unfilled(sample_rate as f32, true, 1);
+    let (output, mut rx) =
+        AudioOutput::new_unfilled(sample_rate as f32, true, FRAMES_TO_BUFFER, DOWNSAMPLE_TYPE);
 
     let stream = device
         .build_output_stream(

gb-vst/src/lib.rs

@@ -1,7 +1,7 @@
 use async_ringbuf::AsyncHeapConsumer;
 use futures::executor;
 use gb_emu_lib::{
-    connect::{AudioOutput, EmulatorMessage, JoypadButtons, RomFile},
+    connect::{AudioOutput, DownsampleType, EmulatorMessage, JoypadButtons, RomFile},
     EmulatorCore,
 };
 use nih_plug::prelude::*;
@@ -34,6 +34,7 @@ type JoypadSender = Mutex<Option<Sender<(JoypadButtons, bool)>>>;
 
 const FRAMES_TO_BUFFER: usize = 1;
 const INCLUDE_BOOTROM: bool = false;
+const DOWNSAMPLE_TYPE: DownsampleType = DownsampleType::ZeroOrderHold;
 
 impl Plugin for GameboyEmu {
     const NAME: &'static str = "Gameboy";
@@ -128,16 +129,24 @@ impl Plugin for GameboyEmu {
         };
 
         if let Some(ref mut vars) = self.vars {
-            let (output, rx) =
-                AudioOutput::new_unfilled(buffer_config.sample_rate, false, FRAMES_TO_BUFFER);
+            let (output, rx) = AudioOutput::new_unfilled(
+                buffer_config.sample_rate,
+                false,
+                FRAMES_TO_BUFFER,
+                DOWNSAMPLE_TYPE,
+            );
 
             vars.emulator_core.replace_output(output);
             vars.rx = rx;
         } else {
             let (sender, receiver) = channel::<EmulatorMessage>();
 
-            let (output, rx) =
-                AudioOutput::new_unfilled(buffer_config.sample_rate, false, FRAMES_TO_BUFFER);
+            let (output, rx) = AudioOutput::new_unfilled(
+                buffer_config.sample_rate,
+                false,
+                FRAMES_TO_BUFFER,
+                DOWNSAMPLE_TYPE,
+            );
 
             let (renderer, frame_receiver, key_handler) = EmulatorRenderer::new();
 

lib/src/connect/mod.rs

@@ -8,6 +8,12 @@ pub enum EmulatorMessage {
     Stop,
 }
 
+#[derive(Clone, Copy)]
+pub enum DownsampleType {
+    Linear,
+    ZeroOrderHold,
+}
+
 pub enum RomFile {
     Path(String),
     Raw(Vec<u8>),
@@ -43,6 +49,7 @@ pub struct AudioOutput {
     pub sample_rate: f32,
     pub send_rb: AsyncHeapProducer<[f32; 2]>,
     pub wait_for_output: bool,
+    pub downsample_type: DownsampleType,
 }
 
 impl AudioOutput {
@@ -50,8 +57,14 @@ impl AudioOutput {
         sample_rate: f32,
         wait_for_output: bool,
         frames_to_buffer: usize,
+        downsample_type: DownsampleType,
     ) -> (Self, AsyncHeapConsumer<[f32; 2]>) {
-        let (mut output, rx) = Self::new_unfilled(sample_rate, wait_for_output, frames_to_buffer);
+        let (mut output, rx) = Self::new_unfilled(
+            sample_rate,
+            wait_for_output,
+            frames_to_buffer,
+            downsample_type,
+        );
 
         executor::block_on(
             output
@@ -67,6 +80,7 @@ impl AudioOutput {
         sample_rate: f32,
         wait_for_output: bool,
         frames_to_buffer: usize,
+        downsample_type: DownsampleType,
     ) -> (Self, AsyncHeapConsumer<[f32; 2]>) {
         let rb_len = (sample_rate as usize / 60) * frames_to_buffer;
 
@@ -78,6 +92,7 @@ impl AudioOutput {
                 sample_rate,
                 send_rb,
                 wait_for_output,
+                downsample_type,
             },
             rx,
         )

lib/src/processor/memory/mmio/apu.rs

@@ -59,13 +59,13 @@ impl Apu {
             div_apu: 0,
             buffer: vec![],
             out_buffer: vec![],
-            converter: Downsampler::new(output.sample_rate),
+            converter: Downsampler::new(output.sample_rate, output.downsample_type),
             output,
         }
     }
 
     pub fn replace_output(&mut self, new: AudioOutput) {
-        self.converter = Downsampler::new(new.sample_rate);
+        self.converter = Downsampler::new(new.sample_rate, new.downsample_type);
         self.output = new;
     }
 

lib/src/processor/memory/mmio/apu/downsampler.rs

@@ -1,4 +1,4 @@
-use crate::constants::CLOCK_SPEED;
+use crate::{connect::DownsampleType, constants::CLOCK_SPEED};
 
 const TIME_PER_CYCLE: f32 = 1. / CLOCK_SPEED as f32;
 
@@ -42,15 +42,18 @@ impl Averager {
 pub(super) struct Downsampler {
     ratio: f32,
     time_accum: f32,
-    average: Averager,
+    average: Option<Averager>,
 }
 
 impl Downsampler {
-    pub fn new(sample_rate: f32) -> Self {
+    pub fn new(sample_rate: f32, algo: DownsampleType) -> Self {
         Self {
             ratio: 1. / sample_rate,
             time_accum: 0.,
-            average: Averager::default(),
+            average: match algo {
+                DownsampleType::Linear => Some(Averager::default()),
+                DownsampleType::ZeroOrderHold => None,
+            },
         }
     }
 
@@ -58,10 +61,16 @@ impl Downsampler {
         let mut output = vec![];
         for ref val in signal {
             self.time_accum += TIME_PER_CYCLE;
-            self.average.push(val);
+            if let Some(ref mut averager) = self.average {
+                averager.push(val);
+            }
             if self.time_accum >= self.ratio {
                 self.time_accum = 0.;
-                output.push(self.average.finish());
+                output.push(if let Some(ref mut averager) = self.average {
+                    averager.finish()
+                } else {
+                    *val
+                });
             }
         }
         output