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fix: remove DC offset from audio output

This commit is contained in:
Rekai Nyangadzayi Musuka 2022-10-21 05:12:45 -03:00
parent 55dada243e
commit 9d839a0328
2 changed files with 9 additions and 3 deletions
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5
src/apu.zig
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@ -200,7 +200,10 @@ pub const Apu = struct {
self.stream = SDL.SDL_NewAudioStream(SDL.AUDIO_U16, 2, @intCast(c_int, self.sampleRate()), SDL.AUDIO_U16, 2, host_sample_rate) orelse unreachable; self.stream = SDL.SDL_NewAudioStream(SDL.AUDIO_U16, 2, @intCast(c_int, self.sampleRate()), SDL.AUDIO_U16, 2, host_sample_rate) orelse unreachable;
} }
_ = SDL.SDL_AudioStreamPut(self.stream, &[2]u16{ final_left, final_right }, 2 * @sizeOf(u16)); // If we add 0x4040 to each sample the DC Offset is removed
// note: found this through guess and check
// FIXME: Pretty sure this is a dirty hack and should be fixed
_ = SDL.SDL_AudioStreamPut(self.stream, &[2]u16{ final_left + 0x4040, final_right + 0x4040 }, 2 * @sizeOf(u16));
self.sched.push(.SampleAudio, self.sampleTicks() -| late); self.sched.push(.SampleAudio, self.sampleTicks() -| late);
} }

7
src/main.zig
View File

@ -239,10 +239,13 @@ fn initAudio(apu: *Apu) SDL.SDL_AudioDeviceID {
return dev; return dev;
} }
// FIXME: Sometimes, we hear garbage upon program start. Why?
export fn audioCallback(userdata: ?*anyopaque, stream: [*c]u8, len: c_int) void { export fn audioCallback(userdata: ?*anyopaque, stream: [*c]u8, len: c_int) void {
const apu = @ptrCast(*Apu, @alignCast(8, userdata)); const apu = @ptrCast(*Apu, @alignCast(8, userdata));
_ = SDL.SDL_AudioStreamGet(apu.stream, stream, len); const written = SDL.SDL_AudioStreamGet(apu.stream, stream, len);
// If we don't write anything, play silence otherwise garbage will be played
// FIXME: I don't think this hack to remove DC Offset is acceptable :thinking:
if (written == 0) std.mem.set(u8, stream[0..@intCast(usize, len)], 0x80);
} }
fn getSavePath(alloc: std.mem.Allocator) !?[]const u8 { fn getSavePath(alloc: std.mem.Allocator) !?[]const u8 {