tweak pipeline buffers rather than i2s dma buffer

this maintains the bluetooth changes to buffer sizes, but keeps the most
important i2s buffer the same size

src/audio/audio_converter.cpp

@@ -25,7 +25,7 @@
 [[maybe_unused]] static constexpr char kTag[] = "mixer";
 
 static constexpr std::size_t kSampleBufferLength =
-    drivers::kI2SBufferLengthFrames * sizeof(sample::Sample) * 2;
+    drivers::kI2SBufferLengthFrames * sizeof(sample::Sample);
 static constexpr std::size_t kSourceBufferLength = kSampleBufferLength * 2;
 
 namespace audio {

src/audio/audio_decoder.cpp

@@ -48,7 +48,7 @@ namespace audio {
 [[maybe_unused]] static const char* kTag = "audio_dec";
 
 static constexpr std::size_t kCodecBufferLength =
-    drivers::kI2SBufferLengthFrames * sizeof(sample::Sample) * 2;
+    drivers::kI2SBufferLengthFrames * sizeof(sample::Sample);
 
 Timer::Timer(std::shared_ptr<Track> t,
              const codecs::ICodec::OutputFormat& format)

src/drivers/include/i2s_dac.hpp

@@ -27,10 +27,12 @@
 
 namespace drivers {
 
-// We normalise to 2-channel, 16 bit audio, which gives us a max of 4092 / 2 / 2
-// (16 bits) frames. This in turn means that at 48kHz, we have about 10ms of
-// budget to fill each buffer.
-constexpr size_t kI2SBufferLengthFrames = 512;
+// DMA max buffer size for I2S is 4092. We normalise to 2-channel, 16 bit
+// audio, which gives us a max of 4092 / 2 / 2 (16 bits) frames. This in turn
+// means that at 48kHz, we have about 21ms of budget to fill each buffer.
+// We base this off of the maximum DMA size in order to minimise the amount of
+// work the CPU has to do to service the DMA callbacks.
+constexpr size_t kI2SBufferLengthFrames = 1024;
 
 /**
  * Interface for a DAC that receives PCM samples over I2S.