Commits on Feb 25, 2023

1. dsound: don't restrict the host buffer to 16-bit …

   Currently, the DirectSound Host API code only creates 16-bit integer
   DirectSound buffers. All audio data provided by the user is therefore
   converted by PortAudio to and from 16-bit, regardless of the user buffer
   format.
   
   This basically makes it impossible to pass 24-bit audio through the
   DirectSound Host API.
   
   If the user buffer format is not 16-bit, this also causes pointless
   conversions to take place, *even if the hardware is running at 16-bit*,
   because modern Windows versions (Vista+) convert the data to floating
   point behind the scenes before it is handed off to the hardware. This
   can lead to silly situations where 32-bit float samples from the user
   are (lossily) converted to 16-bit by PortAudio, then ended off to
   Windows via DirectSound, only to be converted back to 32-bit float
   again, before finally being converted to the format the hardware device
   is configured to use. This can easily lead to two layers of
   16-bit dithering (one from PortAudio, and one from Windows) being piled
   on top of each other, resulting in an elevated noise floor.
   
   This commit fixes this problem by configuring the DirectSound buffers to
   use the same format as the user buffer. This should stop PortAudio from
   converting samples in all cases except paInt8, which is not supported by
   WAVEFORMATEX (only paUInt8 is).
   
   The new code assumes that DirectSound will accept whatever format we
   throw at it. I feel confident that this is always true on Vista+
   regardless of hardware, because starting from Vista DirectSound does not
   access hardware directly - it always goes through the Windows Audio
   Engine which supports all formats in both directions (I verified this
   using paloopback).
   
   The consequences of this change on pre-Vista Windows are less clear,
   although [1] suggests that this might just work even on 2000/XP as
   KMixer should be able to handle these conversions as well.
   
   [1]: https://microsoft.public.win32.programmer.directx.audio.narkive.com/elgNlPIn/
   
   Fixes PortAudio#54

   

   dechamps committed Feb 25, 2023
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