sound: change audio_latency meaning similar to what it was before (20ms steps for portaudio, xaudio2, wasapi), old mame.ini default setting of 2 should work fine

docs/man/mame.6

@@ -948,11 +948,11 @@ Sets the startup volume. It can later be changed with the user interface
 .\" +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 .TP
 .B \-audio_latency, \-alat \fIvalue
-This controls the amount of latency in seconds built into the audio streaming.
+This controls the amount of latency built into the audio streaming.
 Smaller values provide less audio delay while requiring better system
 performance.  Higher values increase audio delay but may help avoid
-buffer under-runs and audio interruptions.  The default is 0.0 and will pick
+buffer under-runs and audio interruptions.  The default is 0 and will
-a sane duration.
+pick a sane duration.
 .\"
 .\" *******************************************************
 .SS Input options

docs/source/commandline/commandline-all.rst

@@ -3065,22 +3065,23 @@ Core Sound Options
 
 **-audio_latency** *<value>* / **-alat** *<value>*
 
-    Audio latency in seconds, up to a maximum of 0.5 seconds.  Smaller values
+    Audio latency, conventionally in number of audio frames (1 audio frame is 20ms).
-    provide less audio delay while requiring better system performance.  Larger
+	It is not required to supply whole numbers, eg. a value of ``1.5`` is 30ms).
-    values increase audio delay but may help avoid buffer under-runs and audio
+    Smaller values provide less audio delay while requiring better system
-    interruptions.  A value of 0.0 will use the default for the selected sound
+	performance.  Larger values increase audio delay but may help avoid buffer
-    module.
+    under-runs and audio interruptions.  A value of ``0`` will use the default
+    for the selected sound module.
 
     You may need to change the value of this option if you change the sound module
     using the :ref:`sound option <mame-commandline-sound>`.  This option is
     unsupported on sound modules ``pipewire``, ``pulse``, ``sdl``.
 
-    The default is ``0.0``.
+    The default is ``0``.
 
     Example:
         .. code-block:: bash
 
-            mame galaga -audio_latency 0.1
+            mame galaga -audio_latency 2
 
 
 .. _mame-commandline-inputoptions:

src/osd/modules/lib/osdobj_common.cpp

@@ -144,7 +144,7 @@ const options_entry osd_options::s_option_entries[] =
 
 	{ nullptr,                                   nullptr,          core_options::option_type::HEADER,    "OSD SOUND OPTIONS" },
 	{ OSDOPTION_SOUND,                           OSDOPTVAL_AUTO,   core_options::option_type::STRING,    "sound output method: " },
-	{ OSDOPTION_AUDIO_LATENCY ";alat(0.0-0.5)",  "0.0",            core_options::option_type::FLOAT,     "audio latency in seconds, 0.0 for default (increase to reduce glitches, decrease for responsiveness)" },
+	{ OSDOPTION_AUDIO_LATENCY ";alat(0.0-50.0)", "0.0",            core_options::option_type::FLOAT,     "audio latency, 0 for default (increase to reduce glitches, decrease for responsiveness)" },
 
 #ifdef SDLMAME_MACOSX
 	{ nullptr,                                   nullptr,          core_options::option_type::HEADER,    "CoreAudio-SPECIFIC OPTIONS" },

src/osd/modules/sound/pa_sound.cpp

@@ -163,7 +163,7 @@ int sound_pa::init(osd_interface &osd, osd_options const &options)
 	m_info.m_default_source = dc(Pa_GetDefaultInputDevice());
 
 	m_stream_id = 1;
-	m_audio_latency = options.audio_latency();
+	m_audio_latency = options.audio_latency() / sound_manager::STREAMS_UPDATE_FREQUENCY;
 	m_machine = &downcast<osd_common_t &>(osd).machine();
 
 	return 0;

src/osd/modules/sound/wasapi_sound.cpp

@@ -6,6 +6,7 @@
 //
 //====================================================================
 
+#include "emu.h"
 #include "sound_module.h"
 
 #include "modules/osdmodule.h"
@@ -499,7 +500,7 @@ int sound_wasapi::init(osd_interface &osd, osd_options const &options)
 	HRESULT result;
 
 	// get relevant options
-	m_audio_latency = options.audio_latency();
+	m_audio_latency = options.audio_latency() / sound_manager::STREAMS_UPDATE_FREQUENCY;
 	if (m_audio_latency == 0.0F)
 		m_audio_latency = 0.03F;
 	m_audio_latency = std::clamp(m_audio_latency, 0.01F, 1.0F);

src/osd/modules/sound/xaudio2_sound.cpp

@@ -6,6 +6,7 @@
 //
 //====================================================================
 
+#include "emu.h"
 #include "sound_module.h"
 
 #include "modules/osdmodule.h"
@@ -387,7 +388,7 @@ int sound_xaudio2::init(osd_interface &osd, osd_options const &options)
 	}
 
 	// get relevant options
-	m_audio_latency = options.audio_latency();
+	m_audio_latency = options.audio_latency() / sound_manager::STREAMS_UPDATE_FREQUENCY;
 	if (m_audio_latency == 0.0F)
 		m_audio_latency = 0.03F;
 	m_audio_latency = std::clamp(m_audio_latency, 0.01F, 1.0F);