diff options
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/user.xml | 177 |
1 files changed, 173 insertions, 4 deletions
diff --git a/doc/user.xml b/doc/user.xml index 3d6311dc8..b13689163 100644 --- a/doc/user.xml +++ b/doc/user.xml @@ -680,7 +680,7 @@ systemctl start mpd.socket</programlisting> <section id="config_audio_format"> <title>Audio Format Settings</title> - <section> + <section id="config_global_audio_format"> <title>Global Audio Format</title> <para> @@ -1143,6 +1143,175 @@ systemctl start mpd.socket</programlisting> </section> </chapter> + <chapter id="advanced_usage"> + <title>Advanced usage</title> + + <section id="bit_perfect"> + <title>Bit-perfect playback</title> + + <para> + "Bit-perfect playback" is a phrase used by audiophiles to + describe a setup that plays back digital music as-is, without + applying any modifications such as resampling, format + conversion or software volume. Naturally, this implies a + lossless codec. + </para> + + <para> + By default, <application>MPD</application> attempts to do + bit-perfect playback, unless you tell it not to. Precondition + is a sound chip that supports the audio format of your music + files. If the audio format is not supported, + <application>MPD</application> attempts to fall back to the + nearest supported audio format, trying to lose as little + quality as possible. + </para> + + <para> + To verify if <application>MPD</application> converts the audio + format, enable verbose logging, and watch for these lines: + </para> + + <programlisting>decoder: audio_format=44100:24:2, seekable=true +output: opened plugin=alsa name="An ALSA output" audio_format=44100:16:2 +output: converting from 44100:24:2</programlisting> + + <para> + This example shows that a 24 bit file is being played, but the + sond chip cannot play 24 bit. It falls back to 16 bit, + discarding 8 bit. + </para> + + <para> + However, this does not yet prove bit-perfect playback; + <application>ALSA</application> may be fooling + <application>MPD</application> that the audio format is + supported. To verify the format really being sent to the + physical sound chip, try: + </para> + + <programlisting>cat /proc/asound/card*/pcm*p/sub*/hw_params +access: RW_INTERLEAVED +format: S16_LE +subformat: STD +channels: 2 +rate: 44100 (44100/1) +period_size: 4096 +buffer_size: 16384</programlisting> + + <para> + Obey the "format" row, which indicates that the current + playback format is 16 bit (signed 16 bit integer, little + endian). + </para> + + <para> + Check list for bit-perfect playback: + </para> + + <itemizedlist> + <listitem> + <para> + Use the <link linkend="alsa_output">ALSA</link> output + plugin. + </para> + </listitem> + + <listitem> + <para> + Disable sound processing inside + <application>ALSA</application> by configuring a + "hardware" device (<parameter>hw:0,0</parameter> or + similar). + </para> + </listitem> + + <listitem> + <para> + Don't use software volume (setting <link + linkend="config_audio_outputs"><varname>mixer_type</varname></link>). + </para> + </listitem> + + <listitem> + <para> + Don't force <application>MPD</application> to use a + specific audio format (settings <link + linkend="config_audio_outputs"><varname>format</varname></link>, + <link + linkend="config_global_audio_format"><varname>audio_output_format</varname></link>). + </para> + </listitem> + + <listitem> + <para> + Verify that you are really doing bit-perfect playback + using <application>MPD</application>'s verbose log and + <filename>/proc/asound/card*/pcm*p/sub*/hw_params</filename>. + Some DACs can also indicate the audio format. + </para> + </listitem> + </itemizedlist> + </section> + + <section id="dsd"> + <title>Direct Stream Digital (DSD)</title> + + <para> + DSD (<ulink + url="https://en.wikipedia.org/wiki/Direct_Stream_Digital">Direct + Stream Digital</ulink>) is a digital format that stores audio + as a sequence of single-bit values at a very high sampling + rate. + </para> + + <para> + <application>MPD</application> understands the file formats + <link linkend="dsdiff_decoder"><filename>dff</filename></link> + and <link + linkend="dsf_decoder"><filename>dsf</filename></link>. There + are three ways to play back DSD: + </para> + + <itemizedlist> + <listitem> + <para> + Native DSD playback. Requires + <application>ALSA</application> 1.0.27.1 or later, a sound + driver/chip that supports DSD and of course a DAC that + supports DSD. + </para> + </listitem> + + <listitem> + <para> + DoP (DSD over PCM) playback. This wraps DSD inside fake + 24 bit PCM according to the <ulink + url="http://dsd-guide.com/dop-open-standard">DoP + standard</ulink>. Requires a DAC that supports DSD. No + support from ALSA and the sound chip required (except for + 24 bit PCM support). + </para> + </listitem> + + <listitem> + <para> + Convert DSD to PCM on-the-fly. + </para> + </listitem> + </itemizedlist> + + <para> + Native DSD playback is used automatically if available. DoP + is only used if enabled explicitly using the <link + linkend="alsa_output"><varname>dop</varname></link> option, + because there is no way for <application>MPD</application> to + find out whether the DAC supports it. DSD to PCM conversion + is the fallback if DSD cannot be used directly. + </para> + </section> + </chapter> + <chapter id="plugin_reference"> <title>Plugin reference</title> @@ -1527,7 +1696,7 @@ systemctl start mpd.socket</programlisting> <section id="decoder_plugins"> <title>Decoder plugins</title> - <section> + <section id="dsdiff_decoder"> <title><varname>dsdiff</varname></title> <para> @@ -1558,7 +1727,7 @@ systemctl start mpd.socket</programlisting> </informaltable> </section> - <section> + <section id="dsf_decoder"> <title><varname>dsf</varname></title> <para> @@ -2041,7 +2210,7 @@ systemctl start mpd.socket</programlisting> If set to <parameter>yes</parameter>, then DSD over PCM according to the <ulink url="http://dsd-guide.com/dop-open-standard">DoP - standard others</ulink> is enabled. This wraps DSD + standard</ulink> is enabled. This wraps DSD samples in fake 24 bit PCM, and is understood by some DSD capable products, but may be harmful to other hardware. Therefore, the default is |