the penguin

Understanding the use of DSD files with MPD

DSD, although a very old and failed technology, is again one of the hottest trends in computer audio. Below you will find a quick guide for MPD (Music Player Daemon) that will cover most of your needs:

MPD and DSD with DoP

Assuming that your DAC supports the DoP protocol, the only you need to do is to add the following line in audio_output section of mpd.conf:

dop       "yes"

Below you can see an example of this section:

audio_output {
enabled         "yes"
type            "alsa"
name            "Aune S16"
device          "hw:1,0"
auto_resample   "no"
auto_channels   "no"
auto_format     "no"
dop             "yes"
}

Then you just need to restart MPD

systemctl restart mpd

To double-check that everything is ok, you can start listening to ex. a DSD 64 file, and test with the following command:

cat /proc/asound/card*/pcm*p/sub*/hw_params

The output is:

closed
access: RW_INTERLEAVED
format: S24_LE
subformat: STD
channels: 2
rate: 176400 (176400/1)
period_size: 22050
buffer_size: 88200

DoP uses PCM and this is the reason that the format is S24_LE and the sampling rate is 176400.

MPD and Native DSD

Native DSD is a little bit more complicated. IF the DAC supports DSD and if the Linux Kernel supports your DAC in Native DSD mode, the only thing you need to do is remove the DoP option from audio_output section of mpd.conf

Below you can see an example of this section:

audio_output {
enabled         "yes"
type            "alsa"
name            "DiyinHK 9018k2m"
device          "hw:1,0"
auto_resample   "no"
auto_channels   "no"
auto_format     "no"
}

If everything is OK, then you will see the following output if you run the test command while listening to a DSD 64 file:

cat /proc/asound/card*/pcm*p/sub*/hw_params

closed
access: RW_INTERLEAVED
format: DSD_U32_BE
subformat: STD
channels: 2
rate: 88200 (88200/1)
period_size: 11025
buffer_size: 44100

The format now has changed and it’s DSD_U32_BE and the sampling rate is 88200.

If your DAC does not support Native DSD (like my Aune S16 below) or if it supports but Linux Kernel isn’t, when you remove the DoP option, MPD converts DSD to PCM on the fly and the test command has an output similar to the one below:

access: RW_INTERLEAVED
format: S32_LE
subformat: STD
channels: 2
rate: 352800 (352800/1)
period_size: 32768
buffer_size: 131072

The format is PCM again (S32_LE) and the sampling rate is the maximum the receiver and DAC support, 352800.

In general, Native DSD support is limited, so if your DAC supports DoP, this is the best way to listen to your DSD files at the moment. DoP is an old and mature protocol and has no audible differences when compared to Native DSD.

If you want to have a look at Linux kernel code and see the supported Native DSD devices, you can follow the link below:

https://github.com/torvalds/linux/blob/master/sound/usb/quirks.c

Please note that every Linux distro uses a different version of Linux kernel. In addition, if you use an embedded board like Raspberry Pi, Odroid, Udoo, you usually don’t use the mainline kernel and in many cases the kernel version is very old.

MPD and SACD ISO support

Although MPD does not officially support SACD ISO files, thanks to an MPD fork this option became available for MPD users.

What you need to do is build this fork (or ask your distribution for this package). The source code can be found in this location:

https://sourceforge.net/projects/mpd.sacddecoder.p/

This fork is almost identical to MPD apart from the SACD code. You need to edit mpd.conf and put some additional stuff:

decoder {
plugin "sacdiso"
dstdec_threads "4"
edited_master "true"
lsbitfirst "false"
playable_area "stereo"
}


decoder {
plugin "dvdaiso"
no_downmixes "false"
no_short_tracks "false"
playable_area "multichannel"
tags_path "/var/lib/mpd/dvda_metabase"
tags_with_iso "true"
}

The first section is for SACD ISO and the second for DVD ISO (I have never tested DVD ISO to be honest). Please note that you will have to modify for your needs.

Please note again that if you are using this fork this means that you are not using the official MPD, so if you have a problem and you need help you should always mention this in forum posts, bug reports etc.

Notes and random thoughts

#linux audio #dsd #mpd