DSD over PCM - garbled playback

[Sagnasty]

Currently running rAudio 20241228

I attempted to play some DSF files (DSD256 and DSD128), but the output is choppy and unintelligible for each format. The DSF files in question are stored on my Synology DS718+ NAS with the network storage defined using NFS and connected via wired LAN.

I can successfully play these same DSF files using VLC on windows and iPhone app without issue.

I tried playing on Raspberry Pi 3B+ Rev 1.3 and Raspberry Pi 3B Rev 1.2 machines (HiFiBerry DAC+ Pro) with similar playback results.

FWIW - No playback issues with hi-res FLAC (I tested up to 24Bit-192kHz).

Jim

3 x Raspberry Pi 3B+ Rev 1.3 > HiFiBerry DAC+ Pro
1 x Raspberry Pi 3B Rev 1.2 > HiFiBerry DAC+ Pro
Synology DS718+

[findnix]

Hello @Sagnasty

Without further information this sounds for me like a bandwidth issue.

DSD128 playback produces at least 5,6 Mbit/s plus transport overhead (smb, nfs, transport encryption etc).
Expect over 20 Mbit/s for DSD256.
Regardless the discussion of the sense of using DSD128 and higher for home audio with consumer equipment there are some questions:

• Is your Syno capable to hold the stream?
• Is the (W)LAN from Syno to RPi fast enough?
• Is the RPi3 fast enough to deliver this bandwidth to the GPIO?
• Capabilities of HiFiBerry DAC+ Pro?

Greetings from Austria
Ronald

[Sagnasty]

Hello,
Did some additional testing with my system using DSD. Long story short – the garbled playback is not an issue with rAudio, and is instead a bandwidth issue as @findnix suggested.

Additional info:

• My NAS and LAN are more than capable to sustain this type of network traffic (Gigabit).
• The HiFiBerry DAC+ Pro supports max 192kHz/24bit PCM with no native DSD support (must use DoP) according to HiFiBerry forum posts.
• I can play 24 bit / 192 kHz PCM files with no issue (FLAC).
• I tried playing a DSD64 file which resulted in a much better sound output (still with some glitches). I noticed that the sustained CPU load was very high and the MPD status window indicated the following errors “rAudioHome mpd[92890]: alsa_output: Decoder is too slow; playing silence to avoid xrun”. As expected, results were progressively worse using DSD128 and DSD512 files.

Conclusion: My use case (Raspberry Pi 3B+ Rev 1.3 with HiFiBerry DAC+ Pro via I2S) is not a good candidate to play DSD files.

Contributing factors include (but not limited to):

• Currently using I2S instead of USB.
• DSD over PCM (DoP) implementation repacks a 16bit DSD stream into 24bit PCM frames (requires additional system resources with no audible benefit).
• The Raspberry Pi 3B+ Rev 1.3 “Gigabit” LAN connection is capped at 300 Mbit/s as it uses the USB 2.0 interface (shared USB/Ethernet bus). Playing DSD files should work using a capable external USB DAC with native DSD support – but I have not tested it yet.

Pi 4 and 5 are better candidates:

• Have true Gigabit network speeds (much better for use with a NAS / DSD streaming)
• Elimination of the shared USB/Ethernet implementation of the Raspberry Pi 3B+ Rev 1.3.
• USB 3.0
• Faster CPU's

Jim

3 x Raspberry Pi 3B+ Rev 1.3 > HiFiBerry DAC+ Pro
1 x Raspberry Pi 3B Rev 1.2 > HiFiBerry DAC+ Pro
Synology DS718+