· I am using Roon Arc 1.81.424 (425) on iOS 26.7 on an iPhone 17 Pro Max connected to a Quloos MUB5 DAC/AMP.
I am using the latest production build of Roon Server/Core on a sonicTransporter i7.
In general everything works fine and I am happy with the results. When I switch to using Sample Rate Conversion set to a fixed rate of DSD256 (DoP), I think there is a clear improvement in the audio quality, which I am happy about. However, I often — but not always — encounter brief drop-outs in audio that may last about a second or I hear a terrible scratching/squelching sound (that reminds me of a needle scraping and jumping across a record).
I have experienced this with music streamed from Tidal or Qobuz or stored locally on my iphone. Maybe — not certain — it is more reliable when I switch the phone into airplane mode and limit myself to downloaded albums.
Is this a limitation you are aware of? Is there anything I can do to improve the reliability? It almost seems as though Arc has not buffered enough of the audio stream before handing on to the USB output.
Tell us about your home network
· Home network is all Unifi with ethernet backhauls for each wifi access point. Roon Server/Core is wired. The Arc remote access relevant for this issue is over every type of connection — in the home, over various VPNs, over 5G, from different countries, fiber networks, etc.
Thank you for your post and our apologies for the delay in responding.
There are no known limitations with ARC that would cause audible artifacts. If ARC encountered an error with buffering or transcoding, playback would tear down.
Can you please share a screenshot of the Signal Path under the configuration with which you’re experiencing these issues? This will be transparent to the actual digital chain as the vendor DAC firmware reports it to ARC. Any transcoding performed on Roon’s side will be displayed.
Please also list the name of a track that recently exhibited these issues. Do they occur at the same point in the track each time?
The issues — random brief gaps + distortions — happen with any album and any format. Streamed and/or downloaded.
I have attached three sample Source Paths, each reflecting a different source format. I also attached a photo of the screen of the MUB5 that confirms that it is receiving DSD256.
Interestingly, I noticed that when I take screenshots when listening with SRC to DSD256, I hear a screeching sound through my earphones. On the other hand, when listening to PCM — with or without SRC — the screenshot action is silent. Also, if I receive an incoming message that triggers a sound (WhatsApp, for example), it squawks, whereas with PCM the audi on temporarily reduces in volume. It sounds like DSD is not preserving the exclusive mode…
iOS doesn’t support the type of Exclusive Mode you’re describing, because Apple blackboxes the audio pathway. Everything goes through the system mixer (Android, under certain configurations, can bypass the system mixer). System notifications are mixed into the stream you’re upsampling on Apple phones, and DoP wraps DSD inside PCM frames. The top 8 bits of each sample are marker bytes (0x05/0xFA, alternating) that tell the DAC “this is DSD.” When iOS mixes in a system sound or ducks the volume, it changes the sample values. That breaks the markers. The result is audible artifacts in the stream.
The silences you hear are likely the phone falling behind the buffer with this scale of data transfer. Upsampling 44.1KHz or even 192KHz to DSD256 increases the total data transported by an order of magnitude. It’s likely that the server is sending these segments to the phone, but the phone isn’t receiving them quickly enough to pass over to the DAC.
If that was the case (iPhone not receiving the segments quickly enough), then the issue should not occur with locally stored albums, but it does.
Given your description of the apparent limitations of iOS, is there anything that can be done within ARC now or in future updates that can remedy the issues I am facing? for example:
Switching to airplane mode — even if that limits me to downloaded albums, loses artwork and lyrics.
Enabling one of the Do Not Disturb modes
Muting the phone
Future app updates
Etc
If not, I wonder what the use is of having the DSD options available (playback and SRC). I’m inquisitive, not trying to be challenging.
Two separate problems here, so let us take them apart.
The screech when a system sound plays. DoP carries DSD inside PCM frames, and the top byte of each sample is a marker that alternates between 0x05 and 0xFA to tell the DAC this is DSD. If iOS alters those samples, the markers stop being markers and the DAC plays them as audio. No app can take exclusive ownership of the audio path on iOS, so we cannot prevent this from Roon’s side.
What reduces it: the silent switch (this covers screenshot and notification sounds, so it is the one to try first), then a Focus mode, then airplane mode. None of these is a fix.
The one second dropouts. No answer yet, and your point stands: if the phone were not receiving data fast enough, local files would be unaffected. Please disregard that part of our earlier reply.
Three things would help:
Please confirm you are on Roon Server 2.73 or later and on the current Roon ARC build. The extra diagnostics we need for this only work on those, so please update both if you are behind.
Please set Sample Rate Conversion to DSD128 for a while. If the dropouts become rarer, this scales with the conversion load on the phone. If nothing changes, it points elsewhere.
Next time one happens, please note the date and time with your timezone, and whether it was a local file or streaming. Once you confirm the builds we will turn on the additional logging and collect that window.
On the DSD options. They exist mainly so DSD content reaches a DSD capable DAC without being converted down. Upsampling everything to DSD256 on a phone is the heaviest use of that path, and on iOS the least protected from interference, which is why the edges show there.
I think there are three distinct issues and not two.
Issue 1: The screech when a system sound plays.
I understand your explanation of this. I had already experimented with these options before. While (I believe) that it eliminated the system interruptions due to message alerts etc, it did not eliminate either Issue 2 or 3.
Issue 2: The one second dropouts.
While I am still traveling away from my server, I always have it updated promptly. It is on the latest version that was available as of 1 month ago, which I believe is 2.73. The Roon ARC build is 1.83.427 (build 427).
I will try setting the SRC to DSD128 to see if it makes any difference and will get back to you, along with notes on timing and the source of the file.
Issue 3: The scratching/squelching sound mid play that I cannot directly attribute to system sounds (happens event the silent switch is active and iPhone is set to Do Not Disturb)
Note that this is the worst offender both because it is disturbing to hear and also because it lasts a long time. Sometimes it recovers in a second or two, but often it is so disturbing that I quickly pause the music and wait a few seconds before resuming again. I will see if these instances are reduced with DSD128 as well and will report back.
Thanks for confirming the builds. We agree these are three separate problems: the screech from system sounds, the one second dropouts, and the scratching sound that happens even with the silent switch and Do Not Disturb on. We will treat the last two as separate from system sounds.
We have turned on diagnostic logging for Roon ARC on your account. Please restart Roon Server, then fully close and reopen Roon ARC on your phone. The logs only cover the time after that.
When it happens again, please open Roon ARC right away and reply here with the date and time (including your time zone), whether the track was local or streaming, and whether it was a dropout or the scratching sound. Please keep Roon ARC open on your phone while you reply, so we can retrieve the logs from our side. The sooner after it happens, the better, because the logs keep a limited window.
If you also have the time, please keep the DSD128 test going and let us know what you see there.
Note that I just returned from my trip and found that Roon Server was still on 2.71. I just updated it this morning to 2.73.
While this is not conclusive as the testing times have not been long enough to rule out intermittent behavior:
Before Oct 1, I was in remote location with sub-par internet. From this location, I frequently experienced all three types of issues that ai reported.
On Oct 1+, I was in a major European capital with high speed fiber. With my iPhone now always in silenced mode when using Arc, I only experienced the gaps in audio and not the other two issues. I believe that I experienced these gaps only with DSD256, but I also switched to DSD128 at your request and I may have experienced some gaps there — and am not certain. In any case, could worse internet connections be factors in the two other sounds?
In any case as I am back home as of today, I will follow your instructions and log any issues with either DSD256 or DSD128. Thank you.
Thanks for the update and for continuing the testing. We will keep an eye on the DSD256 and DSD128 results, and it will be useful to see whether the dropouts, scratching, or both still show up now that you are back home.
