Faint clicks/pops during playback of 24/96, 24/192 PCM and DSD files

[rongon]

I have a RPi 3B+ in my bedroom, running moOde 9.2.1 with music files stored locally on a couple of 512GB USB thumb drives connected to the USB ports on the RPi itself. The DAC is a Topping D10, connected to a USB port on a powered USB hub. 

I hear faint clicks/pops during playback of higher resolution FLAC files (24/96 and 24/192) or DSD files (.dsf). 
I don't hear those noises while playing back 16/44.1 or 16/48 FLAC files.
I don't hear those noises while playing back 24/44.1 or 24/48 FLAC files. 

Any ideas on what might cause issues like that? 

I tried the same DAC I'm using with this RPi3B+ connected to my RPi4. It worked fine (no clicks/pops).
I also tried my other known-working DAC with this RPi3B+ and it too played back with pops/clicks on high sample rate files.
That makes me suspect that the issue is not caused by the DAC.

I'm not resampling (no SoX, etc.). No EQ (e.g., Camilla), no crossfeed, etc.

I find that the problem is a bit less severe if I keep the plastic RPi case open and let the CPU 'breathe'. I added better quality heatsinks to the ICs on the pcb, which did help a bit, but has not completely fixed the problem. Is it possible my old RPi 3B+ is overheating while processing those larger files? 

Can cache or buffer sizes cause this kind of problem? 
Any recommendations for settings? I set buffer sizes to defaults in MPD.  

The next thing I'll try is to move the USB thumb drives to the powered USB hub, in case it's a power supply current draw issue. That seems like a stretch, but at this point anything seems worth a try. 

Any suggestions for what else I should try? 

Thank you in advance for any suggestions you can send my way. 
--

[TheOldPresbyope]

Random thoughts:

1) Out of the box, the 4B is more powerful than the 3B+. It is faster and has more memory. That may explain the difference you see changing them.

2) With the 3B+, are you using the default "On demand" CPU governor setting (in m>config>system)? You might try the "Performance" setting. (Note: the CPU temp may go up as a result) This forces the CPU to run at full speed constantly rather than ramping down and up with demand.

3) Have you used the terminal command vcgencmd to look at the possibility that your 3B+ is thermal throttling? You can use your favorite Internet search engine to find out how to use this command to query system information fro the VideoCore.

Regards,
Kent

[Nutul]

I had a "similar" issue with my "old" 3B+, although I am/was in a slightly different situation:
1. I only have/had disc-rips + CUE
2. the clicks / pops were limited to some sort of struggle-to-sinc in the transition from one track to another (the next...) AND not always, resulting anyway in a sort of click...
So I fixed it increasing the cache size to 1GB (as my rips are 16/44.1, therefore usually in the 350/400 MB realm... so being sure to have the whole file in memory)
It could be an issue of horsepower, though, as @TheOldPresbyope pointed out, and you happen to have verified, as the Pi4 does not present the issue...
Anyway, since increasing the cache size (provided you DO have enough memory) does no harm and is a no-brainer, you can easily give it a try.

[roderickvd]

High-res PCM and DSD have pretty high bitrate, and the USB bus on the RPi3 is shared and could get congested going from USB stick to USB DAC.

[rongon]

Thank you everybody.

If the problem is data congestion along the USB bus, what measures could I take to improve things?
I could install my old Allo BOSS DAC HAT instead of the USB DAC. That would be a useful experiment, I guess.
The problem there is that the bedroom RPi must use a WiFi connection to my network, and installing the BOSS DAC HAT knocks out the RPi3B+ built-in WiFi adapter. I dug up a USB WiFi adapter that should work, but wouldn't that be a sideways move? Which device demands more data I/O throughput from the USB bus, a stereo DAC or an AC600 WiFi adapter?

I had the CPU governor set to On-Demand. I've set it to Performance. We'll see if that helps.

I fixed it increasing the cache size to 1GB

Which cache setting did you alter? 

Audio buffer ? 
Output buffer ? 
Input cache ? 

My RPi3B+ has 1GB of RAM.

The input cache on my RPi was set to 128MB (the default). I'll try increasing that to 512MB and see if that makes the clicks/pops go away.

[rongon]

According to RaspberryTips (https://raspberrytips.com/raspberry-pi-temperature/) I should only really worry if my RPi's CPU temperature gets up near 85C.

I had the RPi play an album's worth of DSD64 dsf files.
At idle, vcgencmd measure_temp returned 52.6C
After 5 mins of playback, vcgencmd measure_temp returned 53.7C
After 10 mins, it returned 54.8C
After 15 mins, it returned 54.2C

Then I had the RPi play an album of 24/192k PCM FLAC files.
After 5 mins of continuous playback, vcgencmd measure_temp returned 54.8C
After 8 mins, it returned 54.2C
After 10 mins, it returned 53.7C

It looks like CPU temperature isn't an issue here. 

While playing the 24/192 FLAC files, I ran vcgencmd measure_volts twice, separated by several minutes. Both times it returned volt=1.3563V
That's OK, isn't it?
--

[rongon]

I tried the various suggestions but I still get ticks/clicks during playback of 24-bit/192kHz FLAC files.
Since this only happens with my older RPi3B+, I'm going to have to assume the RPi is causing the problem.
I might just have to retire this one and get a new RPi4.
Or I might have to down-sample my 24/192 FLACs to 24/48, which seem to play fine.

Thanks everyone.

[Nutul]

I tried the various suggestions but I still get ticks/clicks during playback of 24-bit/192kHz FLAC files.
Since this only happens with my older RPi3B+, I'm going to have to assume the RPi is causing the problem.
I might just have to retire this one and get a new RPi4.
Or I might have to down-sample my 24/192 FLACs to 24/48, which seem to play fine.

Thanks everyone.

TLDR: buy a Pi4.

Then...the quickest answer I can think of, based on your description, is based on the following deductions:
1. the Pi3 seems "slow", or "overloaded" at doing so
2. feeding it with less-demanding processing power files (such as 48 kHz instead of 192 kHz) seems to "solve" the issue
3. this seems to only happen with the Pi3

In my opinion, you have better switch to at least a Pi4. Although I never experienced your clicks/pops/glitches with a Pi3, with my entire library, which consists of many > 16bit, and > 48 kHz files (single-disc FLACs + CUE, this I have to say, as IMHO it still can make a difference, at least when a track-change takes place...).

Nevertheless, I now employ a Pi4, since before the pandemic, and never had an issue. Same library (well... a little bit bigger, TBH, say by a 15%), but I do not consider the library size being an issue on a playback POV; only, eventually, during its rebuild / update / rescan...

Another thing that may be involved, is the "read speed" of the drive(s) your library resides on... and if a NAS is involved, rather than local USB drivers, the network speed / link-quality may (well... does) make a difference.

[Caesar]

I tried the various suggestions but I still get ticks/clicks during playback of 24-bit/192kHz FLAC files.
Since this only happens with my older RPi3B+, I'm going to have to assume the RPi is causing the problem.
I might just have to retire this one and get a new RPi4.
Or I might have to down-sample my 24/192 FLACs to 24/48, which seem to play fine.

Thanks everyone.

IMHO it is a matter of processing power.
I had the same issue with Pi3B+, upgrading to Pi5 solved it.