Constant audio underflow on Raspi Zero 2W

Helly everbody,

first, I really appreciate your work here. I completely dropped my old Multi-Room system and build a new one around Music Assistant and Sendspin. Love it!

But I have problems with one of my sendspin clients.

This is running on a Raspi Zero 2W, With Raspi OS Lite on Debian 13.4 and Sendspin 5.9.0.
I constantly get Audio underflows. Every 1-2 minutes, sometimes more.

WARNING:sendspin.audio:Audio underflow detected; requesting re-anchor

First I thougt this is a weak wifi connection. I disabled wifi-sleep, disable cpu throttling
echo "performance" | sudo tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
disabled bluetooth, made a firmware upgrade. But nothing improved the situation.

I also moved the PI directly next to the Wifi-AP. The number of underflows dropped down to every 5min, but they are still there.

So from my point of view, this is the best wifi situation I can give to the PI. Therefore the underflows must also be caused by another issue.
But I dont know how to proceed. Any ideas from your site?

Or is the wifi from the PI that bad, that even the best connection is not fast enough?
All other clients in the wifi are working fine. The wifi itself is very stable. Even my HA Voice PE, which is placed farther away from the Wifi-AP is working fine with sendspin.

In the past it feels like, the situation was better. I was around sendspin 1.x and then updated to 5.x. Not fully sure, but I think the problems started getting worse with the update. Before I had a dropout every 30-60min.

Can you run top to see your CPU usage. Also make sure hardware volume is enabled. If that still happens, try setting it to 16 or 32 bit quality.

If certain Python dependencies fail to compile or are missing, we fall back to software-based calculations in Python, which are slow.

top gives me around 3-6% CPU and 24% mem in idle for sendspin. If I stream music, CPU is up to 12%, Mem goes to 25-28%.
I enabled hardware_volume via settings-daemon.json, no difference.

I tried also different audio format settings in MA. But only 16/24bit. There is no 32bit quality. Also no difference.

How can I check the Python dependencies?

Avahi-daemon is eating a lot of cpu...

I disabled avahi-daemon, no improvement on my problem.
I tried a external USB-wifi antenna, which gives me 5GHz wifi, better signal etc. But also no improvement.

I found this in the logs:
sendspin[1435]: WARNING:sendspin.cli:No volume control available for device 'default' (no ALSA mixer controls and PulseAudio/PipeWire not reachable), falling back to software volume control

#238 should have fixed this. Can you update and try again?

Unfortunately the problem persists. I am on sendspin-cli 7.1.0
Raspi Zero with Wifi and Hardwired Raspi 3 shows the same problem.

10:51:48 Stream STARTED: 3 chunks, 0.29 second buffered
10:51:51 Audio underflow deected; requesting re-anchor
10:51:52 Cleared audio queue after underflow (deferred from audio thread)

Logs are written off. Cannot copy at the moment. But should be enough?

Software volume control is the thing here that messes with things. It's very CPU intensive.

How can I get rid of this? I use this Pimoroni Audio DAC Shim which sends a fixed line-level output. I control the volume on my amplified speakers. So I dont need volume control at all.

If I use this

{
  "use_hardware_volume": true,
  "player_volume": 100
}

I still get the log that there is no volume control available and he is falling back to software volume.

I created a file

# /bin/sh
exit 0

and used this as a hook for volume.
Sendspin seems to use now hardware volume. But still no improvement.

The wired raspi has also the problem.

I some kind I have an improvement. It seems that it happens less often, but it still happens :(

I tried also another way:


"audio_device": "hw:0,0",
"audio_format": "pcm:48000:16:2",
"use_hardware_volume": true,

gave me this

Apr 29 22:26:43 esszimmer-music systemd[1]: Started sendspin.service - Sendspin Multi-Room Audio Client.
Apr 29 22:26:47 esszimmer-music sendspin[8211]: INFO:sendspin.audio_devices:Using audio device hw:0,0: hw:0,0
Apr 29 22:26:47 esszimmer-music sendspin[8211]: DEBUG:sendspin.alsa_volume:ALSA card 0: selected preferred mixer element 'Master'
Apr 29 22:26:47 esszimmer-music sendspin[8211]: INFO:sendspin.cli:Using ALSA mixer volume control: card 0, element 'Master'
Apr 29 22:26:49 esszimmer-music sendspin[8211]: INFO:sendspin.cli:Using preferred audio format: pcm:48000:16:2
Apr 29 22:26:49 esszimmer-music sendspin[8211]: INFO:sendspin.daemon.daemon:Starting Sendspin daemon: sendspin-cli-esszimmer-music
Apr 29 22:26:49 esszimmer-music sendspin[8211]: INFO:sendspin.daemon.daemon:Listening for server connections on port 8928 (mDNS: _sendspin._tcp.local.)
Apr 29 22:26:49 esszimmer-music sendspin[8211]: INFO:aiosendspin.client.listener:ClientListener started on port 8928, path /sendspin
Apr 29 22:26:50 esszimmer-music sendspin[8211]: DEBUG:aiosendspin.client.listener:Incoming server connection from 10.0.20.7
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:sendspin.daemon.daemon:Server connected
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:sendspin.audio_devices:Detected 32 supported audio formats (FLAC + PCM)
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:aiosendspin.client.client:Connected to server 'Music Assistant' (49a640b7995a4eb89d37ca73baf4d38a) version 1
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:aiosendspin.client.client:Handshake with server complete
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:mpris_api:PatchedMprisService started.
Apr 29 22:26:50 esszimmer-music sendspin[8211]: DEBUG:aiosendspin_mpris.mpris:Attached MPRIS listeners to SendspinClient
Apr 29 22:26:50 esszimmer-music sendspin[8211]: DEBUG:asyncio:Using selector: EpollSelector
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:aiosendspin_mpris.mpris:MPRIS interface started
Apr 29 22:26:50 esszimmer-music sendspin[8211]: WARNING:aiosendspin_mpris.mpris_service:MPRIS not available: DBus address error
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:aiosendspin.client.client:Stream started with codec pcm
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:mpris_api:PatchedMprisService stopped.
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:aiosendspin.client.listener:mDNS advertising client 'sendspin-cli-esszimmer-music' on port 8928 with path /sendspin
Apr 29 22:26:50 esszimmer-music sendspin[8211]: DEBUG:aiosendspin.client.listener:Incoming server connection from 10.0.20.7
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:sendspin.daemon.daemon:Server connected
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:sendspin.audio_devices:Detected 32 supported audio formats (FLAC + PCM)
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:aiosendspin.client.client:Connected to server 'Music Assistant' (49a640b7995a4eb89d37ca73baf4d38a) version 1
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:aiosendspin.client.client:Handshake with server complete
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:sendspin.daemon.daemon:Switching to server 'Music Assistant' (discovery)
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:aiosendspin_mpris.mpris:MPRIS interface stopped
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:mpris_api:PatchedMprisService started.
Apr 29 22:26:50 esszimmer-music sendspin[8211]: DEBUG:aiosendspin_mpris.mpris:Attached MPRIS listeners to SendspinClient
Apr 29 22:26:50 esszimmer-music sendspin[8211]: DEBUG:asyncio:Using selector: EpollSelector
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:aiosendspin_mpris.mpris:MPRIS interface started
Apr 29 22:26:50 esszimmer-music sendspin[8211]: WARNING:aiosendspin_mpris.mpris_service:MPRIS not available: DBus address error
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:sendspin.daemon.daemon:Server disconnected
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:aiohttp.access:10.0.20.7 [29/Apr/2026:22:26:50 +0200] "GET /sendspin HTTP/1.1" 101 0 "-" "Music Assistant/2.8.5 aiohttp/3.13.5 Python/3.13"
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:mpris_api:PatchedMprisService stopped.
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:aiosendspin.client.client:Stream started with codec pcm
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:sendspin.daemon.daemon:Audio format: pcm 48000Hz/16-bit/2ch
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:sendspin.audio:Audio stream configured: codec=pcm, sample_rate=48000, channels=2, bit_depth=16, blocksize=2048, latency=high, output_latency=42.7 ms, device=hw:0,0
Apr 29 22:26:50 esszimmer-music sendspin[8211]: INFO:sendspin.audio:Stream STARTED: 8 chunks, 0.20 seconds buffered
Apr 29 22:26:50 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: 112.9 ms, buffer: 0.47 s, speed: 100.00%, played: 48000, inserted: 0, dropped: 0, callback: 535.0 µs
Apr 29 22:26:51 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -25.0 ms, buffer: 5.50 s, speed: 98.02%, played: 48952, inserted: 952, dropped: 0, callback: 1565.2 µs
Apr 29 22:26:52 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -36.6 ms, buffer: 9.30 s, speed: 98.70%, played: 48622, inserted: 622, dropped: 0, callback: 1117.4 µs
Apr 29 22:26:53 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -80.7 ms, buffer: 12.70 s, speed: 97.16%, played: 49361, inserted: 1361, dropped: 0, callback: 2139.4 µs
Apr 29 22:26:54 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -58.9 ms, buffer: 16.90 s, speed: 96.44%, played: 49710, inserted: 1710, dropped: 0, callback: 2473.5 µs
Apr 29 22:26:55 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -38.3 ms, buffer: 20.62 s, speed: 97.56%, played: 49169, inserted: 1169, dropped: 0, callback: 1809.8 µs
Apr 29 22:26:57 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -28.2 ms, buffer: 23.88 s, speed: 98.19%, played: 48871, inserted: 871, dropped: 0, callback: 1436.9 µs
Apr 29 22:26:58 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -4.3 ms, buffer: 29.57 s, speed: 99.17%, played: 48398, inserted: 398, dropped: 0, callback: 893.9 µs

Apr 29 22:27:48 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -0.2 ms, buffer: 30.00 s, speed: 100.00%, played: 48000, inserted: 0, dropped: 0, callback: 343.2 µs
Apr 29 22:27:49 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -0.8 ms, buffer: 29.95 s, speed: 100.00%, played: 48000, inserted: 0, dropped: 0, callback: 366.6 µs
Apr 29 22:27:50 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -1.3 ms, buffer: 29.85 s, speed: 100.00%, played: 48000, inserted: 0, dropped: 0, callback: 411.3 µs
Apr 29 22:27:51 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -1.9 ms, buffer: 29.98 s, speed: 100.00%, played: 48000, inserted: 0, dropped: 0, callback: 322.5 µs
Apr 29 22:27:52 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -2.3 ms, buffer: 30.02 s, speed: 99.93%, played: 48033, inserted: 33, dropped: 0, callback: 372.1 µs
Apr 29 22:27:53 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -2.5 ms, buffer: 30.02 s, speed: 99.88%, played: 48059, inserted: 59, dropped: 0, callback: 416.0 µs
Apr 29 22:27:54 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -2.5 ms, buffer: 30.05 s, speed: 99.88%, played: 48059, inserted: 59, dropped: 0, callback: 430.4 µs
Apr 29 22:27:55 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -2.4 ms, buffer: 30.00 s, speed: 99.87%, played: 48064, inserted: 64, dropped: 0, callback: 512.7 µs
Apr 29 22:27:56 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -2.3 ms, buffer: 29.82 s, speed: 99.88%, played: 48058, inserted: 58, dropped: 0, callback: 566.3 µs
Apr 29 22:27:57 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -1.9 ms, buffer: 30.02 s, speed: 99.93%, played: 48033, inserted: 33, dropped: 0, callback: 389.2 µs
Apr 29 22:27:58 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -1.6 ms, buffer: 30.00 s, speed: 100.00%, played: 48000, inserted: 0, dropped: 0, callback: 309.7 µs
Apr 29 22:27:59 esszimmer-music sendspin[8211]: WARNING:sendspin.audio:Audio underflow detected; requesting re-anchor
Apr 29 22:27:59 esszimmer-music sendspin[8211]: INFO:sendspin.audio:Cleared audio queue after underflow (deferred from audio thread)
Apr 29 22:27:59 esszimmer-music sendspin[8211]: INFO:sendspin.audio:Stream STARTED: 8 chunks, 0.20 seconds buffered
Apr 29 22:28:28 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -43.0 ms, buffer: 29.70 s, speed: 100.00%, played: 48000, inserted: 0, dropped: 0, callback: 175.7 µs
Apr 29 22:28:29 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -24.9 ms, buffer: 29.82 s, speed: 98.50%, played: 48719, inserted: 719, dropped: 0, callback: 1321.0 µs
Apr 29 22:28:30 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -15.0 ms, buffer: 29.80 s, speed: 98.96%, played: 48499, inserted: 499, dropped: 0, callback: 1007.2 µs
Apr 29 22:28:31 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -8.2 ms, buffer: 29.82 s, speed: 99.42%, played: 48276, inserted: 276, dropped: 0, callback: 1036.3 µs
Apr 29 22:28:32 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -3.9 ms, buffer: 29.85 s, speed: 99.67%, played: 48158, inserted: 158, dropped: 0, callback: 563.2 µs
Apr 29 22:28:33 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -1.5 ms, buffer: 29.82 s, speed: 99.88%, played: 48057, inserted: 57, dropped: 0, callback: 397.9 µs
Apr 29 22:28:34 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -0.4 ms, buffer: 29.75 s, speed: 100.00%, played: 48000, inserted: 0, dropped: 0, callback: 310.0 µs
Apr 29 22:28:36 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -0.8 ms, buffer: 29.82 s, speed: 100.00%, played: 48000, inserted: 0, dropped: 0, callback: 326.4 µs
Apr 29 22:28:37 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -1.1 ms, buffer: 29.88 s, speed: 100.00%, played: 48000, inserted: 0, dropped: 0, callback: 358.4 µs
Apr 29 22:28:38 esszimmer-music sendspin[8211]: DEBUG:sendspin.audio:Sync error: -1.2 ms, buffer: 29.75 s, speed: 100.00%, played: 48000, inserted: 0, dropped: 0, callback: 404.7 µs

I think I found the problem.
I tried sendspin with a esp32, thinking that this must work, surprisingly it does not.
Then I started investigating further my wifi. initially I thought the Wifi and therefore my whole network isnt the problem, because a hardwired Raspi showed the same problems.

But then I discovered that one of my Access Points hab nearly 100% use of airtime. First I thought my printer was flooding my network with mDNS announcements. But the real reason was my Homebridge. This flooded the network with mDNS announcements. The printer just tried to answer all these announcements and used all the airtime.
But the mDNS flood seems to be the reason that also the wired Raspi had problems.

I changed the mDNS advertiser in Homebridge to Avahi, prior it was Bonjour.

At the moment it is running for nearly 1h without a single audio underflow...

Excellent that it works. Thanks for sharing the problem, that will help us in the future.

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Constant audio underflow on Raspi Zero 2W #216

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Constant audio underflow on Raspi Zero 2W #216

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balloob commented on Apr 10, 2026

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