raspberrypi
Audio stuttering and crackling when transferring data through pipe on Raspberry Pi OS Bookworm
Describe the bug
Audio playback is intermittently interrupted by stuttering and crackling noises when a data stream is transferred through a pipe using standard Linux utilities. The issue is especially noticeable when performing data-heavy operations such as piping /dev/zero through pv to /dev/null, and appears to be related to resource contention or scheduling.
Additional Information:
- The issue was first noticed during debugging of a custom application that processes data from a pipe.
- It was later confirmed to occur using only standard tools (cat, pv, mpg123).
- The CPU load remains relatively low when the issue occurs (25-40%).
- Appears to be either a scheduler latency issue, audio buffer underrun, or an I/O-related bottleneck affecting audio playback.
Steps to reproduce the behaviour
- Open a terminal and start audio playback (e.g., internet radio):
mpg123 -f 6554 https://strm112.1.fm/onelive_mobile_mp3
- In another terminal, run:
cat /dev/zero | pv -r > /dev/null
- Optionally, open Chromium and navigate to a simple web page, for example https://www.google.com to increase likelihood of issue manifesting. You can also try moving the mouse cursor over the browser page, which appears to increase the likelihood of the audio glitch occurring.
Expected Behavior: Audio should continue playing smoothly without interruptions, regardless of background data transfers or other light system activity.
Actual Behavior:
- Audio crackles intermittently or stutters heavily.
- In some cases, the audio becomes distorted and jittery immediately; in others, only mild crackling is noticed after several seconds.
- Severity varies based on system state and seems to be influenced by non-deterministic factors.
Note: The issue does not always manifest immediately and may require restarting the cat /dev/zero | pv -r > /dev/null command multiple times under different conditions. I have not identified a clear pattern or trigger, but once the audio disruption begins, it tends to persist consistently until the command cat /dev/zero | pv -r > /dev/null is restarted. Interestingly, restarting the same command - under seemingly identical system conditions (no change in background processes or overall system load), can result in normal, uninterrupted audio playback.
I also observed that when the audio stuttering and crackling occurs, the cat /dev/zero | pv -r > /dev/null command reports significantly reduced throughput. Under normal conditions, it shows a data rate of around 1.1 - 1.2 GiB/s, but during audio issues, the reported speed drops to 600-700 MiB/s with noticeable and very unstable fluctuations.
What’s particularly puzzling is that the issue may or may not occur under seemingly identical conditions. It appears to depend on some non-deterministic factors at the moment the command is executed.
Device (s)
Raspberry Pi 4 Mod. B
System
Raspberry Pi reference 2023-09-22 Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, 40f37458ae7cadea1aec913ae10b5e7008ebce0a, stage4
vcgencmd version Apr 30 2025 13:33:39 Copyright (c) 2012 Broadcom version 5560078dcc8591a00f57b9068d13e5544aeef3aa (clean) (release) (start)
uname -a Linux zx80 6.12.25+rpt-rpi-v8 #1 SMP PREEMPT Debian 1:6.12.25-1+rpt1 (2025-04-30) aarch64 GNU/Linux
Logs
No relevant error messages appear in the dmesg log when the issue occurs.
Additional context
Similar audio interruptions and crackling can also be observed when opening moderately large schematic files in KiCad.
Are you using HDMI audio or the headphone jack? The two involve processing at different levels (ALSA for HDMI and the firmware for the headphone jack).
Synchronous or asynchronous?
Transfer Type Isochronous
Synch Type Synchronous
With what kind of quality settings?
Packet Size = 72
Momentary freq = 48000 Hz (0x6.0000)
Format: S32_LE
Channels: 2
Endpoint: 0x01 (1 OUT) (SYNC)
Rates: 44100, 48000, 96000, 192000, 384000
Data packet interval: 125 us
Bits: 32
Channel map: FL FR
I don't know what kind of latency tolerance that give you, but obviously not enough. Also, 32-bit samples are a bit excessive, but less so than 24-bit stereo at 384kHz.
If you aren't actively using the initramfs (e.g. to load an exotic network interface driver before using an NFS rootfs), you might want to try one of the new -rt (realtime) kernel builds (althought apart from booting it and seeing that normal things seem to work, I have no real experience of it).
To install the RT kernel:
$ sudo WANT_32BIT=0 WANT_64BIT=0 WANT_PI4=0 WANT_PI5=0 WANT_64BIT_RT=1 rpi-update rpi-6.12.y
Note that you will need to specify the branch name (rpi-6.12.y) - the normal rpi-update releases don't currently include the -rt builds. Also, back up any important data first - this is beta software.
You can switch to the new kernel using "kernel=kernel8_rt.img". And, if something goes horribly wrong, you should be able to revert to the previous kernel by commenting out or deleting that line.
I'm testing with:
- Pi 4B
- Asynchronous USB3 DAC + headphone amp
- Ethernet
It's working fine for me. With your mpg123 stream I get ~1000MB/s through the pipe. Switching to a YouTube music stream (1080p HD video stream, but an animated static image rather than a full music video), and that drops down to 500MB/s.
Not a single stutter. Running both streams together and mixing the audio it drops to 400MB/s, still with flawless audio (although I wouldn't recommend the Sleep Token vs. Celine Dion combo).
And that's with the default 64-bit kernel. Same with WiFi instead of Ethernet.
Final comment - Sleep Token's Emergence vs Spandau Ballet's True works surprisingly well.
@pelwell does the DAC also work fine under those conditions if plugged into one of the USB2.0 ports?
@zxmak please post a full sudo lsusb -v for your DAC.
Yes. Mine says:
Bus 001 Device 008: ID 20b1:3008 XMOS Ltd iFi (by AMR) HD USB Audio
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 2.00
bDeviceClass 239 Miscellaneous Device
bDeviceSubClass 2
bDeviceProtocol 1 Interface Association
bMaxPacketSize0 64
idVendor 0x20b1 XMOS Ltd
idProduct 0x3008
bcdDevice 1.50
iManufacturer 1 iFi (by AMR)
iProduct 3 iFi (by AMR) HD USB Audio
iSerial 2 000
bNumConfigurations 2
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 0x0135
bNumInterfaces 4
bConfigurationValue 1
iConfiguration 0
bmAttributes 0xc0
Self Powered
MaxPower 0mA
Interface Association:
bLength 8
bDescriptorType 11
bFirstInterface 0
bInterfaceCount 2
bFunctionClass 1 Audio
bFunctionSubClass 0
bFunctionProtocol 32
iFunction 0
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 1 Audio
bInterfaceSubClass 1 Control Device
bInterfaceProtocol 32
iInterface 3 iFi (by AMR) HD USB Audio
AudioControl Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 1 (HEADER)
bcdADC 2.00
bCategory 8
wTotalLength 0x0048
bmControls 0x00
AudioControl Interface Descriptor:
bLength 8
bDescriptorType 36
bDescriptorSubtype 10 (CLOCK_SOURCE)
bClockID 41
bmAttributes 3 Internal programmable clock
bmControls 0x07
Clock Frequency Control (read/write)
Clock Validity Control (read-only)
bAssocTerminal 0
iClockSource 9 iFi (by AMR) Internal Clock
AudioControl Interface Descriptor:
bLength 8
bDescriptorType 36
bDescriptorSubtype 11 (CLOCK_SELECTOR)
bClockID 40
bNrInPins 1
baCSourceID(0) 41
bmControls 0x03
Clock Selector Control (read/write)
iClockSelector 8 iFi (by AMR) Clock Selector
AudioControl Interface Descriptor:
bLength 17
bDescriptorType 36
bDescriptorSubtype 2 (INPUT_TERMINAL)
bTerminalID 2
wTerminalType 0x0101 USB Streaming
bAssocTerminal 0
bCSourceID 40
bNrChannels 2
bmChannelConfig 0x00000000
iChannelNames 11 Analogue 1
bmControls 0x0000
iTerminal 6 iFi (by AMR) HD USB Audio
AudioControl Interface Descriptor:
bLength 18
bDescriptorType 36
bDescriptorSubtype 6 (FEATURE_UNIT)
bUnitID 10
bSourceID 2
bmaControls(0) 0x0000000f
Mute Control (read/write)
Volume Control (read/write)
bmaControls(1) 0x0000000f
Mute Control (read/write)
Volume Control (read/write)
bmaControls(2) 0x0000000f
Mute Control (read/write)
Volume Control (read/write)
iFeature 0
AudioControl Interface Descriptor:
bLength 12
bDescriptorType 36
bDescriptorSubtype 3 (OUTPUT_TERMINAL)
bTerminalID 20
wTerminalType 0x0301 Speaker
bAssocTerminal 0
bSourceID 10
bCSourceID 40
bmControls 0x0000
iTerminal 0
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 4 iFi (by AMR) HD USB Audio
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 1
bNumEndpoints 2
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 4 iFi (by AMR) HD USB Audio
AudioStreaming Interface Descriptor:
bLength 16
bDescriptorType 36
bDescriptorSubtype 1 (AS_GENERAL)
bTerminalLink 2
bmControls 0x00
bFormatType 1
bmFormats 0x00000001
PCM
bNrChannels 2
bmChannelConfig 0x00000000
iChannelNames 11 Analogue 1
AudioStreaming Interface Descriptor:
bLength 6
bDescriptorType 36
bDescriptorSubtype 2 (FORMAT_TYPE)
bFormatType 1 (FORMAT_TYPE_I)
bSubslotSize 4
bBitResolution 32
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x01 EP 1 OUT
bmAttributes 5
Transfer Type Isochronous
Synch Type Asynchronous
Usage Type Data
wMaxPacketSize 0x0308 1x 776 bytes
bInterval 1
AudioStreaming Endpoint Descriptor:
bLength 8
bDescriptorType 37
bDescriptorSubtype 1 (EP_GENERAL)
bmAttributes 0x00
bmControls 0x00
bLockDelayUnits 2 Decoded PCM samples
wLockDelay 0x0008
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 17
Transfer Type Isochronous
Synch Type None
Usage Type Feedback
wMaxPacketSize 0x0004 1x 4 bytes
bInterval 4
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 2
bNumEndpoints 2
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 4 iFi (by AMR) HD USB Audio
AudioStreaming Interface Descriptor:
bLength 16
bDescriptorType 36
bDescriptorSubtype 1 (AS_GENERAL)
bTerminalLink 2
bmControls 0x00
bFormatType 1
bmFormats 0x00000001
PCM
bNrChannels 2
bmChannelConfig 0x00000000
iChannelNames 11 Analogue 1
AudioStreaming Interface Descriptor:
bLength 6
bDescriptorType 36
bDescriptorSubtype 2 (FORMAT_TYPE)
bFormatType 1 (FORMAT_TYPE_I)
bSubslotSize 2
bBitResolution 16
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x01 EP 1 OUT
bmAttributes 5
Transfer Type Isochronous
Synch Type Asynchronous
Usage Type Data
wMaxPacketSize 0x0184 1x 388 bytes
bInterval 1
AudioStreaming Endpoint Descriptor:
bLength 8
bDescriptorType 37
bDescriptorSubtype 1 (EP_GENERAL)
bmAttributes 0x00
bmControls 0x00
bLockDelayUnits 2 Decoded PCM samples
wLockDelay 0x0008
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 17
Transfer Type Isochronous
Synch Type None
Usage Type Feedback
wMaxPacketSize 0x0004 1x 4 bytes
bInterval 4
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 3
bNumEndpoints 2
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 4 iFi (by AMR) HD USB Audio
AudioStreaming Interface Descriptor:
bLength 16
bDescriptorType 36
bDescriptorSubtype 1 (AS_GENERAL)
bTerminalLink 2
bmControls 0x00
bFormatType 1
bmFormats 0x80000000
bNrChannels 2
bmChannelConfig 0x00000000
iChannelNames 11 Analogue 1
AudioStreaming Interface Descriptor:
bLength 6
bDescriptorType 36
bDescriptorSubtype 2 (FORMAT_TYPE)
bFormatType 1 (FORMAT_TYPE_I)
bSubslotSize 4
bBitResolution 32
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x01 EP 1 OUT
bmAttributes 5
Transfer Type Isochronous
Synch Type Asynchronous
Usage Type Data
wMaxPacketSize 0x0308 1x 776 bytes
bInterval 1
AudioStreaming Endpoint Descriptor:
bLength 8
bDescriptorType 37
bDescriptorSubtype 1 (EP_GENERAL)
bmAttributes 0x00
bmControls 0x00
bLockDelayUnits 2 Decoded PCM samples
wLockDelay 0x0008
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 17
Transfer Type Isochronous
Synch Type None
Usage Type Feedback
wMaxPacketSize 0x0004 1x 4 bytes
bInterval 4
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 2
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 254 Application Specific Interface
bInterfaceSubClass 1 Device Firmware Update
bInterfaceProtocol 1
iInterface 10 iFi (by AMR) DFU
Device Firmware Upgrade Interface Descriptor:
bLength 9
bDescriptorType 33
bmAttributes 7
Will Not Detach
Manifestation Tolerant
Upload Supported
Download Supported
wDetachTimeout 250 milliseconds
wTransferSize 64 bytes
bcdDFUVersion 1.10
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 3
bAlternateSetting 0
bNumEndpoints 1
bInterfaceClass 3 Human Interface Device
bInterfaceSubClass 0
bInterfaceProtocol 0
iInterface 14 iFi (by AMR) HD USB Audio (MQA HID)
HID Device Descriptor:
bLength 9
bDescriptorType 33
bcdHID 1.10
bCountryCode 0 Not supported
bNumDescriptors 1
bDescriptorType 34 Report
wDescriptorLength 21
Report Descriptors:
** UNAVAILABLE **
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x83 EP 3 IN
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 8
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 0x0135
bNumInterfaces 4
bConfigurationValue 1
iConfiguration 0
bmAttributes 0xc0
Self Powered
MaxPower 0mA
Interface Association:
bLength 8
bDescriptorType 11
bFirstInterface 0
bInterfaceCount 2
bFunctionClass 1 Audio
bFunctionSubClass 0
bFunctionProtocol 32
iFunction 0
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 1 Audio
bInterfaceSubClass 1 Control Device
bInterfaceProtocol 32
iInterface 3 iFi (by AMR) HD USB Audio
AudioControl Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 1 (HEADER)
bcdADC 2.00
bCategory 8
wTotalLength 0x0048
bmControls 0x00
AudioControl Interface Descriptor:
bLength 8
bDescriptorType 36
bDescriptorSubtype 10 (CLOCK_SOURCE)
bClockID 41
bmAttributes 3 Internal programmable clock
bmControls 0x07
Clock Frequency Control (read/write)
Clock Validity Control (read-only)
bAssocTerminal 0
iClockSource 9 iFi (by AMR) Internal Clock
AudioControl Interface Descriptor:
bLength 8
bDescriptorType 36
bDescriptorSubtype 11 (CLOCK_SELECTOR)
bClockID 40
bNrInPins 1
baCSourceID(0) 41
bmControls 0x03
Clock Selector Control (read/write)
iClockSelector 8 iFi (by AMR) Clock Selector
AudioControl Interface Descriptor:
bLength 17
bDescriptorType 36
bDescriptorSubtype 2 (INPUT_TERMINAL)
bTerminalID 2
wTerminalType 0x0101 USB Streaming
bAssocTerminal 0
bCSourceID 40
bNrChannels 2
bmChannelConfig 0x00000000
iChannelNames 11 Analogue 1
bmControls 0x0000
iTerminal 6 iFi (by AMR) HD USB Audio
AudioControl Interface Descriptor:
bLength 18
bDescriptorType 36
bDescriptorSubtype 6 (FEATURE_UNIT)
bUnitID 10
bSourceID 2
bmaControls(0) 0x0000000f
Mute Control (read/write)
Volume Control (read/write)
bmaControls(1) 0x0000000f
Mute Control (read/write)
Volume Control (read/write)
bmaControls(2) 0x0000000f
Mute Control (read/write)
Volume Control (read/write)
iFeature 0
AudioControl Interface Descriptor:
bLength 12
bDescriptorType 36
bDescriptorSubtype 3 (OUTPUT_TERMINAL)
bTerminalID 20
wTerminalType 0x0301 Speaker
bAssocTerminal 0
bSourceID 10
bCSourceID 40
bmControls 0x0000
iTerminal 0
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 4 iFi (by AMR) HD USB Audio
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 1
bNumEndpoints 2
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 4 iFi (by AMR) HD USB Audio
AudioStreaming Interface Descriptor:
bLength 16
bDescriptorType 36
bDescriptorSubtype 1 (AS_GENERAL)
bTerminalLink 2
bmControls 0x00
bFormatType 1
bmFormats 0x00000001
PCM
bNrChannels 2
bmChannelConfig 0x00000000
iChannelNames 11 Analogue 1
AudioStreaming Interface Descriptor:
bLength 6
bDescriptorType 36
bDescriptorSubtype 2 (FORMAT_TYPE)
bFormatType 1 (FORMAT_TYPE_I)
bSubslotSize 4
bBitResolution 32
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x01 EP 1 OUT
bmAttributes 5
Transfer Type Isochronous
Synch Type Asynchronous
Usage Type Data
wMaxPacketSize 0x0308 1x 776 bytes
bInterval 1
AudioStreaming Endpoint Descriptor:
bLength 8
bDescriptorType 37
bDescriptorSubtype 1 (EP_GENERAL)
bmAttributes 0x00
bmControls 0x00
bLockDelayUnits 2 Decoded PCM samples
wLockDelay 0x0008
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 17
Transfer Type Isochronous
Synch Type None
Usage Type Feedback
wMaxPacketSize 0x0004 1x 4 bytes
bInterval 4
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 2
bNumEndpoints 2
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 4 iFi (by AMR) HD USB Audio
AudioStreaming Interface Descriptor:
bLength 16
bDescriptorType 36
bDescriptorSubtype 1 (AS_GENERAL)
bTerminalLink 2
bmControls 0x00
bFormatType 1
bmFormats 0x00000001
PCM
bNrChannels 2
bmChannelConfig 0x00000000
iChannelNames 11 Analogue 1
AudioStreaming Interface Descriptor:
bLength 6
bDescriptorType 36
bDescriptorSubtype 2 (FORMAT_TYPE)
bFormatType 1 (FORMAT_TYPE_I)
bSubslotSize 2
bBitResolution 16
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x01 EP 1 OUT
bmAttributes 5
Transfer Type Isochronous
Synch Type Asynchronous
Usage Type Data
wMaxPacketSize 0x0184 1x 388 bytes
bInterval 1
AudioStreaming Endpoint Descriptor:
bLength 8
bDescriptorType 37
bDescriptorSubtype 1 (EP_GENERAL)
bmAttributes 0x00
bmControls 0x00
bLockDelayUnits 2 Decoded PCM samples
wLockDelay 0x0008
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 17
Transfer Type Isochronous
Synch Type None
Usage Type Feedback
wMaxPacketSize 0x0004 1x 4 bytes
bInterval 4
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 3
bNumEndpoints 2
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 4 iFi (by AMR) HD USB Audio
AudioStreaming Interface Descriptor:
bLength 16
bDescriptorType 36
bDescriptorSubtype 1 (AS_GENERAL)
bTerminalLink 2
bmControls 0x00
bFormatType 1
bmFormats 0x80000000
bNrChannels 2
bmChannelConfig 0x00000000
iChannelNames 11 Analogue 1
AudioStreaming Interface Descriptor:
bLength 6
bDescriptorType 36
bDescriptorSubtype 2 (FORMAT_TYPE)
bFormatType 1 (FORMAT_TYPE_I)
bSubslotSize 4
bBitResolution 32
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x01 EP 1 OUT
bmAttributes 5
Transfer Type Isochronous
Synch Type Asynchronous
Usage Type Data
wMaxPacketSize 0x0308 1x 776 bytes
bInterval 1
AudioStreaming Endpoint Descriptor:
bLength 8
bDescriptorType 37
bDescriptorSubtype 1 (EP_GENERAL)
bmAttributes 0x00
bmControls 0x00
bLockDelayUnits 2 Decoded PCM samples
wLockDelay 0x0008
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 17
Transfer Type Isochronous
Synch Type None
Usage Type Feedback
wMaxPacketSize 0x0004 1x 4 bytes
bInterval 4
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 2
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 254 Application Specific Interface
bInterfaceSubClass 1 Device Firmware Update
bInterfaceProtocol 1
iInterface 10 iFi (by AMR) DFU
Device Firmware Upgrade Interface Descriptor:
bLength 9
bDescriptorType 33
bmAttributes 7
Will Not Detach
Manifestation Tolerant
Upload Supported
Download Supported
wDetachTimeout 250 milliseconds
wTransferSize 64 bytes
bcdDFUVersion 1.10
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 3
bAlternateSetting 0
bNumEndpoints 1
bInterfaceClass 3 Human Interface Device
bInterfaceSubClass 0
bInterfaceProtocol 0
iInterface 14 iFi (by AMR) HD USB Audio (MQA HID)
HID Device Descriptor:
bLength 9
bDescriptorType 33
bcdHID 1.10
bCountryCode 0 Not supported
bNumDescriptors 1
bDescriptorType 34 Report
wDescriptorLength 21
Report Descriptors:
** UNAVAILABLE **
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x83 EP 3 IN
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 8
Device Qualifier (for other device speed):
bLength 10
bDescriptorType 6
bcdUSB 2.00
bDeviceClass 239 Miscellaneous Device
bDeviceSubClass 2
bDeviceProtocol 1 Interface Association
bMaxPacketSize0 64
bNumConfigurations 2
Device Status: 0x0001
Self Powered
Yes, the USB DAC is connected to a USB 2.0 port via a USB 2.0 hub, along with a keyboard and mouse. Additionally, I am using 1.5 GB of zram swap (sudo apt install zram-tools, SIZE=1536), in case that is relevant.
WiFi and Bluetooth interfaces are disabled. Ethernet adapter is RPI4 onboard, configured with NetworkManager to use static IP.
The sound stuttering is not consistently reproducible. Sometimes audio playback remains smooth, while other times it begins to stutter. The only apparent variable is the timing of when the pipe streaming process is started.
For example when I run the pipe streaming process and it trigger strong audio stuttering, and then simply stopping it with Ctrl+C and restarting the same command, it may result in normal audio playback without any issues.
I have also occasionally noticed brief audio dropouts when loading web pages in the Firefox browser, but it happens rarely.
I suspect the issue might be related to CPU core assignment - specifically, which core is handling audio playback and which core the pipe streaming process is scheduled on at the time of execution.