我正在尝试将我的 Sound Devices MixPre-D 作为 USB 音频接口连接到运行 Lubuntu 20.04 的笔记本电脑。MixPre-D 声称符合 USB 标准，旨在用作双工（输入和输出）音频接口。当我查看脉冲音量控制时，我在“输出设备”选项卡下看到了 MixPre-D，但在“输入设备”下没有看到。如果我转到脉冲音量控制中的“配置”选项卡，MixPre-D 的配置文件列为“模拟立体声输出”，并且没有“模拟立体声双工”的配置文件，根据我的另一张声卡，我认为它应该是这样的。
我已在 Windows 7 上试用过 Mixpre-D，它运行正常。我还在另一台机器上的另一个 Lubuntu 安装上试用过，它再次显示为输出设备。我已在不同的 USB 端口和不同的 USB 电缆上试用过，结果都一样。最后，我有另一个符合 USB 标准的接口，即 Zoom H2 录音机，它在 Lubuntu 和 Windows 机器上均运行正常。因此，似乎 ALSA 中存在某些问题，无法正确识别此特定设备。
MixPre-D 显示在 lsusb 和 aplay -l 中，但不显示在 arecord -l 中。当我查看 arecord -L 的详细信息时，它将 MixPre-D 显示为“USB 输出”。我似乎需要告诉 ALSA 该设备也是“USB 输入”，但我不知道该怎么做。任何帮助都将不胜感激！
以下是一些典型诊断的结果。
brian@Prolefeed-3:~$ lsusb
Bus 002 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 004: ID 04f2:b2da Chicony Electronics Co., Ltd thinkpad t430s camera
Bus 001 Device 003: ID 0a5c:21e6 Broadcom Corp. BCM20702 Bluetooth 4.0 [ThinkPad]
Bus 001 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 002: ID 0926:0208 Sound Devices MixPre-D
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
brian@Prolefeed-3:
brian@Prolefeed-3:~$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: ALC3202 Analog [ALC3202 Analog]
Subdevices: 0/1
Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 3: HDMI 0 [HDMI 0]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 7: HDMI 1 [HDMI 1]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 8: HDMI 2 [HDMI 2]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: MixPreD [MixPre-D], device 0: USB Audio [USB Audio]
Subdevices: 0/1
Subdevice #0: subdevice #0
brian@Prolefeed-3:
brian@Prolefeed-3:~$ arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: ALC3202 Analog [ALC3202 Analog]
Subdevices: 0/1
Subdevice #0: subdevice #0
brian@Prolefeed-3:
brian@Prolefeed-3:~$ arecord -L
default
Playback/recording through the PulseAudio sound server
surround21
2.1 Surround output to Front and Subwoofer speakers
surround40
4.0 Surround output to Front and Rear speakers
surround41
4.1 Surround output to Front, Rear and Subwoofer speakers
surround50
5.0 Surround output to Front, Center and Rear speakers
surround51
5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71
7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
null
Discard all samples (playback) or generate zero samples (capture)
samplerate
Rate Converter Plugin Using Samplerate Library
speexrate
Rate Converter Plugin Using Speex Resampler
jack
JACK Audio Connection Kit
oss
Open Sound System
pulse
PulseAudio Sound Server
upmix
Plugin for channel upmix (4,6,8)
vdownmix
Plugin for channel downmix (stereo) with a simple spacialization
sysdefault:CARD=PCH
HDA Intel PCH, ALC3202 Analog
Default Audio Device
front:CARD=PCH,DEV=0
HDA Intel PCH, ALC3202 Analog
Front speakers
dmix:CARD=PCH,DEV=0
HDA Intel PCH, ALC3202 Analog
Direct sample mixing device
dsnoop:CARD=PCH,DEV=0
HDA Intel PCH, ALC3202 Analog
Direct sample snooping device
hw:CARD=PCH,DEV=0
HDA Intel PCH, ALC3202 Analog
Direct hardware device without any conversions
plughw:CARD=PCH,DEV=0
HDA Intel PCH, ALC3202 Analog
Hardware device with all software conversions
usbstream:CARD=PCH
HDA Intel PCH
USB Stream Output
usbstream:CARD=MixPreD
MixPre-D
USB Stream Output
brian@Prolefeed-3:~$
brian@Prolefeed-3:~$ cat /proc/asound/cards
0 [PCH ]: HDA-Intel - HDA Intel PCH
HDA Intel PCH at 0xf2530000 irq 33
1 [MixPreD ]: USB-Audio - MixPre-D
Sound Devices MixPre-D at usb-0000:00:14.0-3, full speed
brian@Prolefeed-3:~$
brian@Prolefeed-3:~$ cat /proc/asound/devices
1: : sequencer
2: [ 0- 0]: digital audio playback
3: [ 0- 0]: digital audio capture
4: [ 0- 3]: digital audio playback
5: [ 0- 7]: digital audio playback
6: [ 0- 8]: digital audio playback
7: [ 0- 0]: hardware dependent
8: [ 0- 3]: hardware dependent
9: [ 0] : control
10: [ 1- 0]: digital audio playback
11: [ 1] : control
33: : timer
brian@Prolefeed-3:~$
答案1
解决了！显然，这是 Sound Devices 实施 USB 音频标准时的一个已知错误。请参阅此处的讨论：https://www.spinics.net/lists/stable/msg411289.html。
此补丁包含在Linux 内核 5.9.0（尽管在更新日志中没有记录）。因此，将 Lubuntu 升级到 5.9.0 内核（遵循此处的说明) 解决了这个问题。我的 MixPre-D 现在在 ALSA 和 Pulse 中显示为输出和输入设备。
brian@Prolefeed-3:~$ arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: ALC3202 Analog [ALC3202 Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: MixPreD [MixPre-D], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
brian@Prolefeed-3:~$
遗憾的是，Sound Devices 尚未修复其 USB 标准的实现，但至少我让它正常工作了。希望这能帮助其他处于类似情况的人。