How to dig a Raspberry Pi USB audio troubles

I did some experiments about using audio output on Raspberry Pi. This is the note of what I did.

Photo by C D-X on Unsplash

First of all

I haven’t completed my work yet. So I can’t share any sample codes. This article is just a note about how to investigate the audio output on Raspberry Pi.

Background

I wanted to make my own assistant controlled by voice interface for a long. Then I happened to get a PlayStation Eye. So I thought it was a good time to do it.

PlayStation Eye - Wikipedia

However, it wasn’t more straightforward than I thought. It didn’t work just by plugging the USB cable into Raspberry Pi. The problem is that the following test command didn't work.

speaker-test -c2 -twav -l3 -D plughw:1,0

I needed to investigate the settings of its audio.

What I did

First of all, I thought the Raspberry Pi didn’t detect the PlayStation Eye as a device. So I checked the connected device data using the command.

$ cat /proc/asound/cards
 0 [Headphones     ]: bcm2835_headphonbcm2835 Headphones - bcm2835 Headphones
                      bcm2835 Headphones
 1 [vc4hdmi        ]: vc4-hdmi - vc4-hdmi
                      vc4-hdmi
 2 [CameraB404271  ]: USB-Audio - USB Camera-B4.04.27.1
                      OmniVision Technologies, Inc. USB Camera-B4.04.27.1 at usb-3f980000.usb-1.3, hi

The command cat /proc/asound/cards is also used to display a list of available audio devices (sound cards) on a Linux system. This command provides detailed information on the audio devices installed in or connected to the system.

Proc Files of ALSA Drivers - The Linux Kernel documentation

Alsa Opensrc Org - Independent ALSA and linux audio support site

Then the CameraB404271 was my PlayStation Eye. Also, I checked the audio devices using the following command as well.

$ aplay -L
default
    Playback/recording through the PulseAudio sound server
null
    Discard all samples (playback) or generate zero samples (capture)
jack
    JACK Audio Connection Kit
pulse
    PulseAudio Sound Server
...
usbstream:CARD=CameraB404271
    USB Camera-B4.04.27.1
    USB Stream Output

The aplay -L command is used to display information about ALSA (Advanced Linux Sound Architecture) sound cards and audio devices. aplay is part of the ALSA utility and provides a variety of sound playback-related information related to sound playback.

https://linux.die.net/man/1/aplay

Based on the information that I got at the moment, my PlayStation Eye was detected as an audio device by Raspberry Pi properly. Then I started to get suspicious of the driver. I checked the audio driver with the following command.

cat /proc/asound/modules
 0 snd_bcm2835
 1 (efault)
 2 snd_usb_audio

It said there was a driver for USB audio. So it might not go well with PlayStation Eye. So I bought a USB audio adapter which is commonly used and tested the audio with it. I attached the link to what I bought below.

USB Audio Adapter - Works with Raspberry Pi

I checked the audio devices and drivers with the same command as before.

cat /proc/asound/cards
 0 [Headphones     ]: bcm2835_headphonbcm2835 Headphones - bcm2835 Headphones
                      bcm2835 Headphones
 1 [Device         ]: USB-Audio - USB PnP Sound Device
                      C-Media Electronics Inc. USB PnP Sound Device at usb-3f980000.usb-1.1.3, full s
 2 [vc4hdmi        ]: vc4-hdmi - vc4-hdmi
                      vc4-hdmi

aplay -L
default
    Playback/recording through the PulseAudio sound server
null
    Discard all samples (playback) or generate zero samples (capture)
jack
    JACK Audio Connection Kit
...
usbstream:CARD=Device
    USB PnP Sound Device
    USB Stream Output
...

cat /proc/asound/modules
 0 snd_bcm2835
 1 snd_usb_audio
 2 (efault)

Judging from the outputs, the same driver was used as PlayStation Eye, and the audio adapter was detected as an audio device properly. Then I tried the speaker test command. But I couldn’t hear anything. So I thought this problem came from anything other than devices and drivers because the adapter was used widely and shouldn't have been needed to configure.

At the same time, I got a huge clue to solve this problem, which is that the adapter was flashing when I ran the speaker test command. I didn’t know the specifications before I bought it but luckily the flashing feedback gave me confirmation that it was working. So I thought the volume might be too small to listen.

I increased the volume with alsamixer command like the following link.

Audio Troubleshooting

Then I run the speaker test command again. Finally, I could hear the sounds from the adapter and the PlayStation Eye. The cause was quite simple and easy but it took a few weeks to solve.

That’s it!