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====== Audio recording with wireless mic and USB adapter ======

{{ ugreen-usb-audio.jpg?direct&220|Ugreen USB Audio Adapter}}
We tried and **Ugreen USB audio adapter**.

The **microphone socket** is a **3.5 mm TRS type** (three poles), it provides a bias current of **2.6 V** on both the **tip** and the **ring**, so it is advisable, as reported in the device manual, to **NOT use a simple two poles mono jack** (TS type), because it will short-circuit the bias current on the ring with the ground on the sleeve.

The device is detected by the Linux Kernel 4.9.0 in this way:

<code>
usb 2-1.3: new full-speed USB device number 5 using ehci-pci
usb 2-1.3: New USB device found, idVendor=0d8c, idProduct=0024
usb 2-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=0
usb 2-1.3: Product: USB Advanced Audio Device
usb 2-1.3: Manufacturer: C-Media Electronics Inc.
input: C-Media Electronics Inc. USB Advanced Audio Device as /devices/pci0000:00/0000:00:1d.0
    /usb2/2-1/2-1.3/2-1.3:1.3/0003:0D8C:0024.0004/input/input18
hid-generic 0003:0D8C:0024.0004:
    input,hidraw2: USB HID v1.11 Device [C-Media Electronics Inc. USB Advanced Audio Device]
    on usb-0000:00:1d.0-1.3/input3
</code>



===== Setting volume with ALSA =====

Launching **alsamixer** and hitting F6 you can select the **USB Advanced Audio Device** sound card. Hit F4 to view the only one capture device, i.e. the microphone input line. Press **Space** to enable/disable the **capture** and **Up/Down arrows** to increase/decrease the **gain**.

It seems that the best setting for audio recording through the mic, is to keep the **capture mic gain to 100**:

{{usb-advanced-audio-device-alsamixer.png?direct&300|USB Advenced Audio Device in Alsamixer}}

===== Setting volume with PulseAudio =====

I use the **PulseAudio** subsystem above the ALSA modules (this is the preferred method in modern GNU/Linux distro). In this case the volume is controlled via the graphics app **pavucontrol** or on the command line using the **pacmd** tool. The PulseAudio recording volume level should be between the **base volume** (value **20724**) and the **100%** (value **65536**).

===== Recording audio with PulseAudio =====

Here are the commands to start an audio recording using a shell script:

<code bash>
#!/bin/sh
SOURCE='alsa_input.usb-C-Media_Electronics_Inc._USB_Advanced_Audio_Device-00.analog-stereo'
PORT='analog-input-mic'
VOLUME=65536
pacmd set-default-source "$SOURCE"
pacmd set-source-port "$SOURCE" "$PORT"
pacmd set-source-volume "$SOURCE" "$VOLUME"
pacmd set-source-mute "$SOURCE" 0
parecord --verbose --device="$SOURCE" --channels=1 --fix-rate foobar.wav
</code>

**WARNING**: The audio files produced by this USB adapter **do not cover the entire 16-bit range**; the values returned (converted into float dB) extend from **-0.5** to **+0.5**, i.e. exactly **the half of what expected** (-1.0 to +1.0). Above that values, **the audio is clipped**. You can view this in the pavucontrol monitor: it does not matter how loud you speak into the microphone, the volume meter bar never reaches the full scale. So **it is advisable** eventually to lower the volume (e.g. to **75%** or 50%) to **avoid clipping**, and to proceed with post-processing **software amplification**.