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--- doc:appunti:linux:audio:audio_recording [2020/12/28 16:39] – [Ugreen USB audio adapter] niccolo
+++ doc:appunti:linux:audio:audio_recording [2020/12/28 17:14] – [Wireless mic on Ugreen USB audio adapter] niccolo
@@ Line 125: / Line 125: @@
 See this article about **[[audio_recording_android]]**.
-====== Wireless mic on Ugreen USB audio adapter ======
+===== Wireless mic on Ugreen USB audio adapter =====
 The device is detected by the Linux Kernel 4.9.0 in this way:
@@ Line 143: / Line 143: @@
 {{ ugreen-usb-audio.jpg?direct&220|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.
 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**.
@@ Line 150: / Line 152: @@
 {{usb-advanced-audio-device-alsamixer.png?direct&300|USB Advenced Audio Device in Alsamixer}}
-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.
+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**).
+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**.
 ===== Web References =====