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doc:appunti:linux:audio:audio_recording [2020/12/28 17:13] – [Wireless mic on Ugreen USB audio adapter] niccolodoc:appunti:linux:audio:audio_recording [2020/12/28 18:22] (current) niccolo
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 Unlike capacitor ones, electret microphones **do not require polarizing voltage**, but generally they contain an integrated preamplifier that **does require power**. In this cases a **TRS jack** can be used, where the ring carries power via a resistor from, normally, a 5 V supply in the computer (often incorrectly called //polarizing power// or //bias//). Generally these microphones built to be plugged into computers and electronic audio devices, have a **TRS 3.5 mm jack**, carrying the mic signal and the required current. Unlike capacitor ones, electret microphones **do not require polarizing voltage**, but generally they contain an integrated preamplifier that **does require power**. In this cases a **TRS jack** can be used, where the ring carries power via a resistor from, normally, a 5 V supply in the computer (often incorrectly called //polarizing power// or //bias//). Generally these microphones built to be plugged into computers and electronic audio devices, have a **TRS 3.5 mm jack**, carrying the mic signal and the required current.
- 
-====== Problem: silence gaps using a cheap USB dongle ====== 
- 
-I was **unable to use the microphone connector** on my Acer TravelMate, so I tried to use an USB dongle, marked **LinQ**. The device was detected by the Linux Kernel 4.9.0: 
- 
-<code> 
-usb 2-1.3: new full-speed USB device number 9 using ehci-pci 
-usb 2-1.3: New USB device found, idVendor=0c76, idProduct=1607 
-usb 2-1.3: New USB device strings: Mfr=0, Product=1, SerialNumber=0 
-usb 2-1.3: Product: USB Headphone Set 
-input: USB Headphone Set as /devices/pci0000:00/0000:00:1d.0 
-    /usb2/2-1/2-1.3/2-1.3:1.3/0003:0C76:1607.0004/input/input92 
-hid-generic 0003:0C76:1607.0004: 
-    input,hidraw2: USB HID v1.00 Device [USB Headphone Set] 
-    on usb-0000:00:1d.0-1.3/input3 
-</code> 
- 
-{{ linq-usb-audio.png?direct&100|LinQ USB audio dongle}} 
-The USB audio adapter worked quite nicely at playing audio, I use it on a QNAP TS-120 NAS, transformed into a media player installing Debian GNU/Linux on it. The Linux kernel and the **ALSA audio subsystem** works well on setting the levels for **playback**. 
- 
-Once started Audacity, I was able to select the microphone line of the USB dongle as a **capture device**: 
- 
-{{audacity-select-usb-audio.png?direct&260|}} 
- 
-Recording a sample track revealed an annoying problem: about **every 0.4 seconds** you can see a **gap of silence** in the audio track of about **two hundredths of a second**. The audio track is unusable! 
- 
-{{audacity-track-gaps.png?direct&400|}} 
  
 ====== Wireless UHF microphone ====== ====== Wireless UHF microphone ======
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 ===== 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:+See this article about **[[audio_recording_usb_adapter]]**. 
 + 
 +====== Problem: silence gaps using a cheap USB dongle ====== 
 + 
 +I was **unable to use the microphone connector** on my Acer TravelMate, so I tried to use an USB dongle, marked **LinQ**. The device was detected by the Linux Kernel 4.9.0:
  
 <code> <code>
-usb 2-1.3: new full-speed USB device number using ehci-pci +usb 2-1.3: new full-speed USB device number using ehci-pci 
-usb 2-1.3: New USB device found, idVendor=0d8c, idProduct=0024 +usb 2-1.3: New USB device found, idVendor=0c76, idProduct=1607 
-usb 2-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=0 +usb 2-1.3: New USB device strings: Mfr=0, Product=1, SerialNumber=0 
-usb 2-1.3: Product: USB Advanced Audio Device +usb 2-1.3: Product: USB Headphone Set 
-usb 2-1.3: Manufacturer: C-Media Electronics Inc. +input: USB Headphone Set as /devices/pci0000:00/0000:00:1d.0 
-input: C-Media Electronics Inc. USB Advanced Audio Device as /devices/pci0000:00/0000:00:1d.0 +    /usb2/2-1/2-1.3/2-1.3:1.3/0003:0C76:1607.0004/input/input92 
-    /usb2/2-1/2-1.3/2-1.3:1.3/0003:0D8C:0024.0004/input/input18 +hid-generic 0003:0C76:1607.0004: 
-hid-generic 0003:0D8C:0024.0004: +    input,hidraw2: USB HID v1.00 Device [USB Headphone Set]
-    input,hidraw2: USB HID v1.11 Device [C-Media Electronics Inc. USB Advanced Audio Device]+
     on usb-0000:00:1d.0-1.3/input3     on usb-0000:00:1d.0-1.3/input3
 </code> </code>
  
-{{ ugreen-usb-audio.jpg?direct&220|Ugreen USB Audio Adapter}}+{{ linq-usb-audio.png?direct&100|LinQ USB audio dongle}} 
 +The USB audio adapter worked quite nicely at playing audio, I use it on a QNAP TS-120 NAS, transformed into a media player installing Debian GNU/Linux on it. The Linux kernel and the **ALSA audio subsystem** works well on setting the levels for **playback**.
  
-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.+Once started Audacity, I was able to select the microphone line of the USB dongle as a **capture device**:
  
-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**.+{{audacity-select-usb-audio.png?direct&260|}}
  
-It seems that the best setting for audio recording through the mic, is to keep the **capture mic gain to 100**:+Recording a sample track revealed an annoying problem: about **every 0.4 seconds** you can see a **gap of silence** in the audio track of about **two hundredths of a second**. The audio track is unusable!
  
-{{usb-advanced-audio-device-alsamixer.png?direct&300|USB Advenced Audio Device in Alsamixer}} +{{audacity-track-gaps.png?direct&400|}}
- +
-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"+
-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 ======
-===== Web References =====+
  
   * [[wp>Microphone]]   * [[wp>Microphone]]
doc/appunti/linux/audio/audio_recording.1609172024.txt.gz · Last modified: 2020/12/28 17:13 by niccolo