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doc:appunti:linux:audio:audio_recording [2019/04/09 11:58] – [Electret] niccolodoc:appunti:linux:audio:audio_recording [2020/12/28 17:20] – [Wireless mic on Ugreen USB audio adapter] niccolo
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-====== Audio Recording With Linux ======+====== Audio Recording With GNU/Linux ======
  
 ===== Choosing the right jack ===== ===== Choosing the right jack =====
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 A small movable **induction coil**, positioned in the **magnetic field** of a permanent magnet, is attached to the diaphragm. The sound wave moves the diaphragm and the coil moves in the magnetic field, producing a varying current in the coil through **electromagnetic induction**. No power is required: the current is carried directly on **two poles** to the mic input. These microphones generally have a **1/4" mono jack**. A small movable **induction coil**, positioned in the **magnetic field** of a permanent magnet, is attached to the diaphragm. The sound wave moves the diaphragm and the coil moves in the magnetic field, producing a varying current in the coil through **electromagnetic induction**. No power is required: the current is carried directly on **two poles** to the mic input. These microphones generally have a **1/4" mono jack**.
 +
 ==== Condenser ==== ==== Condenser ====
  
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 ==== Electret ==== ==== Electret ====
  
-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 bias 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.
  
-===== External mic on the Acer Travelmate B113-E ===== +====== Problem: silence gaps using a cheap USB dongle ======
- +
-Running **Debian GNU/Linux 9 Stretch**, it seems that the use of the **headphone/microphone split cable** does not abilitate the use of the microphone. In fac, if you run the **acpi_listen** tool (from the **acpid** Debian package), you can see when you insert the split cable: +
- +
-<code> +
-jack/headphone HEADPHONE plug +
-jack/headphone HEADPHONE unplug +
-</code> +
- +
-but nothing is reported about the plug of a microphone. Beside that, no bias current appear on the microphone jack. The solution is to run the **hdajackretask** tool (from the **alsa-tools-gui** Debian package), then force the connection of **Pin 0x19**: +
- +
-  * Enable the **Show unconnected pins** option. +
-  * Click **Pin ID: 0x19** => **Override** => **Microphone**. +
-  * **Apply now** (it asks for the root password, as it has to run a script with superuser privileges). +
- +
-the running **acpi_listen** will print: +
- +
-<code> +
-jack/microphone MICROPHONE plug +
-</code> +
- +
-Now you can also measure a **bias current of 2.85 V** between the ground (**sleeve**) and the **ring** or the **tip**. +
- +
-Is not clear **how to disable the external microphone**: even setting **Pin 0x19** to **Not connected** does not generate the ACPI microphone unplug event, and the bias current is not cleared. FIXME May be after a reboot? +
-===== Wireless microphone ===== +
- +
-===== Ugreen USB audio adapter ===== +
- +
-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> +
- +
-{{ ugreen-usb-audio.jpg?direct&220|Ugreen USB Audio Adapter}} +
- +
-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**. +
- +
-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. +
- +
- +
-===== 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: 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:
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 {{audacity-track-gaps.png?direct&400|}} {{audacity-track-gaps.png?direct&400|}}
 +
 +====== Wireless UHF microphone ======
 +
 +We have purchased an **UHF wireless microphone** on Aliexpress.com for about 25 €. It is composed by:
 +
 +  * The **transmitter** powered by **two AA batteries**, featuring:
 +    * A **[[wp>Lavalier microphone|lavalier microphone]]** on a clip.
 +    * One small **wire-antenna**.
 +    * Frequency range: **610-675 MHz** (53 channels spaced by 1.25 MHz each).
 +    * Modulation system: DQPSK
 +    * Frequency response: 60-16000 Hz
 +    * Transmitted power: 10 dBm
 +    * Working current: %%<=%% 100 mA
 +
 +  * The **receiver** powered by **two AAA batteries**, featuring:
 +    * A 1/4" (6.35 mm) mono jack.
 +    * One small **telescopic antenna**.
 +    * Receiving sensitivity: -94 dBm
 +    * Working current: %%<=%% 100 mA
 +
 +{{wireless-mic-trasmitter.jpg?direct&240|}}
 +{{wireless-mic-receiver.jpg?direct&240|}}
 +
 +To connect the **UHF receiver** to the **Ugreen USB audio adapter**, we built an adapter cable with this pinout:
 +
 +^ 1/4" TS female jack  ^ Signal         ^ 3.5 mm TRS male jack  ^
 +| **Tip**              | Microphone     | **Tip**               |
 +|                      | Not connected  | **Ring**              |
 +| **Sleeve**           | Ground         | **Sleeve**            |
 +
 +The **2.6 volt** current provided by the USB adapter on th **jack ring** will go nowhere (not connected). The **2.6 volt** current provided on the **jack tip** is probably not required by the UHF receiver, but **it should not harm**. **No infromation** is available about **microphone impedence** expected by the USB adapter, on the other hand no information is available about the **impedence of the mic interface** of the UHF receiver.
 +
 +Despite all this empirical approach, the **voice registration is quite satisfying**! See below about connecting the microphone to an Acer TravelMate notebook an to an Android smartphone.
 +
 +===== Wireless mic on the Acer Travelmate TMB113-E =====
 +
 +See this article about **[[audio_recording_tmb113_e]]**.
 +
 +===== Wireless mic on Android =====
 +
 +See this article about **[[audio_recording_android]]**.
 +
 +===== Wireless mic on Ugreen USB audio adapter =====
 +
 +See this article about **[[audio_recording_usb_adapter]]**.
  
 ===== Web References ===== ===== Web References =====
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   * [[http://www.shure.com/americas/support/find-an-answer/will-bias-voltage-from-a-computer-effect-a-dynamic-microphone|Will bias voltage from a computer effect a dynamic microphone?]]   * [[http://www.shure.com/americas/support/find-an-answer/will-bias-voltage-from-a-computer-effect-a-dynamic-microphone|Will bias voltage from a computer effect a dynamic microphone?]]
   * [[http://www.epanorama.net/circuits/microphone_powering.html|Powering microphones]]   * [[http://www.epanorama.net/circuits/microphone_powering.html|Powering microphones]]
 +  * [[https://forum.xda-developers.com/showthread.php?t=2072612|External Mic on Galaxy Devices]] 
 +  * [[https://stackoverflow.com/questions/19255908/android-forcing-external-microphone-jack-input-3-5mm-to-stay-on|Android: Forcing external microphone (jack input 3.5mm) to stay on]] 
 +  * [[https://forum.xda-developers.com/showthread.php?t=1042051|App that turns off microphone AGC (Auto-Gain Control)?]] 
 +  * [[https://stackoverflow.com/questions/47394634/difference-between-voice-communication-and-mic-in-mediarecorder-audiosource|Difference between VOICE_COMMUNICATION and MIC in MediaRecorder.AudioSource]] 
 +  * [[https://stackoverflow.com/questions/47359587/what-is-the-best-audiosource-setting-for-calls|What is the best audiosource setting for calls?]] 
 +  * [[https://amp.reddit.com/r/androidapps/comments/4wo8sz/app_to_force_android_to_use_external_microphone/|App to force android to use external microphone when one is plugged in]]
doc/appunti/linux/audio/audio_recording.txt · Last modified: 2020/12/28 18:22 by niccolo