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--- doc:appunti:linux:audio:audio_recording [2019/04/09 11:59] – [Electret] niccolo
+++ doc:appunti:linux:audio:audio_recording [2020/12/28 17:14] – [Wireless mic on Ugreen USB audio adapter] niccolo
@@ Line 1: / Line 1: @@
-====== Audio Recording With Linux ======
+====== Audio Recording With GNU/Linux ======
 ===== Choosing the right jack =====
@@ Line 44: / Line 44: @@
 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 ====
@@ Line 56: / Line 57: @@
 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:
+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>
-jack/headphone HEADPHONE plug
+usb 2-1.3: new full-speed USB device number 9 using ehci-pci
-jack/headphone HEADPHONE unplug
+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>
-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**:
+{{ 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**.
-  * Enable the **Show unconnected pins** option.
+Once started Audacity, I was able to select the microphone line of the USB dongle as a **capture device**:
-  * 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:
+{{audacity-select-usb-audio.png?direct&260|}}
-<code>
+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!
-jack/microphone MICROPHONE plug
-</code>
+{{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]]**.
-Now you can also measure a **bias current of 2.85 V** between the ground (**sleeve**) and the **ring** or the **tip**.
+===== Wireless mic on Android =====
-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?
+See this article about **[[audio_recording_android]]**.
-===== Wireless microphone =====
-===== 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 100: / 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**.
-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.
+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}}
-===== Problem: silence gaps using a cheap USB dongle =====
+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**).
-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:
+Here are the commands to start an audio recording using a shell script:
-<code>
+<code bash>
-usb 2-1.3: new full-speed USB device number 9 using ehci-pci
+#!/bin/sh
-usb 2-1.3: New USB device found, idVendor=0c76, idProduct=1607
+SOURCE='alsa_input.usb-C-Media_Electronics_Inc._USB_Advanced_Audio_Device-00.analog-stereo'
-usb 2-1.3: New USB device strings: Mfr=0, Product=1, SerialNumber=0
+PORT='analog-input-mic'
-usb 2-1.3: Product: USB Headphone Set
+VOLUME=65536
-input: USB Headphone Set as /devices/pci0000:00/0000:00:1d.0
+pacmd set-default-source "$SOURCE"
-    /usb2/2-1/2-1.3/2-1.3:1.3/0003:0C76:1607.0004/input/input92
+pacmd set-source-port "$SOURCE" "$PORT"
-hid-generic 0003:0C76:1607.0004:
+pacmd set-source-volume "$SOURCE" "$VOLUME"
-    input,hidraw2: USB HID v1.00 Device [USB Headphone Set]
+pacmd set-source-mute "$SOURCE" 0
-    on usb-0000:00:1d.0-1.3/input3
+parecord --verbose --device="$SOURCE" --channels=1 --fix-rate foobar.wav
 </code>
-{{ linq-usb-audio.png?direct&100|LinQ USB audio dongle}}
+**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**.
-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|}}
 ===== Web References =====
@@ Line 140: / Line 176: @@
   * [[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]]
+  * [[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]]