doc:appunti:linux:audio:audio_recording
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doc:appunti:linux:audio:audio_recording [2020/12/28 09:57] – niccolo | doc:appunti:linux:audio:audio_recording [2020/12/28 17:20] – [Wireless mic on Ugreen USB audio adapter] 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 // | 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 // | ||
- | ====== Wireless UHF microphone ====== | + | ====== Problem: silence gaps using a cheap USB dongle |
- | + | ||
- | We have purchased an **UHF wireless microphone** on Aliexpress.com for about 25 €. It is composed by: | + | |
- | + | ||
- | * The **transmitter** powered by **two AA batteries**, | + | |
- | * A **[[wp> | + | |
- | * 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**, | + | |
- | * A 1/4" (6.35 mm) mono jack. | + | |
- | * One small **telescopic antenna**. | + | |
- | * Receiving sensitivity: | + | |
- | * Working current: %%<=%% 100 mA | + | |
- | + | ||
- | {{wireless-mic-trasmitter.jpg? | + | |
- | {{wireless-mic-receiver.jpg? | + | |
- | + | ||
- | 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 | + | |
- | | **Tip** | + | |
- | | | Not connected | + | |
- | | **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**! | + | |
- | + | ||
- | ====== External mic on the Acer Travelmate TMB113-E ====== | + | |
- | + | ||
- | See this article about **[[audio_recording_tmb113_e]]**. | + | |
- | + | ||
- | + | ||
- | ===== 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: | ||
Line 122: | Line 84: | ||
{{audacity-track-gaps.png? | {{audacity-track-gaps.png? | ||
- | ===== Ugreen USB audio adapter | + | ====== Wireless UHF microphone ====== |
- | The device is detected by the Linux Kernel 4.9.0 in this way: | + | We have purchased an **UHF wireless microphone** on Aliexpress.com for about 25 €. It is composed by: |
- | < | + | * The **transmitter** powered by **two AA batteries**, |
- | usb 2-1.3: new full-speed USB device number 5 using ehci-pci | + | * A **[[wp> |
- | usb 2-1.3: New USB device found, idVendor=0d8c, | + | * One small **wire-antenna**. |
- | usb 2-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=0 | + | * Frequency range: **610-675 MHz** (53 channels spaced by 1.25 MHz each). |
- | usb 2-1.3: Product: USB Advanced Audio Device | + | * Modulation system: DQPSK |
- | usb 2-1.3: Manufacturer: | + | |
- | input: C-Media Electronics Inc. USB Advanced Audio Device as / | + | |
- | | + | |
- | hid-generic 0003: | + | |
- | | + | |
- | | + | |
- | </code> | + | |
- | {{ ugreen-usb-audio.jpg? | + | * The **receiver** powered by **two AAA batteries**, |
+ | * A 1/4" (6.35 mm) mono jack. | ||
+ | * One small **telescopic antenna**. | ||
+ | * Receiving sensitivity: | ||
+ | * Working current: %%<=%% 100 mA | ||
- | 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/ | + | {{wireless-mic-trasmitter.jpg? |
+ | {{wireless-mic-receiver.jpg? | ||
- | It seems that the best setting for audio recording through the mic, is to keep the **capture mic gain to 100**: | + | To connect |
- | {{usb-advanced-audio-device-alsamixer.png? | + | ^ 1/4" TS female jack ^ Signal |
+ | | **Tip** | ||
+ | | | Not connected | ||
+ | | **Sleeve** | ||
- | 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** | + | The **2.6 volt** current provided by the USB adapter on th **jack ring** will go nowhere |
- | ====== Audio Recording With Android | + | 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 |
- | Recording audio using an **external microphone** connected to an **Android device** can be a real nightmare. We tried the hard way using a Chinese, no-brand, **wireless UHF microphone**! | + | ===== Wireless mic on the Acer Travelmate TMB113-E ===== |
- | We can group the problems you can face in three main categories: | + | See this article |
- | + | ||
- | * Physical connection | + | |
- | * Electrical compatibility and hardware autodetection | + | |
- | * Software capabilities and settings | + | |
- | + | ||
- | ===== Physical connection ===== | + | |
- | + | ||
- | {{ android-external-mic.jpg? | + | |
- | Most Android devices have a **3.5 mm jack** accepting a **TRRS connector in CTIA standard** and every brand of mobile phones produces **headsets** with their own standard. The vast majority of solutions uses **electret microphones** requiring a **bias current**, but use **some combinations of impedence** to detect the insertion of the microphone and to **handle the headset button** (or buttons). | + | |
- | + | ||
- | So, connecting an external microphone, can be as simple as making a cable that connects the **ring** and the **sleve** of the **CTIA connector** to (respectively) the **ground** and the **microphone line** of the microphone. The hard part is to guess, or empirically try, if the microphone **requires a bias current**, if the Android device is provinding such a current and if the microphone produces a sufficient **output level** (actually a voltage in the order of the millivolts) that can be used by the device. | + | |
- | + | ||
- | ===== Electrical compatibility and hardware autodetection ===== | + | |
- | + | ||
- | As stated above, the first problem is **powering the microphone** itself, because generally we will use an **electret** one. It is a **common practice** to provide the power on the same line of the microphone signal, so **requiring just two wires** for both power (from the device to the mic) and for signal (from the mic to the device). The power, also called //bias current//, is generally in the range of **2.5** to **5.0 volt**. | + | |
- | + | ||
- | On a Xiaomi Mi A1 smartphone, which has a **TRRS 3.5 mm jack, CTIA standard**, we measured a bias current of **2.19 volt** between the microphone (sleeve) and the ground (ring). | + | |
- | + | ||
- | Another parameter which should be considered is the **impedence**, | + | |
- | + | ||
- | ===== Software capabilities and settings ===== | + | |
- | + | ||
- | Wishing to connect the **UHF microphone** to an **Android smartphone**, | + | |
- | + | ||
- | ^ 1/4" TS female jack ^ Signal | + | |
- | | | Not connected | + | |
- | | | Not connected | + | |
- | | **Sleeve** | + | |
- | | **Tip** | + | |
- | The smartphone **did not sensed the microphone**, | + | ===== Wireless |
- | Once completed the electrical connection and acknowledged that **automatic detection of the external microphone does not work**, I decided to use the **[[https:// | + | See this article about **[[audio_recording_android]]**. |
- | + | ||
- | To realize the electrical connection explained in the above table, I used a **mic/ | + | |
- | To record audio I used the **[[https:// | + | ===== Wireless |
- | The resulting recording is quite good: a **48 kHz 16 bits** file with good sound quality and low noise. | + | See this article about **[[audio_recording_usb_adapter]]**. |
===== Web References ===== | ===== Web References ===== |
doc/appunti/linux/audio/audio_recording.txt · Last modified: 2020/12/28 18:22 by niccolo