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doc:appunti:linux:audio:audio_recording [2019/04/23 10:23]
niccolo [Wireless UHF microphone on Android]
doc:appunti:linux:audio:audio_recording [2019/05/22 15:51] (current)
niccolo [Electrical compatibility and hardware autodetection]
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 Despite all this empirical approach, the **voice registration is quite satisfying**! Despite all this empirical approach, the **voice registration is quite satisfying**!
-===== Wireless ​UHF microphone ​on Android =====+====== Audio Recording With 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**! 
 + 
 +We can group the problems you can face in three main categories:​ 
 + 
 +  * Physical connection 
 +  * Electrical compatibility and hardware autodetection 
 +  * Software capabilities and settings 
 + 
 +===== Physical connection ===== 
 + 
 +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** FIXME 
 + 
 +===== Software capabilities and settings ​===== 
 + 
 +FIXME Complete the article!
  
 Wishing to connect the **UHF microphone** to an **Android smartphone**,​ we prepared an **adapter cable**. From 3.5 mm jack TRRS male to 1/4" jack TS female, with this pinout: Wishing to connect the **UHF microphone** to an **Android smartphone**,​ we prepared an **adapter cable**. From 3.5 mm jack TRRS male to 1/4" jack TS female, with this pinout:
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   * [[https://​forum.xda-developers.com/​showthread.php?​t=2072612|External Mic on Galaxy Devices]]   * [[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://​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.1556007823.txt.gz · Last modified: 2019/04/23 10:23 by niccolo