Differences

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--- doc:appunti:linux:audio:audio_recording [2019/04/23 11:05] – [Wireless UHF microphone on Android] niccolo
+++ doc:appunti:linux:audio:audio_recording [2019/04/23 12:52] – [Web References] niccolo
@@ Line 169: / Line 169: @@
 Despite all this empirical approach, the **voice registration is quite satisfying**!
-===== Audio Recording With 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**!
+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 fece in three main categories:
+We can group the problems you can face in three main categories:
   * Physical connection
-  * Hardware autodetection
+  * 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**.
+FIXME: How much current is provided in our test? Is the current always present or switched-on only at jack insertion?
+Another parameter which should be considered is the **impedence** FIXME
+===== Software capabilities and settings =====
 FIXME Complete the article!
@@ Line 199: / Line 215: @@
   * [[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]]