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--- doc:appunti:linux:audio:audio_recording_tmb113_e [2020/12/28 08:39] – created niccolo
+++ doc:appunti:linux:audio:audio_recording_tmb113_e [2020/12/28 17:09] (current) – [Recording with PulseAudio parecord] niccolo
@@ Line 1: / Line 1: @@
-====== Audio recording with the Acer Travelmate TMB113-E ======
+====== Audio recording with the Acer TravelMate TMB113-E ======
-How to record audio using a **wireless microphone** connected to the audio jack of an **Acer Travelmate TMB113-E**, running  **Debian GNU/Linux 10 Buster**. The microphone is a **[[wp>Lavalier_microphone|lavalier]]** one, with an **UHF** (630 MHz) belt transmitter and a receiver monted on a **1/4" TS jack**.
+{{acer-travelmate-wireless-microphone.jpg?480 |Wireless Microphone on the Acer TravelMate}}
+How to record audio using a **wireless microphone** connected to the audio jack of an **Acer TravelMate TMB113-E**, running  **Debian GNU/Linux 10 Buster**.
+The microphone is a **[[wp>Lavalier_microphone|lavalier]]** one, with an **UHF** (630 MHz) belt transmitter and a receiver mounted on a **1/4" TS jack**. I am mainly interested in recording using **command line tools**.
+===== Electrical connection =====
+I used an headset/microphone **split cable** to connect to the **3.5 mm CTIA audio jack** of the Acer TravelMante and a **self-made cable** to adapt the **TRS 3.5 mm** mic jack to the **1/4" TS jack**. The overall pinout is as follow:
+^ 1/4" TS female jack  ^ Signal         ^ 3.5 mm TRRS male jack (CTIA)  ^
+|                      | Not connected  | **Tip**                       |
+|                      | Not connected  | **Ring**                      |
+| **Sleeve**           | Ground         | **Ring**                      |
+| **Tip**              | Microphone     | **Sleeve**                    |
+===== Problem detecting the external microphone =====
 At first try 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), when you plug and unplug the split cable you can see this output:
@@ Line 65: / Line 80: @@
 The **pincfg** hex values are shown on stdout by hdajackretask when you press the //Apply now// button, so you can take note and build different files for different scenarios to use during bootstrap. For the TBM113-E the normal status of **pin 0x19** corresponds to the value **0x411111f0**, whereas the override status (plugged microphone) is **0x03a19020**.
-I used the PulseAudio mixer **pavucontrol** to set the recording volume level: it turned out that a value of **16463** (corresponding to 25% of the slider, or -36.00 dB) is the best setting for normal speach. At the ALSA level (lower level interface used by PylseAudio) it means a **Capture** level of **100** and a **Mic Boost** of **0**. This is a table of value correspondence between PulseAudio and ALSA:
+When you apply the pin override in **hdajackretask**, it is not clear **how to disable the external microphone**: re-setting **Pin 0x19** to **Not connected** does not generate the ACPI microphone unplug event, and the bias current is not cleared. The bias power disappears from the jack after a poweroff or an hybernation, so the external microphone seems to be "unplugged" after these events.
+If instead the override is made at bootstrap via the modules patch option, the settings survive after the hibernation: you can see the **jack/microphone MICROPHONE plug** ACPI event after the resume.
+===== Setting the recording volume with PulseAudio =====
+I used the PulseAudio mixer **pavucontrol** to set the recording volume level: it turned out that a value of **16463** (corresponding to 25% of the slider, or -36.00 dB) is the best setting for normal speach. At the ALSA level (lower level interface used by PulseAudio) it means a **Capture** level of **100** and a **Mic Boost** of **0**. This is a table of value correspondence between PulseAudio and ALSA (notice that it is specific to this PCI sound card):
 ^ ALSA                      ^ PulseAudio                        ^
@@ Line 72: / Line 93: @@
 | Capture 100, Mic Boost 51 | Volume: 41353 /  63% / -12.00 dB  |
-When you apply the pin override in **hdajackretask**, it is not clear **how to disable the external microphone**: re-setting **Pin 0x19** to **Not connected** does not generate the ACPI microphone unplug event, and the bias current is not cleared. The bias power disappears from the jack after a poweroff or an hybernation, so the external microphone seems to be "unplugged" after these events.
+You can check the correspondence between **PulseAudio** and **ALSA** levels by executing **alsamixer**, **pavucontrol** and **pacmd list-sources** commands. The settings you make in PulseAudio will be reflected in ALSA, and vice-versa.
-If instead the override is made at bootstrap via the modules patch option, the settings survive after the hibernation: you can see the **jack/microphone MICROPHONE plug** ACPI event after the resume.
+===== Recording with PulseAudio parecord =====
+I want to use the **PulseAudio** subsystem to record the audio; I don't want to use the ALSA kernel-level interface, which needs direct and exclusive access to the device.
+Using the command **pacmd list-sources** you can discover the **name** of the **device.class** of type **sound**, the current **volume** level, the **base volume** and the **ports** (microphones) availables.
+The recording volume should be a vaule between the **base volume** and **65536** (corresponding to 100%, or 0.00 dB). Every different hardware should be tested to find the best settings to get a clear and loud sound, but to avoid clipping (out of scale samples).
+<code>
+pacmd list-sources
+source(s) available.
+    index: 0
+        name: <alsa_output.pci-0000_00_1b.0.analog-stereo.monitor>
+        ...
+        properties:
+                device.description = "Monitor of Built-in Audio Analog Stereo"
+                device.class = "monitor"
+                ...
+  * index: 1
+        name: <alsa_input.pci-0000_00_1b.0.analog-stereo>
+        volume: front-left: 26092 /  40% / -24.00 dB,   front-right: 26092 /  40% / -24.00 dB
+        base volume: 5206 /   8% / -66.00 dB
+        ...
+        properties:
+                device.class = "sound"
+                ...
+        ports:
+                analog-input-internal-mic: Internal Microphone (priority 8900, available: no)
+                ...
+                analog-input-mic: Microphone (priority 8700, available: yes)
+        active port: <analog-input-mic>
+</code>
+**Beware** that with the audio card of the TMB113-E, the port **analog-input-mic** refers to the external microphone when that one is connected (or forcibly connected by hdajackretask), but the same name refers to the internal microphone when the audio jack is disconnected. In fact the **analog-input-internal-mic** only exists if there are two microphone ports.
+Once you understand the output of **pacmd list-sources**, it is very simple to activate the recording using a command line script:
+<code bash>
+#!/bin/sh
+SOURCE='alsa_input.pci-0000_00_1b.0.analog-stereo'
+PORT='analog-input-mic'
+VOLUME=16463
+pacmd set-default-source "$SOURCE"
+pacmd set-source-port "$SOURCE" "$PORT"
+pacmd set-source-volume "$SOURCE" "$VOLUME"
+pacmd set-source-mute "$SOURCE" 0
+parecord --verbose --device="$SOURCE" --channels=1 --fix-rate foobar.wav
+</code>
+The result is a **44100 Hz, 16 bit little-endian, mono** audio file, quite satisfactory for quality and low background noise.
+===== Microphone plug/unplug events =====
 Having set the pin 19 forcibly to microphone, I often noticed that microphone plug/unplug **events are reported continously** (about every 3 seconds) by the ACPI subsystem: