When I start Qt’s ‘Audio Example’ that shows the audio amplitude level from the microphone I can’t see any voice samples while speeling into the microphone.
However, I notice some noise and knocking on the headphones speaker produces some peaks on the microphone amplitude.
Hints:
I did not cross the headphone and the microphone connectors.
amixer setup seems OK for capturing from MIC:
Simple mixer control 'Headphone',0
Capabilities: pvolume
Playback channels: Front Left - Front Right
Limits: Playback 0 - 127
Mono:
Front Left: Playback 63 [50%] [-20.00dB]
Front Right: Playback 63 [50%] [-20.00dB]
Simple mixer control 'Headphone Mux',0
Capabilities: enum
Items: 'DAC' 'LINE_IN'
Item0: 'DAC'
Simple mixer control 'Headphone Playback ZC',0
Capabilities: pswitch pswitch-joined
Playback channels: Mono
Mono: Playback [on]
Simple mixer control 'PCM',0
Capabilities: pvolume
Playback channels: Front Left - Front Right
Limits: Playback 0 - 192
Mono:
Front Left: Playback 144 [75%]
Front Right: Playback 144 [75%]
Simple mixer control 'Mic',0
Capabilities: volume volume-joined
Playback channels: Mono
Capture channels: Mono
Limits: 0 - 3
Mono: 2 [67%] [30.00dB]
Simple mixer control 'Capture',0
Capabilities: cvolume
Capture channels: Front Left - Front Right
Limits: Capture 0 - 15
Front Left: Capture 12 [80%]
Front Right: Capture 12 [80%]
Simple mixer control 'Capture Attenuate Switch (-6dB)',0
Capabilities: pswitch pswitch-joined
Playback channels: Mono
Mono: Playback [off]
Simple mixer control 'Capture Mux',0
Capabilities: enum
Items: 'MIC_IN' 'LINE_IN'
Item0: 'MIC_IN'
Simple mixer control 'Capture ZC',0
Capabilities: pswitch pswitch-joined
Playback channels: Mono
Mono: Playback [on]
I think you have two issues with the hardware setup.
The Ixora does not have a biasing circuit, and additonally there is no biasing circuit on the Apalis iMX6 module. (I expect your headset’s microphone to need biasing)
There are at least two common pinouts for 3.5mm headset connectors. On the Ixora the “OMTP” assignment is used, your cable adapter seems to use the “CTIA / AHJ” assignment.
I’m not very familiar with the Boot2Qt software stack, however I would expect that once the above two issues are overcome that audio works. Otherwise Marcel’s suggestion of first bringing up audio with one of our regular images could prove that the audio hardware is working and one has to see how to use alsa with the Boot2Qt image.
Can you provide that part of the schematics?
We don’t give out the schematics of the modules. However I’m sure that there is no way to enable a biasing voltage on the module.
Does it make sense to not connect the BIAS voltage? > If yes, which headset can I use?
Not really, as nowadays nearly all microphones require this. Adding this will be part of the next hardware revision of the Ixora board.