On Sun, 04 Oct 2020 18:22:43 +0200, info wrote: > > Hi all, > > > I am writing a program that aims to auto-discover the microphone > device that the user is speaking into. I started off by querying > device hints and collected all devices with the IO types of null, > since I have not found any devices with the type of Input. I am > puzzled how it is possible that there is no Input, where a microphone > device should not be able to emit sound. This is the list on my > particular machine: > > Name of device: sysdefault:CARD=SB > Description of device: HDA ATI SB, ALC892 Analog > Default Audio Device > I/O type of device: (null) > > Name of device: front:CARD=SB,DEV=0 > Description of device: HDA ATI SB, ALC892 Analog > Front speakers > I/O type of device: (null) > > Name of device: surround21:CARD=SB,DEV=0 > Description of device: HDA ATI SB, ALC892 Analog > 2.1 Surround output to Front and Subwoofer speakers > I/O type of device: Output > > Name of device: surround41:CARD=SB,DEV=0 > Description of device: HDA ATI SB, ALC892 Analog > 4.1 Surround output to Front, Rear and Subwoofer speakers > I/O type of device: Output > > Name of device: surround50:CARD=SB,DEV=0 > Description of device: HDA ATI SB, ALC892 Analog > 5.0 Surround output to Front, Center and Rear speakers > I/O type of device: Output > > Name of device: surround71:CARD=SB,DEV=0 > Description of device: HDA ATI SB, ALC892 Analog > 7.1 Surround output to Front, Center, Side, Rear and Woofer speakers > I/O type of device: Output > > Name of device: sysdefault:CARD=SB > Description of device: HDA ATI SB, ALC892 Analog > Default Audio Device > I/O type of device: (null) > > Name of device: front:CARD=SB,DEV=0 > Description of device: HDA ATI SB, ALC892 Analog > Front speakers > I/O type of device: (null) > > Now, I am more puzzled, because none of them is a microphone device > explicitly. How can my program determine which of them is actually a > microphone? > > Also, why are devices are duplicated in the output from > snd_device_name_hint()? The very first device is also repeated as the > 2nd last one... Apart from the lack of the Input direction (maybe a bug in the hint code), the fundamental problem is that the driver cannot tell always the device type at all for each PCM stream. It's simply because a stream may give you any input type depending on the mixer route; it's the case of HD-audio. So, the same PCM device may be a mic, or a headset mic, or a line-in, or whatever. Sometimes there are dedicated PCM devices for certain inputs, but most of the PCM streams are generic purpose. Takashi
