Re: static noise USB Microphone AKG Perception 120 USB

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Am Freitag, 26. September 2014, 14:21:28 schrieb Sven Moeller:
> Hello List,
> 
> recently I've bought this Mic. The AKG Perception 120 USB has a 24 bit A/D
> converter with 128x oversampling. But alsa recognizes just 16bit. When I do
> record "just silence" I get a white noise. In the alsamixer I set the
> volume of the Mic to ~43%. On the vu-meter arecord shows nothing. But
> Audacity shows amplitudes on the vu-meter. I was trying to force the 24bit
> support by unloading the usb-snd-audio module, unplugging the mic and
> loading the module by hand like this:
> 
> modprobe usb-snd-audio device_setup=0x09
> 
> After plugging in the mic nothing has changed. arecord --dump-hw-params -D
> hw:USB reports just the same sample format 16bit little endian instead of a
> 24bit format.
> 
> Is this "just" an issue with the initalization of the microphone? Or is it
> not supported by the driver completely?
> 
> I did test this on my PC (ARCH-Linux, AMD Opteron 1356 QuadCore, 8GB RAM,
> Foxcon DigitialLife Mainboard). I did the test on my WeTab (Manjaro with
> Netbook Optimized Kernel 3.12) also with the same result.
> 
> 
> Any suggestions how to get rid of this static white noise?
> 
> thx & kind regards
> 
> Sven

So, here's the technical point of view:

1. sudo modprobe snd-usb-audio index=1 device_setup=0x09

2. microphone pluged in.

3. 
[  271.572941] usbcore: registered new interface driver snd-usb-audio
[  293.114507] usb 5-2: new full-speed USB device number 2 using ohci-pci
[  293.294760] usb 5-2: current rate 0 is different from the runtime rate 48000
[  293.300760] usb 5-2: current rate 0 is different from the runtime rate 48000
[  770.206791] usb 5-2: current rate 8000 is different from the runtime rate 
48000

4. 
**** List of CAPTURE Hardware Devices ****
card 0: SB [HDA ATI SB], device 0: ALC1200 Analog [ALC1200 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: SB [HDA ATI SB], device 2: ALC1200 Alt Analog [ALC1200 Alt Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: USB [AKG Perception 120 USB], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0


5.
arecord --dump-hw-params -D hw:USB
Recording WAVE 'stdin' : Unsigned 8 bit, Rate 8000 Hz, Mono
HW Params of device "hw:USB":
--------------------
ACCESS:  MMAP_INTERLEAVED RW_INTERLEAVED
FORMAT:  S8 S16_LE
SUBFORMAT:  STD
SAMPLE_BITS: [8 16]
FRAME_BITS: [8 32]
CHANNELS: [1 2]
RATE: [6400 48000]
PERIOD_TIME: [1000 81920000]
PERIOD_SIZE: [16 524288]
PERIOD_BYTES: [64 524288]
PERIODS: [2 1024]
BUFFER_TIME: (666 163840000]
BUFFER_SIZE: [32 1048576]
BUFFER_BYTES: [64 1048576]
TICK_TIME: ALL
--------------------
arecord: set_params:1233: Sample format non available
Available formats:
- S8
- S16_LE

Here at "Available formats" I do expect kinda 24bit format. But nothing. If I 
execute arecord --dump-hw-params -D plughw:USB I get this output:

Recording WAVE 'stdin' : Unsigned 8 bit, Rate 8000 Hz, Mono
HW Params of device "plughw:USB":
--------------------
ACCESS:  MMAP_INTERLEAVED MMAP_NONINTERLEAVED MMAP_COMPLEX RW_INTERLEAVED 
RW_NONINTERLEAVED
FORMAT:  S8 U8 S16_LE S16_BE U16_LE U16_BE S24_LE S24_BE U24_LE U24_BE S32_LE 
S32_BE U32_LE U32_BE FLOAT_LE FLOAT_BE FLOAT64_LE FLOAT64_BE MU_LAW A_LAW 
IMA_ADPCM S24_3LE S24_3BE U24_3LE U24_3BE S20_3LE S20_3BE U20_3LE U20_3BE 
S18_3LE S18_3BE U18_3LE U18_3BE
SUBFORMAT:  STD
SAMPLE_BITS: [4 64]
FRAME_BITS: [4 640000]
CHANNELS: [1 10000]
RATE: [4000 4294967295]
PERIOD_TIME: [1000 81920000]
PERIOD_SIZE: [4 4294967295]
PERIOD_BYTES: [2 4294967295]
PERIODS: (0 1073741824)
BUFFER_TIME: [1 4294967295]
BUFFER_SIZE: [2 4294967294]
BUFFER_BYTES: [1 4294967295]
TICK_TIME: ALL
--------------------
RIFF$�WAVEfmt @data���������~��~���~���������~���~~���~�~��^CAborted by signal 
Interrupt...
arecord: pcm_read:2031: read error: Interrupted system call
hit <ctrl>+<c>

Huh? What's the difference bitween -D hw:usb and -D plughw:USB in this case? Is 
the line starting with @data captured data by the mic? Is arecord not able to 
determine supported formats? Maybe this is something for the Devs?

Sven

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