USB mic works with ALSA `arecord`, but not with wurb2020

[slowglow]

Hi,

I was tryng different not officially supported USB microphones. Unsurprisingly, they didn't work. They were, however, visible in alsamixer and did work with arecord. So, first my question is, what is the benefit provided by pyalsaaudio over direct calls to command line utility arecord?

After some fiddling around, I realized that one of my mics provides 32-bit floating number stream, which is suported by ALSA and arecord, but it seems that wurb2020 has the int16 type hard-coded. How hard would it be to make the changes to support mics with output different from int16?

Cheers

[arnoldandreasson]

Hi slowglow, I have used other microphones too, but all of them can deliver a 16 bits data stream when ALSA asks for it. 12 bits, like what the AudioMoth can deliver, is good enough and you will not need more than 16 bits. Strange if a 32 bits mic can't deliver 16 bits. I will not add support for 32 bits in current version, maybe in a future version 1.0, if it is needed for some reason. If you check the code for the pathfinder detector there is a better designed sond capture module with stereo support, and that one may be used in a future version 1.0 detector. I hope you noticed the possibility to specify a part of the mics id string in "wurb_rec_start.sh" and don't need to hack the code. What mic are you using? For example HiFiBerry DAC+ ADC works for me.

[slowglow]

Thanks for commenting. I will take a look at the pathfinder detector code. Multi-channel support is really interesting to me. For the time being, I am trying to track down where the current wurb2020 code is failing, but I do not see any error messages when I ssh into the raspberry pi console and run bash /home/pi/cloudedbats_wurb_2020/wurb_rec_start.sh manually. It starts the uvicorn server, but no files are written. I have set the WURB_REC_INPUT_DEVICE and WURB_REC_INPUT_DEVICE_FREQ_HZ in wurb_rec_start.sh. (Thanks for this change, it was very helpful). If you can tell me where to insert the breakpoints, I will try to look around and debug. Regarding the hardware, here is what I get from ALSA with -D hw option (access the hardware device directly):

arecord -D hw:1,0 --dump-hw-params -d1 > /dev/null

Output:

Recording WAVE 'stdin' : Unsigned 8 bit, Rate 8000 Hz, Mono
HW Params of device "hw:1,0":
--------------------
ACCESS:  MMAP_INTERLEAVED RW_INTERLEAVED
FORMAT:  S32_LE
SUBFORMAT:  STD
SAMPLE_BITS: 32
FRAME_BITS: 128
CHANNELS: 4
RATE: [44100 192000]
PERIOD_TIME: [125 743039)
PERIOD_SIZE: [6 32768]
PERIOD_BYTES: [96 524288]
PERIODS: [2 1024]
BUFFER_TIME: (62 1486078)
BUFFER_SIZE: [12 65536]
BUFFER_BYTES: [192 1048576]
TICK_TIME: ALL
--------------------
arecord: set_params:1343: Sample format non available
Available formats:
- S32_LE

And here is what I get from ALSA with -D plughw option (inserts sample rate and format conversion plugins, if needed):

arecord -D plughw:1,0 --dump-hw-params -d1 > /dev/null

Output:

Recording WAVE 'stdin' : Unsigned 8 bit, Rate 8000 Hz, Mono
HW Params of device "plughw:1,0":
--------------------
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 S20_LE S20_BE U20_LE U20_BE 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: [125 743039)
PERIOD_SIZE: (0 3191328204)
PERIOD_BYTES: (0 4294967295)
PERIODS: (0 4294967295]
BUFFER_TIME: [1 4294967295]
BUFFER_SIZE: [1 4294967294]
BUFFER_BYTES: [1 4294967295]
TICK_TIME: ALL
--------------------

[sail2themoon]

Hi, well it's hard-coded, but it's a one-liner :) I had the same problem with a USB mic, that can record 16 bits and 24 bits at 192KHz fine using arecord - but: When recording 16bits with that mic with arecord, it's actually converted from 24 to 16 bits. You can see this, while adding arecords option "-v". Wurb-recordings where just loud noise. I've changed the line 597 of wurb_recorder.py from: self.wave_file.setsampwidth(2) # 2=16 bits.

to: self.wave_file.setsampwidth(3) # 2=16 bits, 3=24bits, 4=32bits

now I have proper recordings, even in 24 bits - that's fantastic! :)

I've also tested 32 bits, which gave me 32 bit wave files, but noise again. My mic can only do 24 bits.

Here some info about my mic via "more /proc/asound/card1/stream0": Capture: Status: Running Interface = 1 Altset = 1 Packet Size = 600 Momentary freq = 192000 Hz (0xc0.0000) Interface 1 Altset 1 Format: S24_3LE Channels: 1 Endpoint: 0x82 (2 IN) (ASYNC) Rates: 48000, 44100, 192000, 96000 Bits: 24 Channel map: MONO

[arnoldandreasson]

Thank's sail2themoon for your comments. In the next major release I'm planning for a YAML-based configuration file with optional support for various mics. Your tests indicates that there is an automatic conversion from 24 to 16 bits, witch is great but I have to dig deeper into that. What kind of mics "can only do 24 bits"? 32 bits is easier to handle than 24 bits, but I have no code for that now. Also stereo support is in the pipeline.

[sail2themoon]

sounds great! The conversion is only done with Alsa/arecord, if an input device can't handle a specific bit-rate or bit-width. This can look like the input device is actually capable of it. I don't think Wurb does any conversion, because my mic just put out noise with 16bit. That was when I discovered, that arecord does conversion.

My mic is one of the cheapest 192KHz-USB-mics from "Jeemak", with a modified microphone capsule by myself - but: I think the 192KHz are fake: I get really strange recordings above ~50KHz, seen in the spectrogram.