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using a Raspberry Pi 4 as a USB DSP-DAC
using a Raspberry Pi 4 as a USB DSP-DAC
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Old 10th September 2019, 06:16 PM   #91
CharlieLaub is offline CharlieLaub  United States
diyAudio Member
Join Date: Mar 2007
Location: Michigan
Originally Posted by JukkaM View Post
Okey, here's an update.

I found a script called alsa-capabilities and it reported the following for my dac:
 1) USB Audio Class Digital alsa audio output interface `hw:1,0'
 - device name       = Audio
 - interface name    = USB Audio
 - usb audio class   = 2 - isochronous asynchronous
 - character device  = /dev/snd/pcmC1D0p
 - encoding formats  = S24_3LE
 - monitor file      = /proc/asound/card1/pcm0p/sub0/hw_params
 - stream file       = /proc/asound/card1/stream0
If I put "S24_3LE" to the Pi script, it will print "action: gstreamer pipeline launched at 09/10/19 18:57:22" in a loop and no sound. Reverted back to "S24LE".

Using lower than "96000" in sample rate results in "slowmotion" playback. This is the same wheter I put any default sample rate into settings of the Windows default playback device (mobo integrated soundcard). I restarted the Windows script in between and made no changes to it. Again no difference between "plughw:" and "hw:" prefixed audio devices. If I set Windows playback rate to any and pi rate 96k, the pace of the music normal, but original no bass, pan to right problems are still in effect. Maybe the Windows configs are not correct/don't change as they should?
The loop is Gstreamer failing because you tell it to use a format that is not known, and the script restarting it over and over. Gstreamer does not know the format "S24_3LE". Like I explained above, you must use the Gstreamer equivalent of S24LE in the Pi script.

You can check the supported sample rates for your DAC by typing:
aplay -D hw:1,0 --dump-hw-params /dev/zero
You will see info about supported rates and formats. Please post the output here.

What playback device is the default one under Windows? What is the format you selected for it? This video has an example of how to select the playback format:
If the playback software can change the sample rate and audio format, perhaps to the native format of the file to be bit perfect, the audio will not sound correct.

Please, on your Windows machine, install VB-Cable and configure that as your default playback device. See:
VB-Audio Virtual Apps
Set both recording and playback of VB-Cable to the one you want (e.g. 24/96).

Also, plughw: allows ALSA to resample or reformat the audio that is being sent to the DAC by Gstreamer. That's is not needed, or wanted. I would instead stream in a format that the DAC already supports and use hw: instead.
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