DAC Displays 32-bit when playing 24-bit file

Core Machine (Operating system/System info/Roon build number)

  • Roon OS Version 1.0 (build 227) stable
  • Intel NUC 10 i7
  • Roon Server Version 1.8 (build 783) stable

Network Details (Including networking gear model/manufacturer and if on WiFi/Ethernet)

  • BT FTTP 1Gbit/s
  • BT SmartHub and BT Disc
  • 5 GHz WIFI connection

Audio Devices (Specify what device you’re using and its connection type - USB/HDMI/etc.)

Playback

  • SMSL M6 Mini DAC
  • USB Connection
  • Raspberry Pi 4B
  • DietPi
  • Roon Bridge Version 1.7 (build 571) stable

Remotes

*MacBook Pro (13-inch, 2020)/Big Sur: Roon Version 1.8 (build 783) stable
*iPhone 8: Roon Version 1.8 (build 783) stable

Description Of Issue

Any 16-bit file plays and the SMSL displays 16-bit (44.1kHz and 48kHz files)
Any 24-bit file, whether Qobuz or Local File, plays and the SMSL displays 32 bit (48kHz, 88.1kHz, 96kHz and 192kHz files)

Why doesn’t it show 32-bit?
Is it Roon Bridge, ALSA or my SMSL M6?

Thanks for your help.

Signal path and SMSL screen for 16-bit:


RAAT Server Log for 16-bit:

 > 04/09 15:28:35 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  GOT [219] {"request":"setup","format":{"sample_type":"pcm","sample_rate":44100,"bits_per_sample":16,"channels":2,"sample_subtype":"none"}}
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] alsa output setup: format is pcm 44100/16/2
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] opening [hw:CARD=M6,DEV=0] 44100/16/2
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] prefer larger samples = 0
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [ALSA] [hw:CARD=M6,DEV=0] using hw pcmformat S16_LE bitspersample 16
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [ALSA] [hw:CARD=M6,DEV=0] Requesting 2 periods
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [ALSA] [hw:CARD=M6,DEV=0] Requesting 1764 frames/buffer (882 frames/period)
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [ALSA] [hw:CARD=M6,DEV=0] Initialized with 2 periods with 882 frames/period and 1764 frames/buffer
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] sched_setscheduler succeeded
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  got output message {"signal_path": [{"alsa_device": {"longname": "SMSL SMSL M6 at usb-0000:01:00.0-1.4, high speed", "id": "M6", "name": "SMSL M6", "usbid": "0d8c:0004", "mixername": "USB Mixer", "dri
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] samples per buf 882 ns per buf 20000000 samplerate 44100
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] 882 samples per buf, 3528 bytes per buf, 3528 bytes per hwbuf
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [output/alsa] [hw:CARD=M6,DEV=0] waiting for device to be ready
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [output/alsa] [hw:CARD=M6,DEV=0] device is ready
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [219] {"message":{"signal_path":[{"type":"output","quality":"lossless","method":"alsa","alsa_device":{"longname":"SMSL SMSL M6 at usb-0000:01:00.0-1.4, high speed","id":"M6","usbid":"0d8c:0004","
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [219] {"audio_port_tcp":44573,"audio_port":0,"clock_port":57178,"status":"Success"}
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  GOT [220] {"request":"stream","stream_id":1043304442,"first_seq":-1,"nak_port":-1,"buffer_size":10,"ready_threshold":0.2}
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [220] {"status":"Buffering"}
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [220] {"status":"Ready"}
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  GOT [221] {"request":"start","min_offset":60884353,"stream_sample":0}
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  Doing ASAP start based on current device clock (min_offset=60884353)
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [220] {"status":"Playing"}
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [221] {"time":48902007184514,"status":"Success"}
>     04/09 15:28:35 Trace: [RAAT::SMSL M6] starting playback: now (48901997142857ns) + ns_per_buf(20000000ns) = 48902017142857ns > 48902007184514ns streamsample=0
>     04/09 15:28:45 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  GOT [222] {"request":"stop"}
>     04/09 15:28:45 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [220] {"status":"Stopped"}
>     04/09 15:28:45 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [222] {"status":"Success"}
>     04/09 15:28:50 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  GOT [223] {"request":"end_stream"}
>     04/09 15:28:50 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [220] {"status":"Ended"}
>     04/09 15:28:50 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [223] {"status":"Success"}
>     04/09 15:28:50 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  GOT [224] {"request":"teardown"}
>     04/09 15:28:50 Trace: [RAAT::SMSL M6] [alsa] teardown
>     04/09 15:28:50 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [219] {"status":"Teardown"}

Signal path and SMSL screen for 24-bit (Qobuz and Local Files):

image

RAAT Server Log for 24-bit:

> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  GOT [213] {"request":"setup","format":{"sample_type":"pcm","sample_rate":96000,"bits_per_sample":24,"channels":2,"sample_subtype":"none"}}
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] alsa output setup: format is pcm 96000/24/2
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] opening [hw:CARD=M6,DEV=0] 96000/24/2
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] prefer larger samples = 0
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [ALSA] [hw:CARD=M6,DEV=0] using hw pcmformat S32_LE bitspersample 24
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [ALSA] [hw:CARD=M6,DEV=0] Requesting 2 periods
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [ALSA] [hw:CARD=M6,DEV=0] Requesting 3840 frames/buffer (1920 frames/period)
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [ALSA] [hw:CARD=M6,DEV=0] Initialized with 2 periods with 1920 frames/period and 3840 frames/buffer
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] sched_setscheduler succeeded
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] samples per buf 1920 ns per buf 20000000 samplerate 96000
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] 1920 samples per buf, 11520 bytes per buf, 15360 bytes per hwbuf
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  got output message {"signal_path": [{"alsa_device": {"longname": "SMSL SMSL M6 at usb-0000:01:00.0-1.4, high speed", "id": "M6", "name": "SMSL M6", "usbid": "0d8c:0004", "mixername": "USB Mixer", "dri
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [output/alsa] [hw:CARD=M6,DEV=0] waiting for device to be ready
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [output/alsa] [hw:CARD=M6,DEV=0] device is ready
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [213] {"message":{"signal_path":[{"type":"output","quality":"lossless","method":"alsa","alsa_device":{"longname":"SMSL SMSL M6 at usb-0000:01:00.0-1.4, high speed","id":"M6","usbid":"0d8c:0004","
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [213] {"audio_port_tcp":44573,"audio_port":0,"clock_port":57178,"status":"Success"}
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  GOT [214] {"request":"stream","stream_id":1043304441,"first_seq":-1,"nak_port":-1,"buffer_size":10,"ready_threshold":0.2}
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [214] {"status":"Buffering"}
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [214] {"status":"Ready"}
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  GOT [215] {"request":"start","min_offset":60875000,"stream_sample":0}
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  Doing ASAP start based on current device clock (min_offset=60875000)
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [214] {"status":"Playing"}
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [215] {"time":22453008533500,"status":"Success"}
> 04/09 15:28:14 Trace: [RAAT::SMSL M6] starting playback: now (22453003062500ns) + ns_per_buf(20000000ns) = 22453023062500ns > 22453008533500ns streamsample=0
> 04/09 15:28:21 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  GOT [216] {"request":"stop"}
> 04/09 15:28:21 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [214] {"status":"Stopped"}
> 04/09 15:28:21 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [216] {"status":"Success"}
> 04/09 15:28:26 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  GOT [217] {"request":"end_stream"}
> 04/09 15:28:26 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [214] {"status":"Ended"}
> 04/09 15:28:26 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [217] {"status":"Success"}
> 04/09 15:28:26 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  GOT [218] {"request":"teardown"}
> 04/09 15:28:26 Trace: [RAAT::SMSL M6] [alsa] teardown
> 04/09 15:28:26 Trace: [RAAT::SMSL M6] [lua@0xb19245c4] [192.168.1.40:58804]  SENT [213] {"status":"Teardown"}

Hello @Ian_Pilborough,

ALSA prefers using S32_LE transport with “zero-padding” when playing 24-bit content to UAC2 devices.

Zero-padding works by adding eight "0"s to the least significant bits of a 24-bit signal.

Any modern device will recognize a 32-bit zero-padded stream, remove the empty bits, and then process it as it were the original 24-bit signal.

-John

3 Likes

Thanks @john that makes sense and is something I’ve heard about, but didn’t know about. I’m happy to continue now.

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