M-Audio C600 - SPDIF weirdness

[email protected] Tue, 26 May 2026 22:13:33 -0400

Newsgroups	org.alsa-project.alsa-devel
Message-ID	<[email protected]>

Hi all,
In attempting to validate a 'live mixer' application for the C600, I 
noticed some weirdness I can't explain. This weirdness may indicate an 
issue with the driver.

1). Device is a 8-ch output, ch 1-6 are analogue outputs (balanced TRS) 
and ch7/8 are sent out of the SPDIF port.

'aplay -L' shows a SPDIF output, but this does NOT accept 2 channel out 
and DOES accept 8 channel output
---
$ aplay sin1k.wav -D "iec958:CARD=C600,DEV=0"
Playing WAVE 'sin1k.wav' : Signed 24 bit Little Endian in 3bytes, Rate 
48000 Hz, Stereo
aplay: set_params:1377: Channels count non available
---
$ aplay sin1k.wav -D "iec958:CARD=C600,DEV=0"
Playing WAVE 'sin1k.wav' : Signed 24 bit Little Endian in 3bytes, Rate 
48000 Hz, Channels 8
^CAborted by signal Interrupt...
--
With 8-ch output, the analogue (TRS) outputs the audio as well as the 
SPDIF output.


2). When a 'loop back' cable is used (from SPDIF out -> SPDIF in), you 
must (repeatably) select 'clock source' as 'SPDIF' and then something 
can be heard - but it is NOT the proper audio, it's a few clicks which 
suggests C600 can not sync/decode it's own output.

If the 'clock source' is internal, there is no audio captured.


3). If the C600's SPDIF output is connected to a 2nd device (Digi002R) 
then the audio DOES decode properly, and if I make connections (in Jack) 
to loop Digi's SPDIF IN -> Digi's SPDIF Out the received SPDIF at the 
C600 sounds correct too...

The Digi002R is running at 48KHz (same a C600), but I don't know what 
bit-depth. I don't see any place to change this within qJackCtrl.


Any suggestions as to what might be going on with the loop-back 
'clicking audio'?
Simon

arecord_C600_devices.txt (text/plain, 510 B)

hw:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    Direct hardware device without any conversions
plughw:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    Hardware device with all software conversions
sysdefault:CARD=C600
    Fast Track C600, USB Audio
    Default Audio Device
front:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    Front output / input
dsnoop:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    Direct sample snooping device
usbstream:CARD=C600
    Fast Track C600
    USB Stream Output

aplay_C600_devices.txt (text/plain, 1.3 KB)

hw:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    Direct hardware device without any conversions
plughw:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    Hardware device with all software conversions
sysdefault:CARD=C600
    Fast Track C600, USB Audio
    Default Audio Device
front:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    Front output / input
surround21:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    2.1 Surround output to Front and Subwoofer speakers
surround40:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    4.0 Surround output to Front and Rear speakers
surround41:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
iec958:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    IEC958 (S/PDIF) Digital Audio Output
dmix:CARD=C600,DEV=0
    Fast Track C600, USB Audio
    Direct sample mixing device
usbstream:CARD=C600
    Fast Track C600
    USB Stream Output