ALSA and RME Raydat troubleshooting

Vaclav Mach <vaclav.mach@xxxxxxxxxxxx> · Tue, 21 Oct 2014 13:20:38 +0200

Hi all,

I'm the team leader of Voice Communication Systems development in ARTISYS company. We try to utilize RME RayDat sound device on Linux system with ALSA sound interface. After a lot of experiments we are not able to set up proper sound output from this device, so we kindly ask you for a help to solve our problem. Here is a brief description:

General task of our troubleshooting is that our audio signal output is not continuous. The output signal is rather interrupted. Here is our configuration:

PC with Linux (kernel v. 3.17.0) with ALSA sound libraries compiled in kernel. We have also additional packages installed: alsa-tools, alsa-utils and alsa-lib (all version 1.0.28).

Inside the PC there is PCI Express card RME Raydat, whose drivers are also compiled in the Linux kernel. This interface is connected by optical fibres (ADAT) to the Ferrofish A16 MK-II (2 pairs of TOSLINK cables).

Playing test files using commands

aplay -D pcm.out_test -r 48000 -f S32_LE /usr/share/sounds/alsa/Front_Left.wav -vv 
and
aplay -D pcm.out_test2 -r 48000 -f S32_LE /usr/share/sounds/alsa/Front_Right.wav -vv

causes audible interruptions. The configuration of the ALSA device is following:

pcm.out_dmix {
	type dmix
	ipc_key 56874
	ipc_key_add_uid false
	ipc_perm 0666
	slave {
		pcm "hw:2,0"
		period_size 2048
		channels 36
		rate 48000
	}
	bindings {
		0 0 # from 0 => to 0
		1 1 # from 1 => to 1
	}
}

pcm.out_test {
	type plug
	slave.pcm "out_dmix"
	ttable.0.0 1
}

pcm.out_test2 {
	type route
	slave.pcm "out_dmix"
	ttable.0.1 1
}

Let me describe other two example experiments:

1. If I try to record sound using the same parameters as out_dmix device but of type "dsnoop" (equivalent of dmix for capturing), there are no interruptions and the recorded sound is perfect.

2. If I play single sound file to the output of the RME card while the ALSA device is of type "route", the sound output is perfect. Playing second file on different output channel this way I'm not able to open
other output channel simultaneously by another program because the device is busy. There is this experiment's ALSA device configuration:

pcm.out_test {
	type route
	slave.pcm "hw:2,0"
	slave.format "S32_LE"
	slave.channels 36
	ttable.0.0 1
}
pcm.out_test2 {
	type route
	slave.pcm "hw:2,0"
	slave.format "S32_LE"
	slave.channels 36
	ttable.0.1 1
}
This should be solved by "dmix" type ALSA device, which currently causes interruptions in our configuration.

The question is: how can we play multiple audio streams to multiple output channels using our equipment?

Thank you. 
Dear Mr. Knoth,