Music servers / network players with realtime kernel?

[FredericV]

Linux has several audio / audiophile / DAW distributions with a realtime kernel. But these are most self- or community supported.

Are there any music servers or players with a realtime kernel and/or realtime OS?

[mansr]

Why do you think you need an RTOS for a music server?

[Jud]

16 minutes ago, FredericV said:

Linux has several audio / audiophile / DAW distributions with a realtime kernel. But these are most self- or community supported.

Are there any music servers or players with a realtime kernel and/or realtime OS?

 

Certainly Ubuntu has low-latency kernels, and I believe a real-time or nearly so option as well. I imagine this is so for most of the major Linux distributions and their server versions. 

 

To mansr's question, I'm supposing there may be some advantages to low latency in some respects (Miska offers a customized kernel with some low-latency tweaks), but I also recall reading about some situations where you might actually want some ability to carry out asynchronous operations.  

 

So is it as simple as low latency is good, the lower the better? Or are there specific operations you want done in real time?

[marce]

RTOS's are used for industrial control, as are the industrial busses, they are there because you need to have guaranteed times for things to happen (such as a stop command), PC's etc. are not and do not need to be real time for basic tasks, you press a button and music plays or you get a print out, if it takes 20ms or 200ms no-one cares or worries, if you are controlling a production line or similar things have to happen at known times, so you use a RTOS. I've played with OS9, with G64/96 and VME based products, one we did was comms. for the ADC racks at the Daresbury ring using the Topaz network as an interface and G64 based boards running OS-9, there you need to work in real time, because you have to re-act in real time... Music playback is basically file transfer, and not that arduous, you spit out a few bits and send them via a link to a DAC... simple.

 

[marce]

3 minutes ago, Jud said:

 

 

So is it as simple as low latency is good, the lower the better? Or are there specific operations you want done in real time?

You press play, you get music, usually instantaneously, what more would you want.....?

[mansr]

Strictly speaking, music playback is a real-time task. If the output buffer doesn't get filled in a timely manner, there audio will stutter. The differences from industrial control systems are twofold. Firstly, latency is practically a non-issue. If the output buffer hold several hundred milliseconds, something truly exceptional would have to happen for the system not to keep up even if there are no hard guarantees. Secondly, if the deadline isn't met, the worst that can happen is that your music playback glitches. It doesn't blow up half a town. It is simply not worth the much higher cost to ensure that a buffer underrun never, ever happens. This goes beyond the software and OS too. Standard PC hardware is not suitable for a true real-time system. There are far too many unpredictable things that can happen.

[marce]

Yes I agree there is the streaming issue, but its usually a single computer doing one or two tasks and as you have stated, its not hard...

I have done intensive CAD work and played music and never noticed an issued with stuttering, the only time I have had problems is using a Squeezebox touch wireless through a few stone walls and a cheap ebay Ethernet cable soon solved that issue (about £10 for a 20' cable... obviously non audiophile).

 

[Jud]

35 minutes ago, marce said:

I've played with OS9, with G64/96 and VME based products

 

I liked playing around with QNX - thought the "Photon microGUI" was well done.

[mansr]

The weirdest RTOS I've ever used was probably OSE.

[Jud]

Audirvana+ and XXHighEnd both are "memory players," based on the notion that timing of playback vs. timing of DSP should be controllable.  Whatever one thinks of this idea, it's somewhat contrary to the low latency concept. 

[mansr]

If you're playing, say, Sgt. Pepper, the latency is already 50 years. What's another 100 milliseconds?

[Guest]

The case for a "RT Kernel" as diminished over the years, so even those who used to use it in their personal rigs are happily living without it.

 

The thread prioritization and process affinity etc can still be done and the modern kernels handle processes and threads just fine.