[LAU] kernel 5.15 irqs

[Len Ovens]

On Fri, 25 Feb 2022, Jeremy Jongepier wrote:

> On 24-02-2022 19:57, Len Ovens wrote:
>> While there have been many rules of thumb in the past for tuning a system 
>> for audio, the reality is that each system is different and requires 
>> different steps (with testing).
>
> Those rules of thumb should still apply mostly.

The word "mostly" pretty much sums it up. There is no low latency audio 
recipe that can be dropped in and just work. Each machine/device 
combination will require tweaking. For some of us that tweaking comes 
naturally (I generally don't really notice what I do to achieve a good 
result) but when I try explaining it to someone else via email or irc, it 
is obvious that many people either do not find it very natural or just 
have an unsuitable machine.

> The other reality is that some
>> of the newer systems have fewer choices (like laptops) and the user will 
>> just have to get used to higher latency audio use.
>
> Personally I think every system is tunable/tweakable to a certain degree. 
> Haven't come across a system yet that I couldn't get to run low latency audio 
> within the limits of that system and I've tried quite a few.

"to a certain degree" and "within the limits of that system" seem to me to 
be saying the same thing. each system has a limit as to how well it will 
do low latency audio and the user will have to live within that.

> Of course USB 2.0
>> audio has it's own group of difficulties as well.
>
> Which ones? Can't think of anything else but class compliance.

The same audio device plugged into different physical ports on most 
machines will yield different results, I would say newer mother boards but 
maybe newer kernels because I used to be able to at least raise the 
priority of one port over the next, but at some point it did not make any 
difference which port I plugged into my device ends up on the same USB bus 
as everything else (printer, mouse, keyboard, webcam, external drive, 
etc). The only cure seems to be adding a dedicated PCIe USB card for the 
device. Class compliance is merely the entry fee to get audio in and out 
of the machine. One can record and play back with that and use external 
monitoring no problem. Using a set of drum pads with a soft synth maybe 
not. It seems a firewire device using the ffado driver for jack, out 
performs any USB device.

Just as a reference, I have noticed, in a live situation with all analog 
equipment, that by the time I get 30 feet away from monitors and FOH, my 
timing suffers. Latency matters.

--
Len Ovens
www.ovenwerks.net