[ubuntu-studio-devel] Audio

Ralf Mardorf ralf.mardorf at alice-dsl.net
Sun Jan 15 21:17:01 UTC 2017

On Sun, 15 Jan 2017 21:59:01 +0300, autumna wrote:
>Alright I'll change the text to being only the sample rate.  

This is what I recommend to do, because nothing else, but jack#s
default 32-bit float matters.

>I was wondering about that 192k, but turns out it was a
>miscommunication. 48k default then. (Just to clarify by the way, the
>values in the mockup are by no means final, or even necessarily
>realistic, my only goal in putting them there is to have a sense of how
>much space and what type of interaction is needed. Thus, while these
>informations on defaults etc help a lot, don't worry that some of them
>might not be accurate. Corrections are appreciated through)  

In regards to space 192000 Hz seems to be the maximum provided by audio
interfaces at the moment.
>> It's not my wording, I quoted Audiobus settings. 128 frames isn't the
>> frame size providing the lowest latency, just Audiobus mentions
>> this. I wouldn't add a recommendation, but the information about
>> device load and response/latency/delay is useful, even a default of
>> 256 is useful for a lot of audio tasks, smaller would be better, but
>> with a max of 256 it becomes interesting for e.g. guitar effects and
>> smaller than 256 easily could cause xruns. For anything else 1024
>> might be the better default. 1024 is the default provided by
>> Jack.    
>Ok, I am not entirely certain I understand this one to revise the
>* Am I understanding you correctly that frame/cycle doesn't affect the
>latency? In that case we just need to correct the text. Just me know
>what it needs to say  

No, you misunderstand my words, frames affect the latency. Audio
interfaces could work at less than 128 frames, at e.g. 64 frames.
<= 256 frames, IOW <= 10 ms are required to use the computer as
guitar effect processor. Stand alone gear should provide a latency of
around <= 5 ms, but actually at around 10 ms they could already be
usable. values much > 10 ms are more or less unusable for this task. ...

>*  We should steer the users toward 2 values, 256 and 1024. Rather than
>256 default, with 128 and 512 there as other solutions. Do I understand
>that correctly?  

... Yes. The default value provided by jack is 1024 frames, > 40 ms.
This ensures that quasi all audio devices will work without xruns, as
long as there are no serious issues, such as fishy hardware and
unfavourable shared IRQs. Even if the audio devices shouldn't provide
zero latency hardware monitoring, a user might have an analog mixing
console or doesn't need to monitor at all. Not all kinds of audio
production require low latency, even not music production.

A user most likely will use the lowest frame value, IOW the lowest
latency. Actually there's no value we really could recommend, because
this depends much on the used hardware.

The jack defaults provided by the jack manpage are more or less safe
values. In short, jack's default is 1024 frames, but for many tasks a
max of 256 frames is required.

Now another issue. If you take a look at QjackCtl you'll see the
rounded calculated values for the in + out latency at a given frames
value, but related to the used hardware and software, the latency could
be higher than the mathematical value. It doesn't matter that much, you
could mention both, frames as well as the round trip latency.

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