Re: [LAU] Jack - buffers V periods

On Wed, 17 Jan 2018 20:21:55 -0500
Tim <termtech@rogers.com> wrote:

>On 01/17/2018 08:04 PM, Paul Davis wrote:
>>
>>
>> On Wed, Jan 17, 2018 at 7:37 PM, Tim <termtech@rogers.com
>> <mailto:termtech@rogers.com>> wrote:
>>
>>
>>
>> On 01/17/2018 06:58 PM, Will Godfrey wrote:
>>
>> I'm getting a little confused when comparing our (Jack) buffer
>> sizes with those
>> discussed on Windows, Mac and general music groups.
>>
>> These latter never mention periods at all, and it's always
>> frames per buffer,
>> so when trying to make comparisons should I take buffers as 1:1
>> or should I be
>> comparing their buffers to our periods?
>>
>>
>> Hi Will.
>>
>> From memory on Windows years ago, and if I understand Jack correctly,
>>  Jack, or more specifically ALSA (in this case let's say using the
>>  ALSA driver), puts you much lower-level towards the sound hardware.
>>
>>
>> ​while true, this is not necessarily a benefit.
>>
>> the better design here is to completely decouple everything as much as
>> possible from device interruptsm and use DLL's to provide sub-sample
>> accurate "prediction" of where an application can read and write at any
>> time.
>
>Ha! Yeah I remember experimenting with that sort of thing.
>Like you're in a race with the DMA pointers. Nice we could read them.
>
>> this allows you to have multiple applications using different buffer
>> sizes (different latency), and to get better latency than the device's
>> inherent interrupt intervals would allow.
>
>I've mused a few times about whether it would be possible to do
> this with Jack midi when using large Jack buffer sizes ;-)
>It's ironic because MusE supports both Jack midi (at say 2048 buffer)
> and ALSA midi (with say 1024 Hz timer) at the same time.
>
>> it's what coreaudio does, and ALSA should do it too. i doubt if it ever
>> will. pulse sort of does this, but all in user space.​
>
>How might sample rate conversion fit into this? Does it make it easier?
>Or no difference, they might slap it on ahead of or after this layer?
>So that say, we might not need the ALSA mixing layer (I forget what
> it's called, dmix?).
>
>T.

Very interesting info here, but I'm trying to understand a scenario where you'd
want different latencies within a single environment.

-- 
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
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