[Ardour-Users] jackd --sync

Giso Grimm gg3137 at vegri.net
Mon Aug 19 23:33:08 PDT 2019

On 19.08.19 09:54, Will Godfrey wrote:
> On Mon, 19 Aug 2019 08:41:44 +0200
> Giso Grimm <gg3137 at vegri.net> wrote:
>> On 18.08.19 22:11, jonetsu wrote:
>>> Hello,
>>> From time immemorial I always copy/pasted the same jackd command line.
>>> And basically never questioned much about the other params except the
>>> three last one which I've adjusted.
>>> /usr/bin/jackd --sync -P80 -ndefault -dalsa -dhw:M1010LT -r44100 -p512
>>> -n8
>>> This is about:
>>> jackd   5   
>>> jackd2  1.9.12~dfsg-2
>>> My question is, what is the purpose of the --sync option ?  
>> with --sync, jack2 behaves the same way as jack1 in the way of
>> scheduling the clients (no parallel graphs, but one block less
>> processing delay).
>> The --sync is important when extreme low delay processing matters -
>> without the flag, jack2 uses three buffers even when set to two.
>> This was recently discussed on the jack-dev list ("What about the number
>> of buffers?").
> Interesting. I never knew that.
> As an aside, does anyone know what qjackctl does about this?
> I always start jack with that at switch-on regardless of what other
> audio software I use.

as far as I know qjackctl has no graphical equivalent to this option. In
my setup I added this option to the server prefix field (in Advanced
tab), i.e. server prefix is

"/usr/bin/jackd --sync"

Probably the best documentation of jack2 --sync/jack1 behavior can be
found in Robins answer here:


Maybe this should find its way into the man pages...

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