[LAU] Ardour export question...

Len Ovens len at ovenwerks.net
Thu Mar 19 16:14:30 UTC 2015

On Thu, 19 Mar 2015, Dale Kazakore Powell wrote:

> On 09/03/15 04:58, Fons Adriaensen wrote:
>> On Sun, Mar 08, 2015 at 08:34:42PM +0000, alexus / dotcommon wrote:
>>> (Please excuse if this is a stupid question...)
>>> I am learning Ardour doing some practice on my system (Debian
>>> stable, RT kernel, RT tuning, MAudio Audiophile 2496 PCI, 3GHz 4core
>>> CPU, 8GB RAM, JACK buffer 512). Working with a 3min stereo audio
>>> (24bit, 88.1kHz) I have noticed DSP goes to 100% when exporting
>>> (WAV)...
>>> Is it normal (simply Ardour is using all the available resources
>>> during the export) or something is going wrong (and I will have
>>> glithces/pops in the output file)?
>> It's perfectly normal. Export puts Jack in 'freewheeling' mode
>> which means that it doesn't sync to the soundcard but starts
>> a new cycle as soon as the previous one has ended (the sound
>> card output gets 'silence' for output meanwhile, and input is
>> discarded). So things will run 'as fast as possible' which
>> means CPU load will go up to 100%.
>> Ciao,
> But what if you want to listen to audio from a different application 
> connected to Jack while exporting? Surely it should just disconnect from Jack 
> (although this could possible cause routing issues on reconnecting once 
> finished) and run as fast as possible using max CPU cycles.

When you do this, does the CPU load still go to 100%? Ardour may not be 
able to switch Jack to freewheeling while another application is connected 
to one of the HW ports and so exporting would be done at RT speed. This is 
not a good idea if you are close to the edge with effects/softsynths as 
freewheeling does not ever have xruns. Also, export speed will be improved 
if jack can freewheel even in a case where cpu use is quite high in RT.

Len Ovens

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