Re: [LAU] Large live recrodings ?

Am Mittwoch, 2. Juli 2008 schrieb Kjetil S. Matheussen:
> Arnold Krille:
> > Am Mittwoch, 2. Juli 2008 schrieb Kjetil S. Matheussen:
> > > I think that is complete overkill. I just tried recorded 128 channels
> > > of 32bit/44100hz at once, without problem. And my machine is 5 years
> > > old 2Gz barebone, using only a single PATA ide disk.
> > > This was using jack_capture, and only recording silence (ie.
> > > non-connected jack ports). Maybe the silence makes a difference.(?)
> >
> > For jack and ardour/timemachine/jack_capture it is completely irrelevant
> > if the double-numbers contain 0.0, 1E-<incredibly high> or some
> > (pseudo-)random
> > values between -1 and 1. Its still sizeof(double) that is saved to disk
> > for each channel and sample...
> >
> > It only makes a difference when using compressed formats like mp3, flac,
> > etc. But ardour doesn't support this (yet).
>
> You can't just bombastically spew out things like that without
> backing it up with some sort of facts or at least arguments.
> Since the buffers isn't written to by anything other than zeros,
> there could theoretically be a smaller chance of cache misses. Whether it
> makes a difference is a different story.

As the transfer from memory to hd is _the_ slow point of the setup,
cache-misses or hits don't influence that at all. And when you are not
calculating anything (apart from 64bit to 32bit double-to-float), you don't
access the cache. DMA is the keyword. Still it doesn't make saving to disk
faster than your disks and controllers speed. And I am pretty sure that there
is _no_ compression involved in that part, otherwise this would seriously
affect data-integrity if the controller did an unwanted compression.

Is that enough back-up for my "bombastically spilled out" argumentation?
A double (or float) to transfer to disk is still a double (float) to transfer
to disk regardless wether the value is 0, close to zero or something close to
INFINITY...

Arnold

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