Re: [Linuxsampler-devel] Re: [Linuxsampler-devel] RAM sampler module proposal

[Benno S. <be...@ga...>]

On Fri, 2002-11-08 at 13:12, Phil Kerr wrote:
> Although this speed is the official spec I've found that ALSA, and a
> number of MIDI cards, do not seem to throttle data back to the spec and
> will pass data though the interface at reception speed.  Although this
> is a wider problem for me regarding DMIDI and hardware it's potentially
> a good thing when we are dealing with software based D/MIDI applications
> (10 Gbit MIDI :).  

yes, of course that's why I prefer the
PC sequencer -> internal MIDI -> PC software synth/sampler
solution over using external gear. Timing will be very tigh and chords
do not suffer from smearing.
In fact in some extreme test cases with my proof-of-concept code where
flooded it with aligned note-on events there were CPU overloads
due to the voice initialization code eating away a few cycles.
Probably we will need to limit the note-on's per fragment in order to 
level out these CPU load peaks, especially when using very small
fragment sizes (32-64 samples) with bigger fragment sizes there is
plenty of time for handling the note events.

> 
> So regarding MIDI timing I get the impression that PC host based
> interfaces cannot guarantee the 31.25k rate, but testing is not
> conclusive.

No that is not true.
Some sound cards do not have MIDI RX or TX interrupts and force the
driver to go into polling mode which means either high CPU usage or low
throughput. (see the soundblaster awe 64 midi out -> no tx irq -> midi
sucks :-) )
With other cards like the Hoontech you get note-on midi-out-to-in
latency that matches the wire speed.
Looong time ago I wrote a tittle tool that does this 
http://www.gardena.net/benno/linux/mididelay-0.1.tgz

Paul Davis and others (using decent midi cards) reported 1.1 msec 
note-on midi-out-to-in latency which matches the wire speed.
On the SB AWE64 I got about 10 msec (due the lack of a TX irq) plus when
 midi out traffic is very heavy the machine slows down to a crawls
(using OSS/Free).

So before buying a MIDI card pay attention that both RX and TX irqs are
present.

But my prefered MIDI "cable" between two boxes will be DMIDI over
100Mbit LAN anyway.  :-)

PS: does sound my RAM sample module reasonable ? (taking into account
the suggestions you guys gave here like Steve's modulation rate
reduction etc).
If there are not objections I'm going to write some code and make the
 sampling module "audible". :-)

cheers,
Benno

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