On Mon, Jan 19, 2004 at 02:56:52AM +0100, Fons Adriaensen wrote:
The point is IMHO that JACK is great for making audio connections between independent Linux processes - that what it's designed for, and what it does extremely well (BTW congrats to Paul and the whole JACK team for the Open Source Award). But using JACK for internal connections is pure overkill, and I'm not even sure it will work as you expect.
Sorry to follow upp on my own ramblings, but I'm getting more and more convinced that using JACK for internal connections in a modular synth will
not work as expected.
For example, take the patch
JACK -> A -> JACK -> B -> JACK
where A and B are two processing modules.
If A and B are inside the same JACK client, what will happen ?
Will jack use a single buffer for A-out and B-in (this is what you'd
expect in a modular synth), or will it copy the previous A-out to B-in
before calling your process callback, thereby introducing one cycle
delay ?
If A and B are modules *inside the same JACK client* (rather than, for instance, two JACK clients instantiated by the same application) then the situation is something like this:
+---------------+
| +-------+ |
JACK ------>|-> A ->|---+
| | |
+-->|-> B ->|----------> JACK
+-------+Note that the client contains connectivity that is invisible to JACK: As far as
JACK can tell the client is a black box with 2 inputs and 2 outputs, requiring
a single process callback (which is all that a client is going to get in any case).
Will a delay be introduced? Not so long as the client processes A before B in its callback. But *neither JACK nor the client* posesses the information to determine that this is the correct order!
Worse:
JACK -> A -> JACK -> C -> JACK -> B -> JACK
Where C is in a separate client.
Now...
+-------+
| | +---|<- C <-|<--+
| | | | | +-------+ |
| |
| +-------+ |
JACK ------>|-> A ->|---+
| | |
+-->|-> B ->|----------> JACK
+-------+
Oh dear... C needs to be called between A and B, but even if JACK and the two clients know that A->C->B is the correct order (which none of them do) it can't be achieved because A and B must be processed in a single callback.
Simon Jenkins (Bristol, UK)
