r.pinkston

I have been trying to figure out how to record something into MSP that

is precisely in sync with something being played back by MSP. Any DAW

can do this, of course, but I have not been able to solve the problem

in MSP. I realize that by the time you hear something being played by

MSP, it is already delayed by iovec samples. If you then try to record

something in sync with what you hear, whatever you play will be

delayed by another iovec samples before it gets recorded by MSP.

Presumably then, you need to compensate by 2 * iovec samples, or

possibly by 2 * iovec + sigvec samples, but it still doesn't seem to

be sufficient. I have attached a simple slapback delay patch to

demonstrate my approach. If I add a little feedback to the delay line,

so that a single input will be repeated multiple times at the tap

interval, and then try to play along with the echoes, my new inputs

are invariably behind. If I use a very small iovec, the problem is

less noticeable, but it's still there. Suggestions?

One question that occurred to me was whether I needed to take the

number of channels in my audio hardware into account. I.e., does a

single iovec contain interleaved samples? E.g., if the iovec is 1024

and you have a stereo output device, are there 512 samples for each

I have been trying to figure out how to record something into MSP that
is precisely in sync with something being played back by MSP. Any DAW
can do this, of course, but I have not been able to solve the problem
in MSP. I realize that by the time you hear something being played by
MSP, it is already delayed by iovec samples. If you then try to record
something in sync with what you hear, whatever you play will be
delayed by another iovec samples before it gets recorded by MSP.
Presumably then, you need to compensate by 2 * iovec samples, or
possibly by 2 * iovec + sigvec samples, but it still doesn't seem to
be sufficient. I have attached a simple slapback delay patch to
demonstrate my approach. If I add a little feedback to the delay line,
so that a single input will be repeated multiple times at the tap
interval, and then try to play along with the echoes, my new inputs
are invariably behind. If I use a very small iovec, the problem is
less noticeable, but it's still there. Suggestions?

One question that occurred to me was whether I needed to take the
number of channels in my audio hardware into account. I.e., does a
single iovec contain interleaved samples? E.g., if the iovec is 1024
and you have a stereo output device, are there 512 samples for each
channel contained in a single iovec?

latency

no its per channel. but the hardware&driver itself also has a delay which will add up.

should be something around 4-20 ms depending on your IO.

try to sync it by hand by using a click (exact spikes please) track then you will see if everything is ok.

once measured the delay should stay true until tomorrow.

no its per channel. but the hardware&driver itself also has a delay which will add up. 

try to sync it by hand by using a click (exact spikes please) track then you will see if everything is ok.
once measured the delay should stay true until tomorrow.

Latency