Re: Does anyone get an AudioDevice that has both input and output channels? (question is related to software play through)
Re: Does anyone get an AudioDevice that has both input and output channels? (question is related to software play through)
- Subject: Re: Does anyone get an AudioDevice that has both input and output channels? (question is related to software play through)
- From: "B.J. Buchalter" <email@hidden>
- Date: Thu, 19 Jul 2001 11:02:36 -0400
Hi Jeff,
on 7/18/01 9:06 PM, Jeff Moore at email@hidden wrote:
>
on 7/18/01 3:29 PM, B.J. Buchalter <email@hidden> wrote:
>
>
> If individual devices don't support this, so be it -- they
>
> are not suitable for professional audio work.
>
>
Tell that to the folks working with USB devices. They might take exception
>
to this. As Bill said, the way the USB audio spec works makes this situation
>
come up immediately. I daresay that there will be lots of folks doing pro
>
audio type things using USB devices.
These are pro-sumer devices. Anything that *requires* SRC for full duplex
operation is not professional audio. There are definitely devices on the USB
bus that provide pro-level performance on input. AFAIK USB audio output is
by definition based upon software SRC/PLL. I could be wrong as I have not
checked on the parts recently. This approach is not professional (by the
standards of the professional audio industry). This is not to say that pro's
won't use them, but they won't be used for critical applications. The issue
here is that professional applications have stringent requirements. If the
architecture supports the requirements (as it appears to) it will be used.
It it does not, it will not be used, just as sound manager was not used for
professional applications. Quicktime has evolved from postage stamp cartoons
to professional applications. This evolution took place because the
architecture was flexible enough to support it, and because Apple decided it
was important and listened to the external folks who had professional
requirements. If Quicktime had not evolved to support Pro Applications, no
pro applications would have been built upon it.
The point is that people are asking these questions because they have real
and genuine concerns and have a desire to be able to use CoreAudio for their
applications, instead of having to decend back into the morass that we have
under OS 9.
Hi Laurent,
on 7/19/01 2:01 AM, Laurent Cerveau at email@hidden wrote:
>
As for the built-in hardware : having it presented as two devices or one
>
change nothing.
>
It is just a convenience in term of application developer, and it makes
>
more sense as the
>
2 hardware DMA engines on the mac IO controller are driven by the same
>
clock, and
>
won't drift (so this is a good candidate for presenting synchronized
>
IO). We are plenty
>
aware of that. But that won't make the samples come and go faster (or
>
slower) into
>
the machine, or to/from the HAL :-).
Yes, but.... having a unified IOProc allows you to *know* that the inputs
and outputs are synchronized -- so you do not have to worry about SRC. It
also allows you do minimum latency software foldback/loopback in the IOProc,
without having to build a secondary transfer buffer. If the IOProcs are
split, you have to (1) divine that they are syncronized, or (2) SRC them
just in case. Either way, you need to add an additional buffer between the
two procs, which even at 64 samples, coupled with the (audio) hardware
latencies is starting to cross the edge of perceivability. So, as I said
before -- it is good that the architecture supports the unified model. It
will be good when the built-in audio driver supports the unified model.
Professional products will support the unified model. Having two syncronized
devices are not the same as one unified device. That is not to say that
application can't get around it, but is more than a matter of convienence.
Best regards,
B.J. Buchalter
Metric Halo
M/S 601 - Building 8
Castle Point Campus
Castle Point, NY 12511-0601 USA
tel +1 845 831-8600
fax +1 603 250-2451
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