Re: fIsMixable
Re: fIsMixable
- Subject: Re: fIsMixable
- From: Kurt Bigler <email@hidden>
- Date: Tue, 17 Jun 2003 17:47:46 -0700
on 6/17/03 3:22 PM, Jeff Moore <email@hidden> wrote:
>
The latencies for CoreAudio/IOAudio are pretty much the same or better
>
than ASIO for the same piece of hardware. That said, the quality of the
>
driver is just as important, if not more important, on Mac OS X as it
>
is on ASIO for determining the latency.
I have heard that CoreAudio has not yet implemented some stream properties
that would allow a host app to specify in some fashion what channels (or
groups of channels) it really needs to use, so that the driver is not forced
to transfer data for possibly dozens of channels that are not being used at
all by the host app. This I believe corresponds to channel enabling
functionality which in ASIO is implemented on a driver-by-driver basis, so
that a driver who wants there product to perform efficiently in this regard
is able to achieve this.
My understanding is that similar functionality with CoreAudio is not yet
possible, so that manufacturers can in many cases expect worse performance
than was possible under ASIO, when host apps are not using all the channels
that a device offers (or set of devices from the same manufacturer that are
linked together to function as a unit).
This is not a big deal for a stereo device, but any driver that may support
connection of multiple devices often with 20 or so channels per device may
have some significant performance issues when certain groups of channels
(e.g. eight ADAT channels) remain unused on each device.
-Kurt Bigler
>
>
On Tuesday, June 17, 2003, at 2:42 PM, BlazeAudio Developer wrote:
>
>
> Everybody, thank you for your input!!
>
>
>
> I think I will stay away from the Hog mode.
>
>
>
> However, I have related questions (perhaps I should start another
>
> thread).
>
>
>
> How does CoreAudio compare against ASIO (OS9) in terms of workable
>
> latencies, say on a 500 MHz Dual G4, given everything else sort of
>
> equal!
>
>
>
> Thanks.
>
> Devendra.
>
>
>
> At 02:08 PM 6/17/2003, Markus Fritze wrote:
>
>
>
> On Dienstag, Juni 17, 2003, at 01:12 Uhr, James Chandler Jr wrote:
>
>
>
> If just playing or recording a file, it might be desirable to
>
> avoid float-int conversions.
>
>
>
> But in this case performance is not an issue anyhow :-)
>
>
>
> Logic does all it's internal processing in float (or even double, if
>
> necessary). I would expect that every even half-professional audio
>
> application does so, too. You don't have to deal with clipping and
>
> you can do real math without converting (converting float->int is
>
> extremely costly on a PowerPC!). How much effort is even a volume
>
> control with clipping in integer math? It is one cycle in float...
>
>
>
> BTW: On of CoreAudios real advantages _IS_ multi-client support and
>
> the customers love it. Only because they _had_ to use ASIO under Mac
>
> OS 9, doesn't mean that they prefer the old solution.
>
>
>
> Ok, users don't like system beeps on their audio hardware, but they
>
> can change that in the system preferences, so this is no longer a
>
> problem.
>
>
>
> I really would recommend not to deal with hog mode (BTW: we never
>
> tested Logic with hog mode, because AFAIK no audio hardware supports
>
> it :-), your tech support will be flooded (why is iTunes not working,
>
> etc.)
>
>
>
> MMM
>
>
>
> --
>
> Markus Fritze
>
> Apple Computer, Inc. <http://www.apple.com>
>
> Senior Engineer - Audio/Music Applications
>
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