Re: fIsMixable
Re: fIsMixable
- Subject: Re: fIsMixable
- From: BlazeAudio Developer <email@hidden>
- Date: Tue, 17 Jun 2003 18:19:19 -0700
Kurt,
Actually, it is possible to do that with CoreAudio today (we have it
running in one of our drivers).
This requires creating multiple streams on a single AudioEngine (pretty
much like the ASIO channels).
However, if the hardware requires you to send data for all the (20 or
so!) channels to be present in the DMA buffer, the driver has the task of
putting the data in appropriate "slots" - but that also applies for ASIO!
Please note that we ran across some applications' older versions which
did not work well with this scheme (multiple output streams on a single
AudioEngine) - but most newer applications work properly with this
approach.
Thanks.
Devendra.
At 05:47 PM 6/17/2003, Kurt Bigler wrote:
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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